automobile technology
TRANSCRIPT
A chassis consists of an internal framework that supports a man-made object. It is
analogous to an animal'sskeleton. An example of a chassis is the underpart of a motor
vehicle, consisting of the frame (on which the body is mounted) with the wheels and
machinery.
Examples of use
Vehicles
1950s Jeep FC cowl and chassis for others to convert into finished vehicles
In the case of vehicles, the term chassis means the frame plus the "running gear"
like engine, transmission, driveshaft, differential, and suspension. A body (sometimes
referred to as "coachwork"), which is usually not necessary for integrity of the structure, is
built on the chassis to complete the vehicle. Forcommercial vehicles chassis consists of an
assembly of all the essential parts of a truck (without the body) to be ready for operation on
the road.[1] The design of a pleasure car chassis will be different than one for commercial
vehicles because of the heavier loads and constant work use.[2] Commercial vehicle
manufacturers sell “chassis only”, “cowl and chassis”, as well as "chassis cab" versions that
can be outfitted with specialized bodies. These include motor homes, fire
engines, ambulances, box trucks, etc.
In particular applications, such as school busses, a government agency like National
Highway Traffic Safety Administration (NHTSA) in the U.S. defines the design standards of
chassis and body conversions.[3]
An armoured fighting vehicle's chassis comprises the bottom part of the AFV that includes
the tracks, engine, driver's seat, and crew compartment. This describes the lower hull,
although common usage of might include the upper hull to mean the AFV without the turret. A
chassis serves as basis for platforms on tanks, armored personnel carriers,combat
engineering vehicles, etc.
Frame (vehicle)
From Wikipedia, the free encyclopedia
Cross section of a Chevy Silverado HD 2011 frame
A frame is the main structure of the chassis of a motor vehicle. All other components fasten
to it; a term for this is design is body-on-frameconstruction.
In 1920, every motor vehicle other than a few cars based on motorcycles had a frame. Since
then, nearly all cars have shifted to unit-body construction, while nearly all trucks and buses
still use frames.
Construction
There are three main designs for frame rails. Their cross-sections include:
1. C-shaped
2. Boxed
3. Hat
[edit]C-shape
By far the most common, the C-rail has been used on nearly every type of vehicle at one time
or another. It is made by taking a flat piece of steel (usually ranging in thickness from 1/8" to
3/16") and rolling both sides over to form a c-shaped beam running the length of the vehicle.
[edit]Boxed
Originally, boxed frames were made by welding two matching c-rails together to form a
rectangular tube. Modern techniques, however, use a process similar to making c-rails in that
a piece of steel is bent into four sides and then welded where both ends meet.
In the 1960s, the boxed frames of conventional American cars were spot-welded here and
there down the seam; when turned into NASCAR "stock car" racers, the box was
continuously welded from end to end for extra strength (as was that of the Land-Rover from
its first series).
1956 Chevrolet 1/2-ton frame. Notice hat-shaped crossmember in the background, c-shape
rails and crossmember in center, and a slight arch over the axle.
.
[edit]Hat
Hat frames resemble a "U" and may be either right-side-up or inverted with the open area
facing down. Not commonly used due to weakness and a propensity to rust, however they
can be found on 1936-1954 Chevrolet cars and some Studebakers.
Abandoned for a while, the hat frame gained popularity again when companies started
welding it to the bottom of unibody cars, in effect creating a boxed frame.
[edit]Design Features
While appearing at first glance as a simple hunk of metal, frames encounter great amounts of
stress and are built accordingly. The first issue addressed isbeam height, or the height of the
vertical side of a frame. The taller the frame, the better it is able to resist vertical flex when
force is applied to the top of the frame. This is the reason semi-trucks have taller frame rails
than other vehicles instead of just being thicker.
Another factor considered when engineering a frame is torsional resistance, or the ability to
resist twisting. This, and diamonding (one rail moving backwards or forwards in relation to the
other rail), are countered by crossmembers. While hat-shaped crossmembers are the norm,
these forces are best countered with "K" or "X"-shaped crossmembers.
As looks, ride quality, and handling became more of an issue with consumers, new shapes
were incorporated into frames. The most obvious of these are arches and kick-ups. Instead
of running straight over both axles, arched frames sit roughly level with their axles and curve
up over the axles and then back down on the other side for bumper placement. Kick-ups do
the same thing, but don't curve down on the other side, and are more common on front ends.
On perimeter frames, the areas where the rails connect from front to center and center to
rear are weak compared to regular frames, so that section is boxed in, creating what's known
as torque boxes.
Another feature seen are tapered rails that narrow vertically and/or horizontally in front of a
vehicle's cabin. This is done mainly on trucks to save weight and slightly increase room for
the engine since the front of the vehicle doesn't bear as much of a load as the back.
2007 Toyota Tundra chassis showing an x-shaped crossmember at the back.
The latest design element is frames that use more than one shape in the same frame rail. For
example, the new Toyota Tundra uses a boxed frame in front of the cab, shorter, narrower
rails underneath the cab for ride quality, and regular c-rails under the bed.
[edit]Types
[edit]Ladder Frame
So named for its resemblance to a ladder, the ladder frame is the simplest and oldest of all
designs. It consists merely of two symmetrical rails, or beams, and crossmembers connecting
them. Originally seen on almost all vehicles, the ladder frame was gradually phased out on
cars around the 1940s in favor of perimeter frames and is now seen mainly on trucks.
This design offers good beam resistance because of its continuous rails from front to rear,
but poor resistance to torsion or warping if simple, perpendicular crossmembers are used.
Also, the vehicle's overall height will be higher due to the floor pan sitting above the frame
instead of inside it.
[edit]Backbone tube
Main article: Backbone chassis
Backbone chassis is a type of an automobile construction chassis that is similar to the body-
on-frame design. Instead of a two-dimensional ladder type structure, it consists of a strong
tubular backbone (usually rectangular in cross section) that connects the front and rear
suspension attachment areas. A body is then placed on this structure.
[edit]Perimeter Frame
Similar to a ladder frame, but the middle sections of the frame rails sit outboard of the front
and rear rails just behind the rocker panels/sill panels. This was done to allow for a lower
floor pan, and therefore lower overall vehicle in passenger cars. This was the prevalent
design for cars in the United States, but not in the rest of the world, until the uni-body gained
popularity and is still used on US full frame cars. It allowed for annual model changes
introduced in the 1950s to increase sales, but without costly structural changes.
In addition to a lowered roof, the perimeter frame allows for more comfortable lower seating
positions and offers better safety in the event of a side impact. However, the reason this
design isn't used on all vehicles is that it lacks stiffness, because the transition areas from
front to center and center to rear reduce beam and torsional resistance, hence the use of
torque boxes, and soft suspension settings.
[edit]Superleggera
An Italian term (meaning "super-light") for sports-car construction using a three-dimensional
frame that consists of a cage of narrow tubes that, besides being under the body, run up the
fenders and over the radiator, cowl, and roof, and under the rear window; it resembles a
geodesic structure. The body, which is not stress-bearing, is attached to the outside of the
frame and is often made of aluminium.
[edit]Unibody
Main article: Unibody
By far the most common design in use today, sometimes referred to as a sort of frame.
But the distinction still serves a purpose: if a unibody is damaged in an accident, getting bent
or warped, in effect its frame is too, and the vehicle undrivable. If the body of a body-on-
frame vehicle is similarly damaged, it might be torn in places from the frame, which may still
be straight, in which case the vehicle is simpler and cheaper to repair.
[edit]Sub Frame
Main article: Subframe
The sub frame, or stub frame, is a boxed frame section that attaches to a unibody. Seen
primarily on the front end of cars, it's also sometimes used in the rear. Both the front and rear
are used to attach the suspension to the vehicle and either may contain
the engine and transmission
Basic Engine Parts
The core of the engine is the cylinder, with the piston moving up and down inside the
cylinder. The engine described above has one cylinder. That is typical of most lawn mowers,
but mostcars have more than one cylinder (four, six and eight cylinders are common). In a
multi-cylinder engine, the cylinders usually are arranged in one of three
ways: inline, V or flat (also known as horizontally opposed or boxer), as shown in the
following figures.
Different configurations have different advantages and disadvantages in terms of
smoothness, manufacturing cost and shape characteristics. These advantages and
disadvantages make them more suitable for certain vehicles.
Figure 3. V - The cylinders are arranged in two banks set at an angle to one another.
Figure 4. Flat - The cylinders are arranged in two banks on opposite sides of the engine.
Let's look at some key engine parts in more detail.
Spark plug
The spark plug supplies the spark that ignites the air/fuel mixture so that combustion can
occur. The spark must happen at just the right moment for things to work properly.
Valves
The intake and exhaust valves open at the proper time to let in air and fuel and to let out
exhaust. Note that both valves are closed during compression and combustion so that the
combustion chamber is sealed.
Piston
A piston is a cylindrical piece of metal that moves up and down inside the cylinder.
Piston rings
Piston rings provide a sliding seal between the outer edge of the piston and the inner edge of
the cylinder. The rings serve two purposes:
They prevent the fuel/air mixture and exhaust in the combustion chamber from leaking
into the sump during compression and combustion.
They keep oil in the sump from leaking into the combustion area, where it would be
burned and lost.
Most cars that "burn oil" and have to have a quart added every 1,000 miles are burning it
because the engine is old and the rings no longer seal things properly.
Connecting rod
The connecting rod connects the piston to the crankshaft. It can rotate at both ends so that its
angle can change as the piston moves and the crankshaft rotates.
Crankshaft
The crankshaft turns the piston's up and down motion into circular motion just like a crank on
a jack-in-the-box does.
Sump
The sump surrounds the crankshaft. It contains some amount of oil, which collects in the
bottom of the sump (the oil pan).
Internal combustion engine cooling
From Wikipedia, the free encyclopedia
Internal combustion engine cooling refers to the cooling of an internal combustion engine,
typically using either air or a liquid.
[edit]Overview
Heat engines generate mechanical power by extracting energy from heat flows, much as
a water wheel extracts mechanical power from a flow of mass falling through a distance.
Engines are inefficient, so more heat energy enters the engine than comes out as
mechanical power; the difference is waste heat which must be removed. Internal combustion
engines remove waste heat through cool intake air, hot exhaust gases, and explicit engine
cooling.
Engines with higher efficiency have more energy leave as mechanical motion and less as
waste heat. Some waste heat is essential: it guides heat through the engine, much as a
water wheel works only if there is some exit velocity (energy) in the waste water to carry it
away and make room for more water. Thus, all heat engines need cooling to operate.
Cooling is also needed because high temperatures damage engine materials and lubricants.
Internal-combustion engines burn fuel hotter than the melting temperature of engine
materials, and hot enough to set fire to lubricants. Engine cooling removes energy fast
enough to keep temperatures low so the engine can survive.
Some high-efficiency engines run without explicit cooling and with only accidental heat loss, a
design called adiabatic. For example, 10,000 mile-per-gallon "cars" for the Shell economy
challenge[1] are insulated, both to transfer as much energy as possible from hot gases to
mechanical motion, and to reduce reheat losses when restarting. Such engines can achieve
high efficiency but compromise power output, duty cycle, engine weight, durability, and
emissions.
[edit]Basic principles
Most internal combustion engines are fluid cooled using either air (a gaseous fluid) or a liquid
coolant run through a heat exchanger (radiator) cooled by air. Marine engines and some
stationary engines have ready access to a large volume of water at a suitable temperature.
The water may be used directly to cool the engine, but often has sediment, which can clog
coolant passages, or chemicals, such as salt, that can chemically damage the engine. Thus,
engine coolant may be run through a heat exchanger that is cooled by the body of water.
Most liquid-cooled engines use a mixture of water and chemicals such as antifreeze and rust
inhibitors. The industry term for the antifreeze mixture is engine coolant. Some antifreezes
use no water at all, instead using a liquid with different properties, such as propylene
glycol or a combination of propylene glycol and ethylene glycol. Most "air-cooled" engines
use some liquid oil cooling, to maintain acceptable temperatures for both critical engine parts
and the oil itself. Most "liquid-cooled" engines use some air cooling, with the intake stroke of
air cooling the combustion chamber. An exception isWankel engines, where some parts of
the combustion chamber are never cooled by intake, requiring extra effort for successful
operation.
There are many demands on a cooling system. One key requirement is that an engine fails if
just one part overheats. Therefore, it is vital that the cooling system keep all parts at suitably
low temperatures. Liquid-cooled engines are able to vary the size of their passageways
through the engine block so that coolant flow may be tailored to the needs of each area.
Locations with either high peak temperatures (narrow islands around the combustion
chamber) or high heat flow (around exhaust ports) may require generous cooling. This
reduces the occurrence of hot spots, which are more difficult to avoid with air cooling. Air-
cooled engines may also vary their cooling capacity by using more closely spaced cooling
fins in that area, but this can make their manufacture difficult and expensive.
Only the fixed parts of the engine, such as the block and head, are cooled directly by the
main coolant system. Moving parts such as the pistons, and to a lesser extent the crank and
rods, must rely on the lubrication oil as a coolant, or to a very limited amount of conduction
into the block and thence the main coolant. High performance engines frequently have
additional oil, beyond the amount needed for lubrication, sprayed upwards onto the bottom of
the piston just for extra cooling. Air-cooled motorcycles often rely heavily on oil-cooling in
addition to air-cooling of the cylinder barrels.
Liquid-cooled engines usually have a circulation pump. The first engines relied on thermo-
syphon cooling alone, where hot coolant left the top of the engine block and passed to the
radiator, where it was cooled before returning to the bottom of the engine. Circulation was
powered by convection alone.
Other demands include cost, weight, reliability, and durability of the cooling system itself.
Conductive heat transfer is proportional to the temperature difference between materials. If
engine metal is at 250 °C and the air is at 20°C, then there is a 230°C temperature difference
for cooling. An air-cooled engine uses all of this difference. In contrast, a liquid-cooled engine
might dump heat from the engine to a liquid, heating the liquid to 135°C (Water's standard
boiling point of 100°C can be exceeded as the cooling system is both pressurised, and uses
a mixture with antifreeze) which is then cooled with 20°C air. In each step, the liquid-cooled
engine has half the temperature difference and so at first appears to need twice the cooling
area.
However, properties of the coolant (water, oil, or air) also affect cooling. As example,
comparing water and oil as coolants, one gram of oil can absorb about 55% of the heat for
the same rise in temperature (called the specific heat capacity). Oil has about 90% the
density of water, so a given volume of oil can absorb only about 50% of the energy of the
same volume of water. The thermal conductivity of water is about 4 times that of oil, which
can aid heat transfer. The viscosity of oil can be ten times greater than water, increasing the
energy required to pump oil for cooling, and reducing the net power output of the engine.
Comparing air and water, air has vastly lower heat capacity per gram and per volume (4000)
and less than a tenth the conductivity, but also much lower viscosity (about 200 times lower:
17.4 × 10−6Pa·s for air vs 8.94 × 10−4 Pa·s for water). Continuing the calculation from two
paragraphs above, air cooling needs ten times of the surface area, therefore the fins, and air
needs 2000 times the flow velocity and thus a recirculating air fan needs ten times the power
of a recirculating water pump. Moving heat from the cylinder to a large surface area for air
cooling can present problems such as difficulties manufacturing the shapes needed for good
heat transfer and the space needed for free flow of a large volume of air. Water boils at about
the same temperature desired for engine cooling. This has the advantage that it absorbs a
great deal of energy with very little rise in temperature (called heat of vaporization), which is
good for keeping things cool, especially for passing one stream of coolant over several hot
objects and achieving uniform temperature. In contrast, passing air over several hot objects
in series warms the air at each step, so the first may be over-cooled and the last under-
cooled. However, once water boils, it is an insulator, leading to a sudden loss of cooling
where steam bubbles form (for more, see heat transfer). Unfortunately, steam may return to
water as it mixes with other coolant, so an engine temperature gauge can indicate an
acceptable temperature even though local temperatures are high enough that damage is
being done.
An engine needs different temperatures. The inlet including the compressor of a turbo and in
the inlet trumpets and the inlet valves need to be as cold as possible. A countercurrent heat
exchange with forced cooling air does the job. The cylinder-walls should not heat up the air
before compression, but also not cool down the gas at the combustion. A compromise is a
wall temperature of 90°C. The viscosity of the oil is optimized for just this temperature. Any
cooling of the exhaust and the turbine of the turbocharger reduces the amount of power
available to the turbine, so the exhaust system is often insulated between engine and
turbocharger to keep the exhaust gases as hot as possible.
The temperature of the cooling air may range from well below freezing to 50°C. Further, while
engines in long-haul boat or rail service may operate at a steady load, road vehicles often
see widely varying and quickly varying load. Thus, the cooling system is designed to vary
cooling so the engine is neither too hot nor too cold. Cooling system regulation includes
adjustable baffles in the air flow (sometimes called 'shutters' and commonly run by a
pneumatic 'shutterstat); a fan which operates either independently of the engine, such as an
electric fan, or which has an adjustable clutch; a thermostatic valve or just 'thermostat' that
can block the coolant flow when too cool. In addition, the motor, coolant, and heat exchanger
have some heat capacity which smooths out temperature increase in short sprints. Some
engine controls shut down an engine or limit it to half throttle if it overheats. Modern
electronic engine controls adjust cooling based on throttle to anticipate a temperature rise,
and limit engine power output to compensate for finite cooling.
Finally, other concerns may dominate cooling system design. As example, air is a relatively
poor coolant, but air cooling systems are simple, and failure rates typically rise as the square
of the number of failure points. Also, cooling capacity is reduced only slightly by small air
coolant leaks. Where reliability is of utmost importance, as in aircraft, it may be a good trade-
off to give up efficiency, durability (interval between engine rebuilds), and quietness in order
to achieve slightly higher reliability — the consequences of a broken airplane engine are so
severe, even a slight increase in reliability is worth giving up other good properties to achieve
it.
Air-cooled and liquid-cooled engines are both used commonly. Each principle has
advantages and disadvantages, and particular applications may favor one over the other. For
example, most cars and trucks use liquid-cooled engines, while many small airplane and low-
cost engines are air-cooled.
[edit]Generalization difficulties
It is difficult to make generalizations about air-cooled and liquid-cooled engines. Air-
cooled Volkswagen kombis are known[who?] for rapid wear in normal use[citation needed] and
sometimes sudden failure when driven in hot weather. Alternatively, air-cooled Deutz diesel
engines are known for reliability even in extreme heat, and are often used in situations where
the engine runs unattended for months at a time.
Similarly, it is usually desirable to minimize the number of heat transfer stages in order to
maximize the temperature difference at each stage. However, Detroit Diesel 2-stroke cycle
engines commonly use oil cooled by water, with the water in turn cooled by air.
The coolant used in many liquid-cooled engines must be renewed periodically, and can
freeze at ordinary temperatures thus causing permanent engine damage. Air-cooled engines
do not require coolant service, and do not suffer engine damage from freezing, two
commonly cited advantages for air-cooled engines. However, coolant based on propylene
glycol is liquid to -55 °C, colder than is encountered by many engines; shrinks slightly when it
crystallizes, thus avoiding engine damage; and has a service life over 10,000 hours,
essentially the lifetime of many engines.
It is usually more difficult to achieve either low emissions or low noise from an air-cooled
engine, two more reasons most road vehicles use liquid-cooled engines. It is also often
difficult to build large air-cooled engines, so nearly all air-cooled engines are under
500 kW (670 hp), whereas large liquid-cooled engines exceed 80 MW (107000 hp) (Wärtsilä-
Sulzer RTA96-C 14-cylinder diesel).
[edit]Air-cooling
Further information: Air cooler
Cars and trucks using direct air cooling (without an intermediate liquid) were built over a long
period from the very beginning and ending with a small and generally unrecognized technical
change. BeforeWorld War II, water-cooled cars and trucks routinely overheated while
climbing mountain roads, creating geysers of boiling cooling water. This was considered
normal, and at the time, most noted mountain roads had auto repair shops to minister to
overheating engines.
ACS (Auto Club Suisse) maintains historical monuments to that era on the Susten
Pass where two radiator refill stations remain (See a picture here). These have instructions
on a cast metal plaque and a spherical bottom watering can hanging next to a water spigot.
The spherical bottom was intended to keep it from being set down and, therefore, be useless
around the house, in spite of which it was stolen, as the picture shows.
During that period, European firms such as Magirus-Deutz built air-cooled diesel trucks,
Porsche built air-cooled farm tractors,[2] and Volkswagen became famous with air-cooled
passenger cars. In the USA, Franklin built air-cooled engines. The Czechoslovakia based
company Tatra is known for their big size air-cooled V8 car engines, Tatra engineer Julius
Mackerle published a book on it. Air-cooled engines are better adapted to extremely cold and
hot environmental weather temperatures, you can see air-cooled engines starting and
running in freezing conditions that stuck water-cooled engines and continue working when
water-cooled ones start producing steam jets.
[edit]Liquid cooling
Today, most engines are liquid-cooled.[3][4][5]
A fully closed IC engine cooling system
Open IC engine cooling system
Semiclosed IC engine cooling system
Liquid cooling is also employed in maritime vehicles (vessels, ...). For vessels, the seawater
itself is mostly used for cooling. In some cases, chemical coolants are also employed (in
closed systems) or they are mixed with seawater cooling.[6][7]
[edit]Transition Away From Air Cooling
The change of air cooling to liquid cooling occurred at the start of World War II when the US
military needed reliable vehicles. The subject of boiling engines was addressed, researched,
and a solution found. Previous radiators and engine blocks were properly designed and
survived durability tests, but used water pumps with a leaky graphite-lubricated "rope" seal
(gland) on the pump shaft. The seal was inherited from steam engines, where water loss is
accepted, since steam engines already expend large volumes of water. Because the pump
seal leaked mainly when the pump was running and the engine was hot, the water loss
evaporated inconspicuously, leaving at best a small rusty trace when the engine stopped and
cooled, thereby not revealing significant water loss. Automobile radiators (or heat
exchangers) have an outlet that feeds cooled water to the engine and the engine has an
outlet that feeds heated water to the top of the radiator. Water circulation is aided by a rotary
pump that has only a slight effect, having to work over such a wide range of speeds that its
impeller has only a minimal effect as a pump. While running, the leaking pump seal drained
cooling water to a level where the pump could no longer return water to the top of the
radiator, so water circulation ceased and water in the engine boiled. However, since water
loss led to overheat and further water loss from boil-over, the original water loss was hidden.
After isolating the pump problem, cars and trucks built for the war effort (no civilian cars were
built during that time) were equipped with carbon-seal water pumps that did not leak and
caused no more geysers. Meanwhile, air cooling advanced in memory of boiling engines...
even though boil-over was no longer a common problem. Air-cooled engines became popular
throughout Europe. After the war, Volkswagen advertised in the USA as not boiling over,
even though new water-cooled cars no longer boiled over, but these cars sold well, and
without question. But as air quality awareness rose in the 1960s, and laws governing exhaust
emissions were passed, unleaded gas replaced leaded gas and leaner fuel mixtures became
the norm. These reductions in the cooling effects of both the lead and the formerly rich fuel
mixture, led to overheating in the air-cooled engines.[citation needed] Valve failures and other
engine damage was the result.[citation needed] Volkswagen responded by abandoning their (flat)
horizontally opposed air-cooled engines,[citation needed] while Subaru took a different course and
chose liquid-cooling for their (flat) engines.
Today practically no air-cooled automotive engines are built, air cooling being fraught with
manufacturing expense and maintenance problems. Motorcycles had an additional problem
in that a water leak presented a greater threat to reliability, their engines having small cooling
water volume, so they were loath to change; today most larger motorcycles are water-cooled
with many relying on convection circulation with no pump.
For the forty years following the first flight of the Wright brothers, airplanes used internal combustion engines to turnpropellers to generate thrust. Today, most general aviation or private airplanes are still powered by propellers and internal combustion engines, much like your automobile engine. We will discuss the fundamentals of the internal combustion engine using the Wright brothers' 1903 engine, shown in the figure, as an example. The brothers' design is very simple by today's standards, so it is a good engine for students to study and learn the fundamentals of engines and their operation. On this page we present a computer drawing of the lubrication system of the Wright brothers' 1903 aircraft engine.
Mechanical Operation
The figure at the top shows the major components of the lubrication system on the Wright 1903 engine. In any internal combustion engine, fuel and oxygen are combined in a combustion process to produce the power to turn the crankshaft of the engine. The combustion generates high pressure exhaust gas which exerts a force on the face of a piston. The piston moves inside a cylinder and is connected to the crankshaft by a rod which transmits the power. There are many moving parts is this power train as shown in this computer animation:
The job of the lubrication system is to distribute oil to the moving parts to reduce friction between surfaces which rub against each other.
The lubrication system used by the Wright brothers is quite simple. An oil pump is located on the bottom of the engine, at the left of the figure. The pump is driven by a worm gear off the main exhaust valve cam shaft. The oil is pumped to the top of the engine, at the right, inside a feed line. Small holes in the feed line allow the oil to drip inside the crankcase. In the figure, we have removed the fuel system and peeled back the covering of the crankcase to see inside. The oil drips onto the pistons as they move in the cylinders, lubricating the surface between the piston and cylinder. The oil then runs down inside the crankcase to the main bearings holding the crankshaft. Oil is picked up and splashed onto the bearings to lubricate these surfaces. Along the outside of the bottom of the crankcase is a collection tube which gathers up the used oil andreturns it to the oil pump to be circulated again. Notice that the brothers did not lubricate the valves and rocker assembly for the combustion chambers.
Difference between a turbocharger and a supercharger on a cars engine
Let's start with the similarities. Both turbochargers and superchargers are called forced
induction systems. They compress the air flowing into the engine (see How Car Engines
Work for a description of airflow in a normal engine). The advantage of compressing the air is
that it lets the engine stuff more air into a cylinder. More air means that more fuel can be
stuffed in, too, so you get more power from each explosion in each cylinder. A
turbo/supercharged engine produces more power overall than the same engine without the
charging.
The typical boost provided by either a turbocharger or a supercharger is 6 to 8 pounds per
square inch (psi). Since normal atmospheric pressure is 14.7 psi at sea level, you can see
that you are getting about 50-percent more air into the engine. Therefore, you would expect
to get 50-percent more power. It's not perfectly efficient, though, so you might get a 30-
percent to 40-percent improvement instead.
The key difference between a turbocharger and a supercharger is its power supply.
Something has to supply the power to run the air compressor. In a supercharger, there is
a belt that connects directly to the engine. It gets its power the same way that the water
pump or alternator does. A turbocharger, on the other hand, gets its power from the exhaust
stream. The exhaust runs through a turbine, which in turn spins the compressor (see How
Gas Turbine Engines Work for details).
There are tradeoffs in both systems. In theory, a turbocharger is more efficient because it is
using the "wasted" energy in the exhaust stream for its power source. On the other hand, a
turbocharger causes some amount of back pressure in the exhaust system and tends to
provide less boost until the engine is running at higher RPMs. Superchargers are easier to
install but tend to be more expensive.
Emission Standards
Emission standards are requirements that set specific limits to the amount
of pollutants that can be released into the environment. Many emissions standards
focus on regulating pollutants released by automobiles (motor cars) and other
powered vehicles but they can also regulate emissions from industry, power plants,
small equipment such as lawn mowers and diesel generators. Frequent policy
alternatives to emissions standards are technology standards (which mandate
Standards generally regulate the emissions of nitrogen oxides (NOx), sulfur
oxides, particulate matter (PM) or soot,carbon monoxide (CO), or
volatile hydrocarbons (see carbon dioxide equivalent).
Contents
[hide]
1 Vehicle Emission performance standard
2 Americas
o 2.1 USA
3 Europe
o 3.1 European Union
o 3.2 UK
o 3.3 Germany
4 Asia
o 4.1 China
o 4.2 Hong Kong
o 4.3 India
4.3.1 Background
4.3.2 Trucks and Buses
4.3.3 Light duty diesel vehicles
4.3.4 Light duty gasoline vehicles
4.3.4.1 4-wheel vehicles
4.3.4.2 3- and 2-wheel vehicles
4.3.5 Overview of the emission norms in India by CDR
o 4.4 Japan
5 See also
6 References
7 External links
o 7.1 EU
[edit]Vehicle Emission performance standard
This section needs additional citations for verification. Please help improve
this article by adding citations to reliable sources. Unsourced material may
be challenged and removed. (January 2009)
An emission performance standard is a limit that sets thresholds above which a
different type of emission control technology might be needed. While emission
performance standards have been used to dictate limits for
conventional pollutants such as oxides of nitrogen and oxides of sulfur (NOx and
SOx),[1] this regulatory technique may be used to regulate greenhouse gasses,
particularlycarbon dioxide (CO2). In the US, this is given in pounds of carbon dioxide
per megawatt-hour (lbs. CO2/MWhr), and kilograms CO2/MWhr elsewhere in the
world...
[edit]Americas
This section requires expansion.
[edit]USAMain article: United States emission standards
In the United States, emissions standards are managed by the Environmental
Protection Agency (EPA). The state of California has special dispensation to
promulgate more stringent vehicle emissions standards, and other states may choose
to follow either the national or California standards.
California's emissions standards are set by the California Air Resources Board, known
locally by its acronym "CARB". Given that California's automotive market is one of the
largest in the world, CARB wields enormous influence over the emissions
requirements that major automakers must meet if they wish to sell into that market. In
addition, several other U.S. states also choose to follow the CARB standards, so their
rulemaking has broader implications within the U.S. How Stuff Works: CARB lists 16
other states adopting CARB rules as of mid 2009. CARB's policies have also
influenced EU emissions standards.
Federal (National) "Tier 1" regulations went into effect starting in 1994, and "Tier 2"
standards are being phased in from 2004 to 2009. Automobiles and light
trucks (SUVs, pickup trucks, and minivans) are treated differently under certain
standards.
California is attempting to regulate greenhouse gas emissions from automobiles, but
faces a court challenge from the federal government. The states are also attempting
to compel the federal EPA to regulate greenhouse gas emissions, which as of 2007 it
has declined to do. On May 19, 2009 news reports indicate that the Federal EPA will
largely adopt California's standards on greenhouse gas emissions.
California and several other western states have passed bills requiring performance-
based regulation of greenhouse gases from electricity generation.
In an effort to decrease emissions from heavy-duty diesel engines faster,
the California Air Resources Board's Carl Moyer Program funds upgrades that are in
advance of regulations.
The EPA has separate regulations for small engines, such as groundskeeping
equipment. The states must also promulgate miscellaneous emissions regulations in
order to comply with the National Ambient Air Quality Standards.
Europe
European UnionMain article: European emission standards
The European Union has its own set of emissions standards that all new vehicles
must meet. Currently, standards are set for all road vehicles, trains, barges and
'nonroad mobile machinery' (such as tractors). No standards apply to seagoing ships
or airplanes. The emissions standards change based on the test cycle used: ECE R49
(old) and ESC (European Steady Cycle, since 2000).
Currently there are no standards for CO2 emissions. The European Parliament has
suggested introducing mandatory CO2 emission standards[2] to replace current
voluntary commitments by the auto manufacturers (see ACEA agreement) and
labeling. In late 2005, the European Commission started working on a proposal for a
new law to limit CO2 emissions from cars.[3] The European Commission has received
support of the European Parliament for its proposal to promote a broad market
introduction of clean and energy efficient vehicles through public procurement.[4]
The EU is to introduce Euro 4 effective January 1, 2008, Euro 5 effective January 1,
2010 and Euro 6 effective January 1, 2014. These dates have been postponed for two
years to give oil refineries the opportunity to modernize their plants.
UK
The British Parliament proposed legislation regulating CO2 emissions from electricity
generation via emission performance standards.[5] This bill was even more stringent
than that of the western American states in that it limited production to the equivalent
of 400 kg CO2/MWh, which would effectively preclude the construction of any
traditional coal-fired power plants.
Germany
According to the German federal automotive office 37.3 % (15.4 million) cars in
Germany (total car population 41.3 million) conform to the Euro 4 standard from Jan
2009.
Due to rapidly expanding wealth and prosperity, the number of coal power plants and
cars on China's roads is rapidly growing, creating an ongoing pollution problem. China
enacted its first emissions controls on automobiles in 2000, equivalent to Euro I
standards. China's State Environmental Protection Administration (SEPA) upgraded
emission controls again on July 1, 2004 to the Euro II standard.[6] More stringent
emission standard, National Standard III, equivalent to Euro III standards, went into
effect on July 1, 2007.[7] Plans are for Euro IV standards to take effect in 2010. Beijing
introduced the Euro IV standard in advance on January 1, 2008, became the first city
in mainland China to adopt this standard.[8]
Hong Kong
From Jan 1, 2006, all new passenger cars with spark-ignition engines in Hong
Kong must meet either Euro IV petrol standard, Japanese Heisei 17 standard or US
EPA Tier 2 Bin 5 standard. For new passenger cars with compression-ignition
engines, they must meet US EPA Tier 2 Bin 5 standard.
Background
The first Indian emission regulations were idle emission limits which became effective
in 1989. These idle emission regulations were soon replaced by mass emission limits
for both petrol (1991) and diesel (1992) vehicles, which were gradually tightened
during the 1990s. Since the year 2000, India started adopting European emission and
fuel regulations for four-wheeled light-duty and for heavy-dc. Indian own emission
regulations still apply to two- and three-wheeled vehicles.
Current requirement is that all transport vehicles carry a fitness certificate that is
renewed each year after the first two years of new vehicle registration.
On October 6, 2003, the National Auto Fuel Policy has been announced, which
envisages a phased program for introducing Euro 2 - 4 emission and fuel regulations
by 2010. The implementation schedule of EU emission standards in India is
summarized in Table 1.[9]
Table 1: Indian Emission Standards (4-Wheel Vehicles)
Standard Reference Date Region
India 2000 Euro 1 2000 Nationwide
Bharat Stage II Euro 2
2001 NCR*, Mumbai, Kolkata, Chennai
2003.04 NCR*, 12 Cities†
2005.04 Nationwide
Bharat Stage III Euro 3
2005.04 NCR*, 12 Cities†
2010.04 Nationwide
Bharat Stage IV Euro 4 2010.04 NCR*, 12 Cities†
* National Capital Region (Delhi)
† Mumbai, Kolkata, Chennai, Bengaluru, Hyderabad, Ahmedabad, Pune, Surat, Kanpur, Lucknow, Sholapur, and Agra
The above standards apply to all new 4-wheel vehicles sold and registered in the
respective regions. In addition, the National Auto Fuel Policy introduces certain
emission requirements for interstate buses with routes originating or terminating in
Delhi or the other 10 cities.
For 2-and 3-wheelers, Bharat Stage II (Euro 2) will be applicable from April 1, 2005
and Stage III (Euro 3) standards would come in force preferably from April 1, 2008,
but not later than April 1, 2010.[10]
[edit]Trucks and Buses
Emission standards for new heavy-duty diesel engines—applicable to vehicles of GVW > 3,500 kg—
are listed in Table 1. Emissions are tested over the ECE R49 13-mode test (through the Euro II stage)
Table 2 Emission Standards for Diesel Truck and Bus Engines,
g/kWh
Year Reference CO HC NOx PM
1992 - 17.3-32.6 2.7-3.7 - -
1996 - 11.20 2.40 14.4 -
2000 Euro I 4.5 1.1 8.0 0.36*
2005† Euro II 4.0 1.1 7.0 0.15
2010† Euro III 2.1 0.66 5.0 0.10
* 0.612 for engines below 85 kW
† earlier introduction in selected regions, see Table 1
More details on Euro I-III regulations can be found in the EU heavy-duty engine
standards page.
[edit]Light duty diesel vehicles
Emission standards for light-duty diesel vehicles (GVW ≤ 3,500 kg) are summarized in Table 3.
Ranges of emission limits refer to different classes (by reference mass) of light commercial vehicles;
compare the EU light-duty vehicle emission standards page for details on the Euro 1 and later
standards. The lowest limit in each range applies to passenger cars (GVW ≤ 2,500 kg; up to 6 seats).
Table 3 Emission Standards for Light-Duty Diesel Vehicles, g/km
Year Reference CO HC HC+NOx PM
1992 - 17.3-32.6 2.7-3.7 - -
1996 - 5.0-9.0 - 2.0-4.0 -
2000 Euro 1 2.72-6.90 - 0.97-1.70 0.14-0.25
2005† Euro 2 1.0-1.5 - 0.7-1.2 0.08-0.17
The test cycle has been the ECE + EUDC for low power vehicles (with maximum
speed limited to 90 km/h). Before 2000, emissions were measured over an Indian test
cycle.
Engines for use in light-duty vehicles can be also emission tested using an engine dynamometer. The
respective emission standards are listed in Table 4.
Table 4 Emission Standards for Light-Duty Diesel Engines, g/kWh
Year Reference CO HC NOx PM
1992 - 14.0 3.5 18.0 -
1996 - 11.20 2.40 14.4 -
2000 Euro I 4.5 1.1 8.0 0.36*
2005† Euro II 4.0 1.1 7.0 0.15
* 0.612 for engines below 85 kW
† earlier introduction in selected regions, see Table 1
[edit]Light duty gasoline vehicles
[edit]4-wheel vehicles
Emissions standards for gasoline vehicles (GVW ≤ 3,500 kg) are summarized in Table 5. Ranges of
emission limits refer to different classes of light commercial vehicles (compare the EU light-duty
vehicle emission standards page). The lowest limit in each range applies to passenger cars (GVW ≤
2,500 kg; up to 6 seats).
Table 5 Emission Standards for Gasoline Vehicles (GVW ≤ 3,500 kg), g/km
Year Reference CO HC HC+NOx
1991 - 14.3-27.1 2.0-2.9 -
1996 - 8.68-12.4 - 3.00-4.36
1998* - 4.34-6.20 - 1.50-2.18
2000 Euro 1 2.72-6.90 - 0.97-1.70
2005† Euro 2 2.2-5.0 - 0.5-0.7
* for catalytic converter fitted vehicles
† earlier introduction in selected regions, see Table 1
Gasoline vehicles must also meet an evaporative (SHED) limit of 2 g/test (effective
2000).
[edit]3- and 2-wheel vehicles
Emission standards for 3- and 2-wheel gasoline vehicles are listed in the following
tables.[11]
Table 6 Emission Standards for 3-Wheel Gasoline Vehicles, g/km
Year CO HC HC+NOx
1991 12-30 8-12 -
1996 6.75 - 5.40
2000 4.00 - 2.00
2005 (BS II) 2.25 - 2.00
Table 7 Emission Standards for 2-Wheel Gasoline Vehicles, g/km
Year CO HC HC+NOx
1991 12-30 8-12 -
1996 5.50 - 3.60 4.60
[edit]Overview of the emission norms in India by CDR
1991 - Idle CO Limits for Gasoline Vehicles and Free Acceleration Smoke for
Diesel Vehicles, Mass Emission Norms for Gasoline Vehicles.
1992 - Mass Emission Norms for Diesel Vehicles.
1996 - Revision of Mass Emission Norms for Gasoline and Diesel Vehicles,
mandatory fitment of Catalytic Converter for Cars in Metros on Unleaded Gasoline.
1998 - Cold Start Norms Introduced .
2000 - India 2000 (Eq. to Euro I) Norms, Modified IDC (Indian Driving Cycle),
Bharat Stage II Norms for Delhi.
2001 - Bharat Stage II (Eq. to Euro II) Norms for All Metros, Emission Norms for
CNG & LPG Vehicles.
2003 - Bharat Stage II (Eq. to Euro II) Norms for 11 major cities.
2005 - From 1 April Bharat Stage III (Eq. to Euro III) Norms for 11 major cities.
2010 - Bharat Stage III Emission Norms for 4-wheelers for entire country
whereas Bharat Stage - IV (Eq. to Euro IV) for 13 major cities. Bharat Stage IV
also has norms on OBD (similar to Euro III but diluted)
[edit]Japan
Background
In 1973 the first installment of four sets of new emissions standards were introduced.
Interim standards were introduced on January 1, 1975 and again for 1976. The final
set of standards were introduced for 1978.[12] While the standards were introduced
they were not made immediately mandatory, instead tax breaks were offered for cars
which passed them.[13] The standards were based on those adopted by the original US
Clean Air Act of 1970, but the test cycle included more slow city driving to correctly
reflect the Japanese situation.[14] The 1978 limits for mean emissions during a "Hot
Start Test" of CO, hydrocarbons, and NOx were 2.1 grams per kilometre (0.00 g/mi) of
CO, .25 grams per kilometre (0.00 g/mi) of HC, and .25 grams per kilometre
(0.00 g/mi) of NOx respectively.[14]Maximum limits are 2.7 grams per kilometre
(0.00 g/mi) of CO, .39 grams per kilometre (0.00 g/mi) of HC, and .48 grams per
kilometre (0.00 g/mi) of NOx. The "10 - 15 Mode Hot Cycle" test, used to determine
individual fuel economy ratings and emissions observed from the vehicle being tested,
use a specific testing regime. [15][16][17]
In 1992, to cope with NOx pollution problems from existing vehicle fleets in highly
populated metropolitan areas, the Ministry of the Environment adopted the “Law
Concerning Special Measures to Reduce the Total Amount of Nitrogen Oxides
Emitted from Motor Vehicles in Specified Areas”, called in short The Motor Vehicle
NOx Law. The regulation designated a total of 196 communities in the Tokyo,
Saitama, Kanagawa, Osaka and Hyogo Prefectures as areas with significant air
pollution due to nitrogen oxides emitted from motor vehicles. Under the Law, several
measures had to be taken to control NOx from in-use vehicles, including enforcing
emission standards for specified vehicle categories.
The regulation was amended in June 2001 to tighten the existing NOx requirements
and to add PM control provisions. The amended rule is called the “Law Concerning
Special Measures to Reduce the Total Amount of Nitrogen Oxides and Particulate
Matter Emitted from Motor Vehicles in Specified Areas”, or in short the Automotive
NOx and PM Law.
Emission Standards
The NOx and PM Law introduces emission standards for specified categories of in-
use highway vehicles including commercial goods (cargo) vehicles such as trucks and
vans, buses, and special purpose motor vehicles, irrespective of the fuel type. The
regulation also applies to diesel powered passenger cars (but not to gasoline cars).
In-use vehicles in the specified categories must meet 1997/98 emission standards for
the respective new vehicle type (in the case of heavy duty engines NOx = 4.5 g/kWh,
PM = 0.25 g/kWh). In other words, the 1997/98 new vehicle standards are
retroactively applied to older vehicles already on the road. Vehicle owners have two
methods to comply:
1. Replace old vehicles with newer, cleaner models
2. Retrofit old vehicles with approved NOx and PM control devices
Vehicles have a grace period, between 9 and 12 years from the initial registration, to
comply. The grace period depends on the vehicle type, as follows:
Light commercial vehicles (GVW ≤ 2500 kg): 8 years
Heavy commercial vehicles (GVW > 2500 kg): 9 years
Micro buses (11-29 seats): 10 years
Large buses (≥ 30 seats): 12 years
Special vehicles (based on a cargo truck or bus): 10 years
Diesel passenger cars: 9 years
Furthermore, the regulation allows fulfillment of its requirements to be postponed by
an additional 0.5-2.5 years, depending on the age of the vehicle. This delay was
introduced in part to harmonize the NOx and PM Law with the Tokyo diesel retrofit
program.
The NOx and PM Law is enforced in connection with Japanese vehicle inspection
program, where non-complying vehicles cannot undergo the inspection in the
designated areas. This, in turn, may trigger an injunction on the vehicle operation
under the Road Transport Vehicle Law.
Vehicle emissions control is the study and practice of reducing the motor vehicle
emissions -- emissions produced by motor vehicles, especially internal combustion
engines.
Emissions of many air pollutants have been shown to have variety of negative
effects on public health and the natural environment. Emissions that are principal
pollutants of concern include:
Hydrocarbons - A class of burned or partially burned fuel, hydrocarbons
are toxins. Hydrocarbons are a major contributor to smog, which can be a major
problem in urban areas. Prolonged exposure to hydrocarbons contributes
to asthma, liver disease, , lung disease, and cancer. Regulations governing
hydrocarbons vary according to type of engine and jurisdiction; in some cases,
"non-methane hydrocarbons" are regulated, while in other cases, "total
hydrocarbons" are regulated. Technology for one application (to meet a non-
methane hydrocarbon standard) may not be suitable for use in an application that
has to meet a total hydrocarbon standard. Methane is not directly toxic, but is more
difficult to break down in a catalytic converter, so in effect a "non-methane
hydrocarbon" regulation can be considered easier to meet. Since methane is
a greenhouse gas, interest is rising in how to eliminate emissions of it.
Carbon monoxide (CO) - A product of incomplete combustion, carbon monoxide
reduces the blood's ability to carry oxygen; overexposure (carbon monoxide
poisoning) may be fatal. Carbon Monoxide poisoning is a major killer.
Nitrogen oxides (NOx) - Generated when nitrogen in the air reacts with oxygen
at the high temperature and pressure inside the engine. NOx is a precursor to
smog and acid rain. NOx is a mixture of NO, N2O, and NO2. NO2 is extremely
reactive. It destroys resistance to respiratory infection. NOx production is increased
when an engine runs at its most efficient (i.e. hottest) part of the cycle.
Particulate matter – Soot or smoke made up of particles in the micrometre size
range: Particulate matter causes negative health effects, including but not limited
to respiratory disease and cancer.
Sulfur oxide (SOx) - A general term for oxides of sulfur, which are emitted from
motor vehicles burning fuel containing sulfur. Reducing the level of fuel sulfur
reduces the level of Sulfur oxide emitted from the tailpipe. Refineries generally fight
requirements to do this because of the increased costs to them, ignoring the
increased costs to society as a whole.
Volatile organic compounds (VOCs) - Organic compounds which typically have
a boiling point less than or equal to 250 °C; for
example chlorofluorocarbons (CFCs) and formaldehyde. Volatile organic
compounds are a subsection of Hydrocarbons that are mentioned separately
because of their dangers to public health.
History
Throughout the 1950s and 1960s, various federal, state and local governments in
the United States conducted studies into the numerous sources of air pollution. These
studies ultimately attributed a significant portion of air pollution to the automobile, and
concluded air pollution is not bounded by local political boundaries. At that time, such
minimal emission control regulations as existed in the U.S. were promulgated at the
municipal or, occasionally, the state level. The ineffective local regulations were
gradually supplanted by more comprehensive state and federal regulations. By 1967
theState of California created the California Air Resources Board, and in 1970, the
federal United States Environmental Protection Agency was established. Both
agencies, as well as other state agencies, now create and enforce emission
regulations for automobiles in the United States. Similar agencies and regulations
were contemporaneously developed and implemented in Canada, Western
Europe,Australia, and Japan.
The first effort at controlling pollution from automobiles was the PCV (positive
crankcase ventilation) system. This draws crankcase fumes heavy in unburned
hydrocarbons — a precursor tophotochemical smog — into the engine's intake tract
so they are burned rather than released unburned from the crankcase into the
atmosphere. Positive crankcase ventilation was first installed on a widespread basis
by law on all new 1961-model cars first sold in California. The following year, New
York required it. By 1964, most new cars sold in the U.S. were so equipped, and PCV
quickly became standard equipment on all vehicles worldwide.[1]
The first legislated exhaust (tailpipe) emission standards were promulgated by the
State of California for 1966 model year for cars sold in that state, followed by the
United States as a whole in model year 1968. The standards were progressively
tightened year by year, as mandated by the EPA.
By the 1974 model year, the emission standards had tightened such that the de-
tuning techniques used to meet them were seriously reducing engine efficiency and
thus increasing fuel usage. The new emission standards for 1975 model year, as well
as the increase in fuel usage, forced the invention of the catalytic converter for after-
treatment of the exhaust gas. This was not possible with existingleaded gasoline,
because the lead residue contaminated the platinum catalyst. In 1972, General
Motors proposed to the American Petroleum Institute the elimination of leaded fuels
for 1975 and later model year cars. The production and distribution of unleaded fuel
was a major challenge, but it was completed successfully in time for the 1975 model
year cars. All modern cars are now equipped with catalytic converters and leaded fuel
is nearly impossible to buy in most First World countries.
[edit]Regulatory agencies
The agencies charged with regulating exhaust emissions vary from jurisdiction to
jurisdiction, even in the same country. For example, in the United States, overall
responsibility belongs to the EPA, but due to special requirements of the State of
California, emissions in California are regulated by the Air Resources Board. In Texas,
the Texas Railroad Commission is responsible for regulating emissions from LPG-
fueled rich burn engines (but not gasoline-fueled rich burn engines).
[edit]North America
California Air Resources Board - California, United States (most sources)
Environment Canada - Canada (most sources)
Environmental Protection Agency - United States (most sources)
Texas Railroad Commission - Texas, United States (LPG-fueled engines only)
Transport Canada - Canada (trains and ships)
[edit]Europe
Ultimately, the European Union has control over regulation of emissions in EU
member states; however, many member states have their own government bodies to
enforce and implement these regulations in their respective countries. In short, the EU
forms the policy (by setting limits such as the European emission standard) and the
member states decide how to best implement it in their own country.
[edit]United Kingdom
In the United Kingdom, matters concerning environmental policy are what is known as
"devolved powers" which means, each of the constituent countries deals with it
separately through their own government bodies set up to deal with environmental
issues in their respective country:
Environment Agency - England and Wales
Scottish Environment Protection Agency (SEPA) - Scotland
Department of the Environment - Northern Ireland
However, many UK-wide policies are handled by the Department of the Environment
Food and Rural Affairs (DEFRA) and they are still subject to EU regulations.
[edit]Emissions control
Engine efficiency has been steadily improved with improved engine design, more
precise ignition timing and electronic ignition, more precise fuel metering,
and computerized engine management.
Advances in engine and vehicle technology continually reduce the toxicity of exhaust
leaving the engine, but these alone have generally been proved insufficient to meet
emissions goals. Therefore, technologies to detoxify the exhaust are an essential part
of emissions control.
[edit]Air injectionMain article: Secondary air injection
One of the first-developed exhaust emission control systems is secondary air
injection. Originally, this system was used to inject air into the engine's exhaust ports
to provide oxygen so unburned and partially-burned hydrocarbons in the exhaust
would finish burning. Air injection is now used to support the catalytic converter's
oxidation reaction, and to reduce emissions when an engine is started from cold. After
a cold start, an engine needs a fuel-air mixture richer than what it needs at operating
temperature, and the catalytic converter does not function efficiently until it has
reached its own operating temperature. The air injected upstream of the converter
supports combustion in the exhaust headpipe, which speeds catalyst warmup and
reduces the amount of unburned hydrocarbon emitted from the tailpipe.
Air Injection is a secondary technology, used in support of the main technologies on
some engines.
[edit]Exhaust gas recirculationMain article: Exhaust gas recirculation
In the United States and Canada, many engines in 1973 and newer vehicles (1972
and newer in California) have a system that routes a metered amount of exhaust into
the intake tract under particular operating conditions. Exhaust neither burns nor
supports combustion, so it dilutes the air/fuel charge to reduce peak combustion
chamber temperatures. This, in turn, reduces the formation of NOx.
[edit]Catalytic converterMain article: Catalytic converter
The catalytic converter is a device placed in the exhaust pipe, which converts
hydrocarbons, carbon monoxide, and NOx into less harmful gases by using a
combination of platinum, palladium and rhodium as catalysts.
There are two types of catalytic converter, a two-way and a three-way converter. Two-
way converters were common until the 1980s, when three-way converters replaced
them on most automobile engines. See the catalytic converter article for further
details.
[edit]Evaporative emissions control
"EVAP" redirects here. EVAP may also refer to Evaporation.
Evaporative emissions are the result of gasoline vapors escaping from the vehicle's
fuel system. Since 1971, all U.S. vehicles have had fully sealed fuel systems that do
not vent directly to the atmosphere; mandates for systems of this type appeared
contemporaneously in other jurisdictions. In a typical system, vapors from the fuel
tank and carburetor bowl vent (on carbureted vehicles) are ducted to canisters
containing activated carbon. The vapors are adsorbed within the canister, and during
certain engine operational modes fresh air is drawn through the canister, pulling the
vapor into the engine,where it burns.
[edit]Emission testing
In 1966, the first emission test cycle was enacted in the State of California measuring
tailpipe emissions in PPM (parts per million).
Some cities are also using a technology developed by Dr. Donald Stedman of
the University of Denver, which uses lasers to detect emissions while vehicles pass by
on public roads, thus eliminating the need for owners to go to a test center. Stedman's
laser detection of exhaust gases is commonly used in metropolitan areas.[2]
[edit]Use of emission test data
Emission test results from individual vehicles are in many cases compiled to evaluate
the emissions performance of various classes of vehicles, the efficacy of the testing
program and of various other emission-related regulations (such as changes to fuel
formulations) and to model the effects of auto emissions on public health and the
environment. For example, the Environmental Working Groupused California ASM
emissions data to create an "Auto Asthma Index" that rates vehicle models according
to emissions of hydrocarbons and nitrogen oxides, chemical precursors
to photochemical smog.
Catalytic convertor
A catalytic converter (colloquially, "cat" or "catcon") is a device used to convert
toxic exhaust emissions from an internal combustion engine into non-toxic
substances. Inside a catalytic converter, a catalyst stimulates a chemical reaction in
which noxious byproducts of combustion are converted to less toxic substances by
dint of catalysed chemical reactions. The specific reactions vary with the type of
catalyst installed. Most present-day vehicles that run ongasoline are fitted with a
"three way" converter, so named because it converts the three main pollutants in
automobile exhaust: an oxidising reaction convertscarbon monoxide (CO)
and unburned hydrocarbons (HC), and a reduction reaction converts oxides of
nitrogen (NOx) to produce carbon dioxide (CO2), nitrogen(N2), and water (H2O).[1]
The first widespread introduction of catalytic converters was in the United
States market, where 1975 model year automobiles were so equipped to comply with
tightening U.S. Environmental Protection Agency regulations on automobile exhaust
emissions. The catalytic converters fitted were two-way models, combining carbon
monoxide (CO) and unburned hydrocarbons (HC) to produce carbon dioxide (CO2)
and water (H2O). Two-way catalytic converters of this type are now considered
obsolete except on lean burn engines.[citation needed] Since most vehicles at the time
used carburetors that provided a relatively richair-fuel ratio, oxygen (O2) levels in the
exhaust stream were in general insufficient for the catalytic reaction to occur.
Therefore, most such engines were also equipped with secondary air
injection systems to induct air into the exhaust stream to allow the catalyst to function.
Catalytic converters are still most commonly used on automobile exhaust systems,
but are also used on generator sets, forklifts, mining
equipment, trucks,buses, locomotives, airplanes and other engine fitted devices. This
is usually in response to government regulation, either through direct environmental
regulation or through Health and Safety regulations.
Construction
Metal-core converter
Ceramic-core converter
The catalytic converter consists of several components:
1. The catalyst core, or substrate. For automotive catalytic converters, the core is
usually a ceramic monolith with a honeycomb structure. Metallic foil monoliths
made of FeCrAl are used in some applications. This is partially a cost issue.
Ceramic cores are inexpensive when manufactured in large quantities. Metallic
cores are less expensive to build in small production runs. Either material is
designed to provide a high surface area to support the catalyst washcoat, and
therefore is often called a "catalyst support".[citation needed] The cordierite ceramic
substrate used in most catalytic converters was invented by Rodney
Bagley, Irwin Lachman and Ronald Lewis at Corning Glass, for which they
were inducted into the National Inventors Hall of Fame in 2002.[citation needed]
2. The washcoat. A washcoat is a carrier for the catalytic materials and is used to
disperse the materials over a high surface area. Aluminum oxide,Titanium
dioxide, Silicon dioxide, or a mixture of silica and alumina can be used. The
catalytic materials are suspended in the washcoat prior to applying to the core.
Washcoat materials are selected to form a rough, irregular surface, which
greatly increases the surface area compared to the smooth surface of the bare
substrate. This maximizes the catalytically active surface available to react with
the engine exhaust.
3. The catalyst itself is most often a precious metal. Platinum is the most active
catalyst and is widely used, but is not suitable for all applications because of
unwanted additional reactions[vague] and high cost. Palladium and rhodium are
two other precious metals used. Rhodium is used as areduction catalyst,
palladium is used as an oxidation catalysts, and platinum is used both for
reduction and oxidation. Cerium, iron, manganese andnickel are also used,
although each has its own limitations. Nickel is not legal for use in the
European Union (because of its reaction with carbon monoxide into nickel
tetracarbonyl). Copper can be used everywhere except North America,[clarification
needed] where its use is illegal because of the formation of dioxin.
[edit]Types
[edit]Two-way
A two-way (or "oxidation") catalytic converter has two simultaneous tasks:
1. Oxidation of carbon monoxide to carbon dioxide: 2CO + O2 → 2CO2
2. Oxidation of hydrocarbons (unburnt and partially-burnt fuel) to carbon dioxide
and water: CxH2x+2 + [(3x+1)/2] O2 → xCO2 + (x+1) H2O (a combustion reaction)
This type of catalytic converter is widely used on diesel engines to reduce
hydrocarbon and carbon monoxide emissions. They were also used on gasoline
engines in American- and Canadian-market automobiles until 1981. Because of their
inability to control oxides of nitrogen, they were superseded by three-way converters.
[edit]Three-way
Since 1981, three-way (oxidation-reduction) catalytic converters have been used in
vehicle emission control systems in the United States and Canada; many other
countries have also adopted stringentvehicle emission regulations that in effect
require three-way converters on gasoline-powered vehicles. A three-way catalytic
converter has three simultaneous tasks:
1. Reduction of nitrogen oxides to nitrogen and oxygen: 2NOx → xO2 + N2
2. Oxidation of carbon monoxide to carbon dioxide: 2CO + O2 → 2CO2
3. Oxidation of unburnt hydrocarbons (HC) to carbon dioxide and water: CxH2x+2 +
[(3x+1)/2]O2 → xCO2 + (x+1)H2O
These three reactions occur most efficiently when the catalytic converter receives
exhaust from an engine running slightly above the stoichiometric point. This point is
between 14.6 and 14.8 parts air to 1 part fuel, by weight, for gasoline. The ratio
for Autogas (or liquefied petroleum gas (LPG)), natural gas and ethanol fuels is each
slightly different, requiring modified fuel system settings when using those fuels. In
general, engines fitted with 3-way catalytic converters are equipped with
a computerized closed-loop feedback fuel injection system using one or more oxygen
sensors, though early in the deployment of three-way
converters, carburetors equipped for feedback mixture control were used.
Three-way catalysts are effective when the engine is operated within a narrow band of
air-fuel ratios near stoichiometry, such that the exhaust gas oscillates between rich
(excess fuel) and lean (excess oxygen) conditions. However, conversion efficiency
falls very rapidly when the engine is operated outside of that band of air-fuel ratios.
Under lean engine operation, there is excess oxygen and the reduction of NOx is not
favored. Under rich conditions, the excess fuel consumes all of the available oxygen
prior to the catalyst, thus only stored oxygen is available for the oxidation function.
Closed-loop control systems are necessary because of the conflicting requirements
for effective NOx reduction and HC oxidation. The control system must prevent the
NOx reduction catalyst from becoming fully oxidized, yet replenish the oxygen storage
material to maintain its function as an oxidation catalyst.
[edit]Oxygen storage
Three-way catalytic converters can store oxygen from the exhaust gas stream, usually
when the air-fuel ratio goes lean.[6] When insufficient oxygen is available from the
exhaust stream, the stored oxygen is released and consumed (see cerium(IV) oxide).
A lack of sufficient oxygen occurs either when oxygen derived from NOx reduction is
unavailable or when certain maneuvers such as hard acceleration enrich the mixture
beyond the ability of the converter to supply oxygen.
[edit]Unwanted reactions
Unwanted reactions can occur in the three-way catalyst, such as the formation of
odoriferous hydrogen sulfide and ammonia. Formation of each can be limited by
modifications to the washcoat and precious metals used. It is difficult to eliminate
these byproducts entirely. Sulfur-free or low-sulfur fuels eliminate or reduce hydrogen
sulfide.
For example, when control of hydrogen-sulfide emissions is
desired, nickel or manganese is added to the washcoat. Both substances act to block
the absorption of sulfur by the washcoat. Hydrogen sulfide is formed when the
washcoat has absorbed sulfur during a low-temperature part of the operating cycle,
which is then released during the high-temperature part of the cycle and the sulfur
combines with HC.
[edit]For diesel engines
For compression-ignition (i.e., diesel engines), the most-commonly-used catalytic
converter is the Diesel Oxidation Catalyst (DOC). This catalyst uses O2 (oxygen) in
the exhaust gas stream to convert CO (carbon monoxide) to CO2 (carbon dioxide) and
HC (hydrocarbons) to H2O (water) and CO2. These converters often operate at 90
percent efficiency, virtually eliminating diesel odor and helping to reduce
visible particulates (soot). These catalyst are not active for NOx reduction because any
reductant present would react first with the high concentration of O2 in diesel exhaust
gas.
Reduction in NOx emissions from compression-ignition engine has previously been
addressed by the addition of exhaust gas to incoming air charge, known as exhaust
gas recirculation (EGR). In 2010, most light-duty diesel manufactures in the U.S.
added catalytic systems to their vehicles to meet new federal emissions requirements.
There are two techniques that have been developed for the catalytic reduction of
NOx emissions under lean exhaust condition - selective catalytic reduction (SCR) and
the lean NOx trap or NOx adsorber. Instead of precious metal-containing NOx
adsorbers, most manufacturers selected base-metal SCR systems that use
a reagent such as ammonia to reduce the NOx into nitrogen. Ammonia is supplied to
the catalyst system by the injection of urea into the exhaust, which then undergoes
thermal decomposition and hydrolysis into ammonia. One trademark product of urea
solution, also referred to as Diesel Emission Fluid (DEF), is AdBlue.
Diesel exhaust contains relatively high levels of particulate matter (soot), consisting in
large part of elemental carbon. Catalytic converters cannot clean up elemental
carbon, though they do remove up to 90 percent of the soluble organic fraction[citation
needed], so particulates are cleaned up by a soot trap or diesel particulate filter (DPF). A
DPF consists of a Cordierite or Silicon Carbide substrate with a geometry that forces
the exhaust flow through the substrate walls, leaving behind trapped soot particles. As
the amount of soot trapped on the DPF increases, so does the back pressure in the
exhaust system. Periodic regenerations (high temperature excursions) are required to
initiate combustion of the trapped soot and thereby reducing the exhaust back
pressure. The amount of soot loaded on the DPF prior to regeneration may also be
limited to prevent extreme exotherms from damaging the trap during regeneration. In
the U.S., all on-road light, medium and heavy-duty vehicles powered by diesel and
built after January 1, 2007, must meet diesel particulate emission limits that means
they effectively have to be equipped with a 2-Way catalytic converter and a diesel
particulate filter. Note that this applies only to the diesel engine used in the vehicle. As
long as the engine was manufactured before January 1, 2007, the vehicle is not
required to have the DPF system. This led to an inventory runup by engine
manufacturers in late 2006 so they could continue selling pre-DPF vehicles well into
2007.[7]
[edit]Lean Burn Spark Ignition Engines
For Lean Burn spark-ignition engines, an oxidation catalyst is used in the same
manner as in a diesel engine. Emissions from Lean Burn Spark Ignition Engines are
very similar to emissions from a Diesel Compression Ignition engine.
[edit]Installation
Many vehicles have a close-coupled catalysts located near the engine's exhaust
manifold. This unit heats up quickly due to its proximity to the engine, and reduces
cold-engine emissions by burning off hydrocarbons from the extra-rich mixture used to
start a cold engine.
In the past, some three-way catalytic converter systems used an air-injection tube
between the first (NOx reduction) and second (HC and CO oxidation) stages of the
converter. This tube was part of asecondary air injection system. The injected air
provided oxygen for the oxidation reactions. An upstream air injection point was also
sometimes present to provide oxygen during engine warmup, which caused unburned
fuel to ignite in the exhaust tract before reaching the catalytic converter. This cleaned
up the exhaust and reduced the engine runtime needed for the catalytic converter to
reach its "light-off" or operating temperature.
Most modern catalytic converter systems do not have air injection systems.[citation
needed] Instead, they provide a constantly varying air-fuel mixture that quickly and
continually cycles between lean and rich exhaust. Oxygen sensors are used to
monitor the exhaust oxygen content before and after the catalytic converter and this
information is used by the Electronic control unit to adjust the fuel injection so as to
prevent the first (NOx reduction) catalyst from becoming oxygen-loaded while ensuring
the second (HC and CO oxidization) catalyst is sufficiently oxygen-saturated. The
reduction and oxidation catalysts are typically contained in a common housing,
however in some instances they may be housed separately.
Damage
Poisoning
Catalyst poisoning occurs when the catalytic converter is exposed to exhaust
containing substances that coat the working surfaces, encapsulating the catalyst so
that it cannot contact and treat the exhaust. The most-notable contaminant is lead, so
vehicles equipped with catalytic converters can be run only on unleaded gasoline.
Other common catalyst poisons include fuel sulfur, manganese(originating primarily
from the gasoline additive MMT), and silicone, which can enter the exhaust stream if
the engine has a leak, allowing coolant into the combustion chamber. Phosphorus is
another catalyst contaminant. Although phosphorus is no longer used in gasoline, it
(and zinc, another low-level catalyst contaminant) was until recently widely used in
engine oil antiwear additives such aszinc dithiophosphate (ZDDP). Beginning in 2006,
a rapid phaseout of ZDDP in engine oils began.[citation needed]
Depending on the contaminant, catalyst poisoning can sometimes be reversed by
running the engine under a very heavy load for an extended period of time. The
increased exhaust temperature can sometimes liquefy or sublime the contaminant,
removing it from the catalytic surface. However, removal of lead deposits in this
manner is usually not possible because of lead's high boiling point.
Meltdown
Any condition that causes abnormally high levels of unburned hydrocarbons — raw or
partially burnt fuel — to reach the converter will tend to significantly elevate its
temperature, bringing the risk of a meltdown of the substrate and resultant catalytic
deactivation and severe exhaust restriction. Vehicles equipped with OBD-II diagnostic
systems are designed to alert the driver to a misfire condition by means of flashing the
"check engine" light on the dashboard.
Emissions regulations vary considerably from jurisdiction to jurisdiction. The earliest
on-road regulations which forced the use of Catalytic converters were the California
For Non-Road regulations California led the way with its 2001 Large Spark Ignition
Engine Regulation. This was followed by the United States Environmental Protection
Agency 50 State Program forNon-Road spark-ignition engines of over 25 brake
horsepower (19 kW) output built after January 1, 2004, are equipped with three-way
catalytic converters. In Japan, a similar set of regulations came into effect January 1,
2007. The European Union has regulations[8] beginning with Euro 1 regulations in
1992 and becoming progressively more stringent in subsequent years.[9]
Most automobile spark-ignition engines in North America have been fitted with
catalytic converters since the mid-1970s, and the technology used in non-automotive
applications is generally based on automotive technology.
Regulations for diesel engines are similarly varied, with some jurisdictions focusing on
NOx (nitric oxide and nitrogen dioxide) emissions and others focusing on particulate
(soot) emissions. This regulatory diversity is challenging for manufacturers of engines,
as it may not be economical to design an engine to meet two sets of regulations.
Regulations of fuel quality vary across jurisdictions. In North America, Europe, Japan
and Hong Kong, gasoline and diesel fuel are highly regulated, and compressed
natural gas and LPG (Autogas) are being reviewed for regulation. In most of Asia and
Africa, the regulations are often lax — in some places sulfur content of the fuel can
reach 20,000 parts per million (2%). Any sulfur in the fuel can be oxidized to
SO2 (sulfur dioxide) or even SO3 (sulfur trioxide) in the combustion chamber. If sulfur
passes over a catalyst, it may be further oxidized in the catalyst, i.e., SO2 may be
further oxidized to SO3. Sulfur oxides are precursors to sulfuric acid, a major
component of acid rain. While it is possible to add substances such as vanadium to
the catalyst washcoat to combat sulfur-oxide formation, such addition will reduce the
effectiveness of the catalyst. The most effective solution is to further refine fuel at the
refinery to produce ultra-low sulfur diesel. Regulations in Japan, Europe and North
America tightly restrict the amount of sulfur permitted in motor fuels. However, the
expense of producing such clean fuel may make it impractical for use in developing
countries. As a result, cities in these countries with high levels of vehicular traffic
suffer from acid rain, which damages stone and woodwork of buildings, poisons
humans and other animals, and damages local ecosystems.
Negative aspects
Some early converter designs greatly restricted the flow of exhaust, which negatively
affected vehicle performance, driveability, and fuel economy.[10] Because they were
used with carburetors incapable of precise fuel-air mixture control, they could
overheat and set fire to flammable materials under the car.[11] Removing a modern
catalytic converter in new condition will not increase vehicle performance without
retuning,[12] but their removal or "gutting" continues.[10][13] The exhaust section where
the converter was may be replaced with a welded-in section of straight pipe, or a
flanged section of "test pipe" legal for off-road use that can then be replaced with a
similarly fitted converter-choked section for legal on-road use, or emissions testing.[12] In the U.S. and many other jurisdictions, it is illegal to remove or disable a catalytic
converter for any reason other than its immediate replacement[citation needed]. It is a
violation of Section 203(a)(3)(A) of the 1990 Clean Air Act for a vehicle owner to
remove a converter from their own vehicle. Section 203(a)(3)(B) makes it illegal for
any person to sell or to install any part where a principle effect would be to bypass,
defeat, or render inoperative any device or element of design of a vehicles emission
control system. Vehicles without functioning catalytic converters generally fail
emission inspections. The automotive aftermarket supplies high-flow converters for
vehicles with upgraded engines, or whose owners prefer an exhaust system with
larger-than-stock capacity.[14]
Warm-up period
Most of the pollution put out by a car occurs during the first five minutes before the
catalytic converter has warmed up sufficiently.[15]
In 1999, BMW introduced the Electric Catalytic Convert, or "E-CAT", in their
flagship E38 750iL sedan. Coils inside the catalytic converter assemblies are heated
electrically just after engine start, bringing the catalyst up to operating temperature
much faster than traditional catalytic converters can, providing cleaner cold starts
and low emission vehicle (LEV) compliance.[citation needed]
Environmental impact
Catalytic converters have proven to be reliable and effective in reducing noxious
tailpipe emissions. However, they may have some adverse environmental impacts in
use:
The requirement for an internal combustion engine equipped with a three-way
catalyst to run at the stoichiometric point means it is less efficient than if it were
operated lean. Thus, there is an increases the amount of fossil fuel consumed and
the carbon-dioxide emissions from the vehicle. However, NOx control on lean-burn
engines is problematic and requires special lean NOx catalysts to meet U.S.
emissions regulations.[citation needed]
Although catalytic converters are effective at removing hydrocarbons and other
harmful emissions, they do not solve the fundamental problem created by burning
a fossil fuel. In addition to water, the main combustion product in exhaust gas
leaving the engine — through a catalytic converter or not — is carbon dioxide
(CO2).[16] Carbon dioxide produced from fossil fuels is one of the greenhouse
gases indicated by the Intergovernmental Panel on Climate Change (IPCC) to be a
"most likely" cause of global warming.[17] Additionally, the U.S. EPA has stated
catalytic converters are a significant and growing cause of global warming,
because of their release of nitrous oxide (N2O), a greenhouse gas over three
hundred times more potent than carbon dioxide.[18]
Catalytic converter production requires palladium or platinum; part of the world
supply of these precious metals is produced near Norilsk, Russia, where the
industry (among others) has caused Norilsk to be added to Time magazine's list of
most-polluted places.[19]
Theft
Because of the external location and the use of valuable precious metals
including platinum, palladium, and rhodium, converters are a target for thieves. The
problem is especially common among late-model Toyota trucks and SUVs, because
of their high ground clearance and easily removed bolt-on catalytic converters.
Welded-in converters are also at risk of theft from SUVs and trucks, as they can be
easily removed.[20][21] Theft removal of the converter can often inadvertently damage
the car's wiring or fuel line resulting in dangerous consequences. Rises in metal costs
in the U.S. during recent years have led to a large increase in theft incidents of the
converter,[22] which can then cost well over $1,000 to replace.[23]
Diagnostics
Various jurisdictions now legislate on-board diagnostics to monitor the function and
condition of the emissions-control system, including the catalytic converter. On-board
diagnostic systems take several forms.
Temperature sensors
Temperature sensors are used for two purposes. The first is as a warning system,
typically on two-way catalytic converters such as are still sometimes used on LPG
forklifts. The function of the sensor is to warn of catalytic converter temperature above
the safe limit of 750 °C (1,380 °F). More-recent catalytic-converter designs are not as
susceptible to temperature damage and can withstand sustained temperatures of 900
°C (1,650 °F).[citation needed] Temperature sensors are also used to monitor catalyst
functioning — usually two sensors will be fitted, with one before the catalyst and one
after to monitor the temperature rise over the catalytic-converter core. For every 1% of
CO in the exhaust gas stream, the exhaust gas temperature will rise by 100 °C.[citation
needed]
Oxygen sensors
The oxygen sensor is the basis of the closed-loop control system on a spark-ignited
rich-burn engine; however, it is also used for diagnostics. In vehicles with OBD II, a
second oxygen sensor is fitted after the catalytic converter to monitor the O2 levels.
The on-board computer makes comparisons between the readings of the two sensors.
If both sensors show the same output, the computer recognizes that the catalytic
converter either is not functioning or has been removed, and will operate a "check
engine" light and retard engine performance. Simple "oxygen sensor simulators" have
been developed to circumvent this problem by simulating the change across the
catalytic converter with plans and pre-assembled devices available on the Internet.
Although these are not legal for on-road use, they have been used with mixed results.[24] Similar devices apply an offset to the sensor signals, allowing the engine to run a
more fuel-economical lean burn that may, however, damage the engine or the
catalytic converter.[25]
NOx sensors
NOx sensors are extremely expensive and are in general used only when a
compression-ignition engine is fitted with a selective catalytic-reduction (SCR)
converter, or a NOx absorber catalyst in a feedback system. When fitted to an SCR
system, there may be one or two sensors. When one sensor is fitted it will be pre-
catalyst; when two are fitted, the second one will be post-catalyst. They are used for
the same reasons and in the same manner as an oxygen sensor — the only
difference is the substance being monitored.
Electronic Engine Management
GM Powertrain has long been a pioneer in offering electronic engine management for
industrial engines,adapting the technology that has transformed the automotive
industry to the specific needs of the industrial environment. The "brain" in every GM
Powertrain engine management system is an Electronic Control Module (ECM) which
was developed specifically for the industrial engine market. The ECM takes input from
various sensors and then uses that data to continually optimize engine operation and
performance. For example, if the engine knock sensor indicates there is premature
detonation, the ECM instantly adjusts spark timing to eliminate the problem. In
industrial applications, this can greatly increase the service life of the engine
For maximum reliability, GM Powertrain's commercial ECMs are manufactured using
thick-film hybrid technology, a technology more advanced than what is used in much
of the automotive industry. The circuits are formed by printing layers of conductive
and nonconductive ink onto a ceramic substrate. The result is an extremely rugged
and durable module that can handle very high temperatures and severe vibrations.
This enables the OEM to mount the ECM directly onto the engine. It is one example
of GM Powertrain's dedication to meeting the specific needs of the industrial engine
market
UNIT 2 ENGINE AUXILIARY SYSTEMS
Carburetor
Principles
The carburetor works on Bernoulli's principle: the faster air moves, the lower its static
pressure, and the higher its dynamic pressure. The throttle (accelerator) linkage does
not directly control the flow of liquid fuel. Instead, it actuates carburetor mechanisms
which meter the flow of air being pulled into the engine. The speed of this flow, and
therefore its pressure, determines the amount of fuel drawn into the airstream.
When carburetors are used in aircraft with piston engines, special designs and
features are needed to prevent fuel starvation during inverted flight. Later engines
used an early form of fuel injection known as a pressure carburetor.
Most production carbureted (as opposed to fuel-injected) engines have a single
carburetor and a matching intake manifold that divides and transports the air fuel
mixture to the intake valves, though some engines (like motorcycle engines) use
multiple carburetors on split heads. Multiple carburetor engines were also common
enhancements for modifying engines in the USA from the 1950s to mid-1960s, as well
as during the following decade of high-performance muscle cars fueling different
chambers of the engine's intake manifold.
Older engines used updraft carburetors, where the air enters from below the
carburetor and exits through the top. This had the advantage of never "flooding" the
engine, as any liquid fuel droplets would fall out of the carburetor instead of into
the intake manifold; it also lent itself to use of an oil bath air cleaner, where a pool of
oil below a mesh element below the carburetor is sucked up into the mesh and the air
is drawn through the oil-covered mesh; this was an effective system in a time when
paper air filters did not exist.
Beginning in the late 1930s, downdraft carburetors were the most popular type for
automotive use in the United States. In Europe, the sidedraft carburetors replaced
downdraft as free space in the engine bay decreased and the use of the SU-type
carburetor (and similar units from other manufacturers) increased. Some small
propeller-driven aircraft engines still use the updraft carburetor design.
Outboard motor carburetors are typically sidedraft, because they must be stacked one
on top of the other in order to feed the cylinders in a vertically oriented cylinder block.
1979 Evinrude Type I marine sidedraft carburetor
The main disadvantage of basing a carburetor's operation on Bernoulli's principle is
that, being a fluid dynamic device, the pressure reduction in a venturi tends to be
proportional to the square of the intake air speed. The fuel jets are much smaller and
limited mainly by viscosity, so that the fuel flow tends to be proportional to the
pressure difference. So jets sized for full power tend to starve the engine at lower
speed and part throttle. Most commonly this has been corrected by using multiple jets.
In SU and other movable jet carburetors, it was corrected by varying the jet size. For
cold starting, a different principle was used, in multi-jet carburetors. A flow resisting
valve called a choke, similar to the throttle valve, was placed upstream of the main jet
to reduce the intake pressure and suck additional fuel out of the jets.
[edit]Operation
Fixed-venturi, in which the varying air velocity in the venturi alters the fuel flow;
this architecture is employed in most carburetors found on cars.
Variable-venturi, in which the fuel jet opening is varied by the slide (which
simultaneously alters air flow). In "constant depression" carburetors, this is done by
a vacuum operated piston connected to a tapered needle which slides inside the
fuel jet. A simpler version exists, most commonly found on small motorcycles and
dirt bikes, where the slide and needle is directly controlled by the throttle position.
The most common variable venturi (constant depression) type carburetor is the
sidedraft SU carburetor and similar models from Hitachi, Zenith-Stromberg and
other makers. The UK location of the SU and Zenith-Stromberg companies helped
these carburetors rise to a position of domination in the UK car market, though
such carburetors were also very widely used on Volvos and other non-UK makes.
Other similar designs have been used on some European and a few Japanese
automobiles. These carburetors are also referred to as "constant velocity" or
"constant vacuum" carburetors. An interesting variation was Ford's VV (Variable
Venturi) carburetor, which was essentially a fixed venturi carburetor with one side
of the venturi hinged and movable to give a narrow throat at low rpm and a wider
throat at high rpm. This was designed to provide good mixing and airflow over a
range of engine speeds, though the VV carburetor proved problematic in service.
A high performance 4-barrel carburetor.
Under all engine operating conditions, the carburetor must:
Measure the airflow of the engine
Deliver the correct amount of fuel to keep the fuel/air mixture in the proper
range (adjusting for factors such as temperature)
Mix the two finely and evenly
This job would be simple if air and gasoline (petrol) were ideal fluids; in practice,
however, their deviations from ideal behavior due to viscosity, fluid drag, inertia, etc.
require a great deal of complexity to compensate for exceptionally high or low engine
speeds. A carburetor must provide the proper fuel/air mixture across a wide range of
ambient temperatures, atmospheric pressures, engine speeds and loads,
and centrifugal forces:
Cold start
Hot start
Idling or slow-running
Acceleration
High speed / high power at full throttle
Cruising at part throttle (light load)
In addition, modern carburetors are required to do this while maintaining low rates
of exhaust emissions.
To function correctly under all these conditions, most carburetors contain a complex
set of mechanisms to support several different operating modes, called circuits.
[edit]Basics
Cross-sectional schematic of a downdraft carburetor
A carburetor basically consists of an open pipe through which the air passes into
the inlet manifold of the engine. The pipe is in the form of a venturi: it narrows in
section and then widens again, causing the airflow to increase in speed in the
narrowest part. Below the venturi is a butterfly valve called the throttle valve — a
rotating disc that can be turned end-on to the airflow, so as to hardly restrict the flow
at all, or can be rotated so that it (almost) completely blocks the flow of air. This valve
controls the flow of air through the carburetor throat and thus the quantity of air/fuel
mixture the system will deliver, thereby regulating engine power and speed. The
throttle is connected, usually through a cable or a mechanical linkage of rods and
joints or rarely by pneumatic link, to the accelerator pedal on a car or the equivalent
control on other vehicles or equipment.
Fuel is introduced into the air stream through small holes at the narrowest part of the
venturi and at other places where pressure will be lowered when not running on full
throttle. Fuel flow is adjusted by means of precisely calibrated orifices, referred to
as jets, in the fuel path.
[edit]Off-idle circuit
As the throttle is opened up slightly from the fully closed position, the throttle plate
uncovers additional fuel delivery holes behind the throttle plate where there is a low
pressure area created by the throttle plate blocking air flow; these allow more fuel to
flow as well as compensating for the reduced vacuum that occurs when the throttle is
opened, thus smoothing the transition to metering fuel flow through the regular open
throttle circuit.
[edit]Main open-throttle circuit
As the throttle is progressively opened, the manifold vacuum is lessened since there
is less restriction on the airflow, reducing the flow through the idle and off-idle circuits.
This is where the venturishape of the carburetor throat comes into play, due
to Bernoulli's principle (i.e., as the velocity increases, pressure falls). The venturi
raises the air velocity, and this high speed and thus low pressure sucks fuel into the
airstream through a nozzle or nozzles located in the center of the venturi. Sometimes
one or more additional booster venturis are placed coaxially within the primary
venturi to increase the effect.
As the throttle is closed, the airflow through the venturi drops until the lowered
pressure is insufficient to maintain this fuel flow, and the idle circuit takes over again,
as described above.
Bernoulli's principle, which is a function of the velocity of the fluid, is a dominant effect
for large openings and large flow rates, but since fluid flow at small scales and low
speeds (low Reynolds number) is dominated by viscosity, Bernoulli's principle is
ineffective at idle or slow running and in the very small carburetors of the smallest
model engines. Small model engines have flow restrictions ahead of the jets to reduce
the pressure enough to suck the fuel into the air flow. Similarly the idle and slow
running jets of large carburetors are placed after the throttle valve where the pressure
is reduced partly by viscous drag, rather than by Bernoulli's principle. The most
common rich mixture device for starting cold engines was the choke, which works on
the same principle.
[edit]Power valve
For open throttle operation a richer mixture will produce more power, prevent pre-
ignition detonation, and keep the engine cooler. This is usually addressed with a
spring-loaded "power valve", which is held shut by engine vacuum. As the throttle
opens up, the vacuum decreases and the spring opens the valve to let more fuel into
the main circuit. On two-stroke engines, the operation of the power valve is the
reverse of normal — it is normally "on" and at a set rpm it is turned "off". It is activated
at high rpm to extend the engine's rev range, capitalizing on a two-stroke's tendency
to rev higher momentarily when the mixture is lean.
Alternative to employing a power valve, the carburetor may utilize a metering
rod or step-up rod system to enrich the fuel mixture under high-demand conditions.
Such systems were originated by Carter Carburetor[citation needed] in the 1950s for the
primary two venturis of their four barrel carburetors, and step-up rods were widely
used on most 1-, 2-, and 4-barrel Carter carburetors through the end of production in
the 1980s. The step-up rods are tapered at the bottom end, which extends into the
main metering jets. The tops of the rods are connected to a vacuum piston and/or a
mechanical linkage which lifts the rods out of the main jets when the throttle is opened
(mechanical linkage) and/or when manifold vacuum drops (vacuum piston). When the
step-up rod is lowered into the main jet, it restricts the fuel flow. When the step-up rod
is raised out of the jet, more fuel can flow through it. In this manner, the amount of fuel
delivered is tailored to the transient demands of the engine. Some 4-barrel
carburetors use metering rods only on the primary two venturis, but some use them
on both primary and secondary circuits, as in the Rochester Quadrajet.
[edit]Accelerator pump
Liquid gasoline, being denser than air, is slower than air to react to a force applied to
it. When the throttle is rapidly opened, airflow through the carburetor increases
immediately, faster than the fuel flow rate can increase. This transient oversupply of
air causes a lean mixture, which makes the engine misfire (or "stumble")—an effect
opposite what was demanded by opening the throttle. This is remedied by the use of a
small piston or diaphragm pump which, when actuated by the throttle linkage, forces a
small amount of gasoline through a jet into the carburetor throat.[4] This extra shot of
fuel counteracts the transient lean condition on throttle tip-in. Most accelerator pumps
are adjustable for volume and/or duration by some means. Eventually the seals
around the moving parts of the pump wear such that pump output is reduced; this
reduction of the accelerator pump shot causes stumbling under acceleration until the
seals on the pump are renewed.
The accelerator pump is also used to prime the engine with fuel prior to a cold start.
Excessive priming, like an improperly adjusted choke, can cause flooding. This is
when too much fuel and not enough air are present to support combustion. For this
reason, most carburetors are equipped with an unloader mechanism: The accelerator
is held at wide open throttle while the engine is cranked, the unloader holds the choke
open and admits extra air, and eventually the excess fuel is cleared out and the
engine starts.
[edit]Choke
When the engine is cold, fuel vaporizes less readily and tends to condense on the
walls of the intake manifold, starving the cylinders of fuel and making the engine
difficult to start; thus, a richer mixture (more fuel to air) is required to start and run
the engine until it warms up. A richer mixture is also easier to ignite.
To provide the extra fuel, a choke is typically used; this is a device that restricts the
flow of air at the entrance to the carburetor, before the venturi. With this restriction in
place, extra vacuum is developed in the carburetor barrel, which pulls extra fuel
through the main metering system to supplement the fuel being pulled from the idle
and off-idle circuits. This provides the rich mixture required to sustain operation at low
engine temperatures.
In addition, the choke can be connected to a cam (the fast idle cam) or other such
device which prevents the throttle plate from closing fully while the choke is in
operation. This causes the engine to idle at a higher speed. Fast idle serves as a way
to help the engine warm up quickly, and give a more stable idle while cold by
increasing airflow throughout the intake system which helps to better atomize the cold
fuel.
In many carbureted cars, the choke is controlled by a cable connected to a pull-knob
on the dashboard operated by the driver. In some carbureted cars it is automatically
controlled by a thermostatemploying a bimetallic spring, which is exposed to engine
heat, or to an electric heating element. This heat may be transferred to the choke
thermostat via simple convection, via engine coolant, or via air heated by the exhaust.
More recent designs use the engine heat only indirectly: A sensor detects engine heat
and varies electrical current to a small heating element, which acts upon the bimetallic
spring to control its tension, thereby controlling the choke. A choke unloader is a
linkage arrangement that forces the choke open against its spring when the vehicle's
accelerator is moved to the end of its travel. This provision allows a "flooded" engine
to be cleared out so that it will start.
Some carburetors do not have a choke but instead use a mixture enrichment circuit,
or enrichener. Typically used on small engines, notably motorcycles, enricheners
work by opening a secondary fuel circuit below the throttle valves. This circuit works
exactly like the idle circuit, and when engaged it simply supplies extra fuel when the
throttle is closed.
Classic British motorcycles, with side-draft slide throttle carburetors, used another
type of "cold start device", called a "tickler". This is simply a spring-loaded rod that,
when depressed, manually pushes the float down and allows excess fuel to fill the
float bowl and flood the intake tract. If the "tickler" is held down too long it also floods
the outside of the carburetor and the crankcase below, and is therefore a fire hazard.
[edit]Other elements
The interactions between each circuit may also be affected by various mechanical or
air pressure connections and also by temperature sensitive and electrical
components. These are introduced for reasons such as response, fuel
efficiency or automobile emissions control. Various air bleeds (often chosen from a
precisely calibrated range, similarly to the jets) allow air into various portions of the
fuel passages to enhance fuel delivery and vaporization. Extra refinements may be
included in the carburetor/manifold combination, such as some form of heating to aid
fuel vaporization such as anearly fuel evaporator.
[edit]Fuel supply
[edit]Float chamber
Holley "Visi-Flo" model #1904 carburetors from the 1950s, factory equipped with transparent glass
bowls.
To ensure a ready mixture, the carburetor has a "float chamber" (or "bowl") that
contains a quantity of fuel at near-atmospheric pressure, ready for use. This reservoir
is constantly replenished with fuel supplied by a fuel pump. The correct fuel level in
the bowl is maintained by means of a float controlling an inletvalve, in a manner very
similar to that employed in a cistern (e.g. a toilet tank). As fuel is used up, the float
drops, opening the inlet valve and admitting fuel. As the fuel level rises, the float rises
and closes the inlet valve. The level of fuel maintained in the float bowl can usually be
adjusted, whether by a setscrew or by something crude such as bending the arm to
which the float is connected. This is usually a critical adjustment, and the proper
adjustment is indicated by lines inscribed into a window on the float bowl, or a
measurement of how far the float hangs below the top of the carburetor when
disassembled, or similar. Floats can be made of different materials, such as
sheet brass soldered into a hollow shape, or of plastic; hollow floats can spring small
leaks and plastic floats can eventually become porous and lose their flotation; in either
case the float will fail to float, fuel level will be too high, and the engine will not run
unless the float is replaced. The valve itself becomes worn on its sides by its motion in
its "seat" and will eventually try to close at an angle, and thus fails to shut off the fuel
completely; again, this will cause excessive fuel flow and poor engine operation.
Conversely, as the fuel evaporates from the float bowl, it leaves sediment, residue,
and varnishes behind, which clog the passages and can interfere with the float
operation. This is particularly a problem in automobiles operated for only part of the
year and left to stand with full float chambers for months at a time; commercial fuel
stabilizer additives are available that reduce this problem.
Usually, special vent tubes allow air to escape from the chamber as it fills or enter as
it empties, maintaining atmospheric pressure within the float chamber; these usually
extend into the carburetor throat. Placement of these vent tubes can be somewhat
critical to prevent fuel from sloshing out of them into the carburetor, and sometimes
they are modified with longer tubing. Note that this leaves the fuel at atmospheric
pressure, and therefore it cannot travel into a throat which has been pressurized by
a supercharger mounted upstream; in such cases, the entire carburetor must be
contained in an airtight pressurized box to operate. This is not necessary in
installations where the carburetor is mounted upstream of the supercharger, which is
for this reason the more frequent system. However, this results in the supercharger
being filled with compressed fuel/air mixture, with a strong tendency to explode should
the engine backfire; this type of explosion is frequently seen in drag races, which for
safety reasons now incorporate pressure releasing blow-off plates on the intake
manifold, breakaway bolts holding the supercharger to the manifold, and shrapnel-
catching ballistic nylon blankets surrounding the superchargers.
If the engine must be operated in any orientation (for example a chain saw), a float
chamber cannot work. Instead, a diaphragm chamber is used. A flexible diaphragm
forms one side of the fuel chamber and is arranged so that as fuel is drawn out into
the engine the diaphragm is forced inward by ambient air pressure. The diaphragm is
connected to the needle valve and as it moves inward it opens the needle valve to
admit more fuel, thus replenishing the fuel as it is consumed. As fuel is replenished
the diaphragm moves out due to fuel pressure and a small spring, closing the needle
valve. A balanced state is reached which creates a steady fuel reservoir level, which
remains constant in any orientation.
[edit]Multiple carburetor barrels
Holley model #2280 2-barrel carburetor
Colombo Type 125 "Testa Rossa" engine in a 1961 Ferrari 250TR Spider with six Weber two-barrel
carburetors inducting air through 12 air horns; one individually adjustable barrel for each cylinder.
While basic carburetors have only one venturi, many carburetors have more than one
venturi, or "barrel". Two barrel and four barrel configurations are commonly used to
accommodate the higher air flow rate with large engine displacement. Multi-barrel
carburetors can have non-identical primary and secondary barrel(s) of different sizes
and calibrated to deliver different air/fuel mixtures; they can be actuated by the linkage
or by engine vacuum in "progressive" fashion, so that the secondary barrels do not
begin to open until the primaries are almost completely open. This is a desirable
characteristic which maximizes airflow through the primary barrel(s) at most engine
speeds, thereby maximizing the pressure "signal" from the venturis, but reduces the
restriction in airflow at high speeds by adding cross-sectional area for greater airflow.
These advantages may not be important in high-performance applications where part
throttle operation is irrelevant, and the primaries and secondaries may all open at
once, for simplicity and reliability; also, V-configuration engines, with two cylinder
banks fed by a single carburetor, may be configured with two identical barrels, each
supplying one cylinder bank. In the widely seen V8 and 4-barrel carburetor
combination, there are often two primary and two secondary barrels.
The spread-bore 4-barrel carburetor, first released by Rochester in the 1965 model
year as the "Quadrajet"[citation needed] has a much greater spreadbetween the sizes of the
primary and secondary throttle bores. The primaries in such a carburetor are quite
small relative to conventional 4-barrel practice, while the secondaries are quite large.
The small primaries aid low-speed fuel economy and drivability, while the large
secondaries permit maximum performance when it is called for. To tailor airflow
through the secondary venturis, each of the secondary throats has an air valve at the
top. This is configured much like a choke plate, and is lightly spring-loaded into the
closed position. The air valve opens progressively in response to engine speed and
throttle opening, gradually allowing more air to flow through the secondary side of the
carburetor. Typically, the air valve is linked to metering rods which are raised as the
air valve opens, thereby adjusting secondary fuel flow.
Multiple carburetors can be mounted on a single engine, often with progressive
linkages; two four-barrel carburetors (often referred to as "dual-quads") were
frequently seen on high performance American V8s, and multiple two barrel
carburetors are often now seen on very high performance engines. Large numbers of
small carburetors have also been used (see photo), though this configuration can limit
the maximum air flow through the engine due to the lack of a common plenum; with
individual intake tracts, not all cylinders are drawing air at once as the engine's
crankshaft rotates.[5]
[edit]Carburetor adjustment
Too much fuel in the fuel-air mixture is referred to as too rich, and not enough fuel is
too lean. The mixture is normally adjusted by one or more needle valveson an
automotive carburetor, or a pilot-operated lever on piston-engined aircraft (since
mixture is air density (altitude) dependent). The (stoichiometric) air togasoline ratio is
14.7:1, meaning that for each weight unit of gasoline, 14.7 units of air will be
consumed. Stoichiometric mixture are different for various fuels other than gasoline.
Ways to check carburetor mixture adjustment include: measuring the carbon
monoxide, hydrocarbon, and oxygen content of the exhaust using a gas analyzer, or
directly viewing the colour of the flame in the combustion chamber through a special
glass-bodied spark plug sold under the name "Colortune"; the flame colour of
stoichiometric burning is described as a "bunsen blue", turning to yellow if the mixture
is rich and whitish-blue if too lean.
The mixture can also be judged by removing and scrutinizing the spark plugs. black,
dry, sooty plugs indicate a mixture too rich; white to light gray plugs indicate a lean
mixture. A proper mixture is indicated by brownish-gray plugs.
In the 1980s, many American-market vehicles used special "feedback" carburetors
that could change the base mixture in response to signals from an exhaust
gas oxygen sensor. These were mainly used because they were less expensive than
fuel injection systems; they worked well enough to meet 1980s emissions
requirements and were based on existing carburetor designs. Eventually, however,
falling hardware prices and tighter emissions standards caused fuel injection to
supplant carburetors in new-vehicle production.
Where multiple carburetors are used the mechanical linkage of their throttles must be
synchronized for smooth engine running.
In this tutorial we will be looking at the Electronic Fuel Injection system, with particular focus upon the sensors and actuators, and their inputs and outputs to and from the vehicle's ECM. The tutorial looks at the multi-point injection system, with single-point being covered in a later tutorial.
Overview
Both the multi-point and the single-point systems operate in a very similar fashion, having an electromechanically operated injector or injectors opening for a predetermined length of time called the injector pulse width. The pulse width is determined by the engine’s Electronic Control Module (ECM and depends on the engine temperature, the engine load and the information from the oxygen (lambda) sensor. The fuel is delivered from the tank through a filter, and a regulator determines its operating pressure. The fuel is delivered to the engine in precise quantities and in most cases is injected into the inlet manifold to await the valve’s opening, then drawn into the combustion chamber by the incoming air.
The Fuel Tank
This is the obvious place to start in any full system explanation. Unlike the tanks on early carburettor-equipped vehicles, it is a sealed unit that allows the natural gassing of the fuel to aid delivery to the pump by slightly pressurising the system. When the filler cap is removed, pressure is heard to escape because the fuel filler caps are no longer vented.
The Fuel Pump
This type of high-pressure fuel pump (Fig 1.0) is called a roller cell pump, with the fuel entering the pump and being compressed by rotating cells which force it through the pump at a high pressure. The pump can produce a pressure of 8 bar (120 psi) with a delivery rate of approximately 4 to 5 litres per minute. Within the pump is a pressure relief valve that lifts off its seat at 8 bar to arrest the pressure if a blockage in the filter or fuel lines or elsewhere causes it to become obstructed. The other end of the pump (output) is home to a non-return valve which, when the voltage to the pump is removed, closes the return to the tank and maintains pressure within the system. The normal operating pressure within this system is approximately 2 bar (30 psi), at which the current draw on the pump is 3 to 5 amps. Fuel passing across the fuel pump's armature is subjected to sparks and arcing; this sounds quite dangerous, but the absence of oxygen means that there will not be an explosion!
Figure 1.0
The majority of fuel pumps fitted to today’s motor vehicles are fitted within the vehicle’s petrol tank and are referred to as ‘submerged’ fuel pumps. The pump is invariably be located with the fuel sender unit and both units can sometimes be accessed through an inspection hole either in the boot floor or under the rear seat. Mounted vertically, the pump comprises an inner and outer gear assembly that is called the ‘gerotor’. The combined assembly is secured in the tank using screws and sealed with a rubber gasket, or a bayonet-type locking ring. On some models, there are two fuel pumps, the submerged pump acting as a ‘lift’ pump to the external roller cell pump.
Figure 1.1
Figure 1.2
The waveform illustrated in Fig 1.1 shows the current for each sector of the commutator. The majority of fuel pumps have 6 to 8 sectors, and a repetitive point on the waveform can indicate wear and an impending failure. In the illustration waveform it can be seen that there is a lower current draw on one sector and this is repeated when the pump has rotated through 720°. This example has 8 sectors per rotation.
Fig 1.2 shows typical access to the fuel-submerged pump to measure current draw.
The current drawn by the fuel pump depends upon the fuel pressure but should be no more than 8 amps, as found on the Bosch K-Jetronic mechanical fuel injection which has a system pressure of 75 psi.
Fuel Supply
A conventional ‘flow and return’ system has a supply of fuel delivered to the fuel rail, and the unwanted fuel is passed through the pressure regulator back to the tank. It is the restriction in the fuel line created by the pressure regulator that provides the system operational pressure.
Returnless Fuel Systems
Have been adopted by several motor manufacturers and differ from the conventional by having a delivery pipe only to the fuel rail with no return flow back to the tank.
The returnless systems, both the mechanical and the electronic versions, were necessitated by emissions laws. The absence of heated petrol returning to the fuel tank reduces the amount of evaporative emissions, while the fuel lines are kept short, thus reducing build costs.
Mechanical Returnless Fuel Systems
The ‘returnless’ system differs from the norm by having the pressure regulator inside the fuel tank. When the fuel pump is activated, fuel flows into the system until the required pressure is obtained; at this point ‘excess’ fuel is bled past the pressure regulator and back into the tank.
The ‘flow and return’ system has a vacuum supply to the pressure regulator: this enables the fuel pressure to be increased whenever the manifold vacuum drops, providing fuel enrichment under acceleration.
The ‘returnless’ system has no mechanical compensation affecting the fuel pressure, which remains at a higher than usual 44 to 50 psi. By increasing the delivery pressure, the ECM (Electronic Control Module) can alter the injection pulse width to give the precise delivery, regardless of the engine load and without fuel pressure compensation.
Electronic Returnless Fuel Systems
This version has all the required components fitted within the one unit of the submersible fuel pump. It contains a small particle filter (in addition to the strainer), pump, electronic pressure regulator, fuel level sensor and a sound isolation system. The electronic pressure regulator allows the pressure to be increased under acceleration conditions, and the pump’s output can be adjusted to suit the engine's fuel demand. This prolongs the pump’s life as it is no longer providing a larger than required output delivery.
The Electronic Control Module (ECM) supplies the required pressure information, while the fuel pump’s output signal is supplied in the form of a digital squarewave. Altering the squarewave’s duty cycle affects the pump’s delivery output.
To compensate for the changing viscosity of the fuel with changing fuel temperature, a fuel rail temperature sensor is installed. A pulsation damper may also be fitted ahead of or inside the fuel rail.
Injectors
The injector is an electromechanical device, which is fed by a 12 volt supply from either the fuel injection relay or the ECM. The voltage is present only when the engine is cranking or running, because it is controlled by a tachometric relay. The injector is supplied with fuel from a common fuel rail. The injector pulse width depends on the input signals seen by the ECM from its various engine sensors, and varies to compensate for cold engine starting and warm-up periods, the initial wide pulse getting narrower as the engine warms to operating temperature. The pulse width also expands under acceleration and contracts under light load conditions.
The injector has constant voltage supply while the engine is running and the earth path is switched via the ECM. An example of a typical waveform is shown below in Fig 1.3.
Figure 1.3
Multi-point injection may be either sequential or simultaneous. A simultaneous system fires all 4 injectors at the same time with each cylinder receiving 2 injection pulses per cycle (720° crankshaft rotation). A sequential system receives just 1 injection pulse per cycle, timed to coincide with the opening of the inlet valve. As a very rough guide the injector pulse widths for an engine at normal operating temperature at idle speed are around 2.5 ms for simultaneous and 3.5 ms for sequential.
An electromechanical injector of course takes a short time to react, as it requires a level of magnetism to build before the pintle is lifted off its seat. This time is called the ‘solenoid reaction time’. This delay is important to monitor and can sometimes occupy a third of the total pulse width. A good example of the delay in opening can be seen in the example waveform shown below in Fig 1.4.
The waveform is ‘split’ into two clearly defined areas. The first part of the waveform is responsible for the electromagnetic force lifting the pintle, in this example taking approximately 0.6 ms. At this point the current can be seen to level off before rising again as the pintle is held open. With this level off ind it can be seen that the amount of time that the injector is held open is not necessarily the same as the time measured. It is not however possible to calculate the time taken for the injector’s spring to fully close the injector and cut off the fuel flow.
This test is ideal for identifying an injector with an unacceptably slow solenoid reaction time. Such an injector would not deliver the required amount of fuel and the cylinder in question would run lean.
Figure 1.4
Fig 1.5 shows both the injector voltage and current displayed simultaneously.
Figure 1.5
Fuel injection
Fuel rail connected to the injectors that are mounted just above the intake manifold on a four cylinder
engine.
Fuel injection is a system for admitting fuel into an internal combustion engine. It has become the primary fuel
delivery system used inautomotive petrol engines, having almost completely replaced carburetors in the late 1980s.
A fuel injection system is designed and calibrated specifically for the type(s) of fuel it will handle. Most fuel injection
systems are for gasoline ordiesel applications. With the advent of electronic fuel injection (EFI), the diesel and
gasoline hardware has become similar. EFI's programmablefirmware has permitted common hardware to be used
with different fuels.
Carburetors were the predominant method used to meter fuel on gasoline engines before the widespread use of fuel
injection. A variety of injection systems have existed since the earliest usage of the internal combustion engine.
The primary difference between carburetors and fuel injection is that fuel injection atomizes the fuel by forcibly
pumping it through a small nozzle under high pressure, while a carburetor relies on suction created by intake air
rushing through a venturi to draw the fuel into the airstream.
Objectives
The functional objectives for fuel injection systems can vary. All share the central task
of supplying fuel to the combustion process, but it is a design decision how a
particular system will be optimized. There are several competing objectives such as:
power output
fuel efficiency
emissions performance
ability to accommodate alternative fuels
reliability
driveability and smooth operation
initial cost
maintenance cost
diagnostic capability
range of environmental operation
Engine tuning
Certain combinations of these goals are conflicting, and it is impractical for a single
engine control system to fully optimize all criteria simultaneously. In practice,
automotive engineers strive to best satisfy a customer's needs competitively. The
modern digital electronic fuel injection system is far more capable at optimizing these
competing objectives consistently than a carburetor. Carburetors have the potential to
atomize fuel better (see Pogue and Allen Caggiano patents).
Benefits
Engine operation
Operational benefits to the driver of a fuel-injected car include smoother and more
dependable engine response during quick throttle transitions, easier and more
dependable engine starting, better operation at extremely high or low ambient
temperatures, increased maintenance intervals, and increased fuel efficiency. On a
more basic level, fuel injection does away with the choke which on carburetor-
equipped vehicles must be operated when starting the engine from cold and then
adjusted as the engine warms up.
An engine's air/fuel ratio must be precisely controlled under all operating conditions to
achieve the desired engine performance, emissions, driveability, and fuel economy.
Modern electronic fuel-injection systems meter fuel very accurately, and use closed
loop fuel-injection quantity-control based on a variety of feedback signals from
an oxygen sensor, a mass airflow (MAF) or manifold absolute pressure (MAP) sensor,
a throttle position (TPS), and at least one sensor on the crankshaft and/or camshaft(s)
to monitor the engine's rotational position. Fuel injection systems can react rapidly to
changing inputs such as sudden throttle movements, and control the amount of fuel
injected to match the engine's dynamic needs across a wide range of operating
conditions such as engine load, ambient air temperature, engine temperature, fuel
octane level, and atmospheric pressure.
A multipoint fuel injection system generally delivers a more accurate and equal mass
of fuel to each cylinder than can a carburetor, thus improving the cylinder-to-cylinder
distribution. Exhaustemissions are cleaner because the more precise and accurate
fuel metering reduces the concentration of toxic combustion byproducts leaving the
engine, and because exhaust cleanup devices such as the catalytic converter can be
optimized to operate more efficiently since the exhaust is of consistent and predictable
composition.
Fuel injection generally increases engine fuel efficiency. With the improved cylinder-
to-cylinder fuel distribution, less fuel is needed for the same power output. When
cylinder-to-cylinder distribution is less than ideal, as is always the case to some
degree with a carburetor or throttle body fuel injection, some cylinders receive excess
fuel as a side effect of ensuring that all cylinders receive sufficientfuel. Power output is
asymmetrical with respect to air/fuel ratio; burning extra fuel in the rich cylinders does
not reduce power nearly as quickly as burning too little fuel in the lean cylinders.
However, rich-running cylinders are undesirable from the standpoint of exhaust
emissions, fuel efficiency, engine wear, and engine oil contamination. Deviations from
perfect air/fuel distribution, however subtle, affect the emissions, by not letting the
combustion events be at the chemically ideal (stoichiometric) air/fuel ratio. Grosser
distribution problems eventually begin to reduce efficiency, and the grossest
distribution issues finally affect power. Increasingly poorer air/fuel distribution affects
emissions, efficiency, and power, in that order. By optimizing the homogeneity of
cylinder-to-cylinder mixture distribution, all the cylinders approach their maximum
power potential and the engine's overall power output improves.
A fuel-injected engine often produces more power than an equivalent carbureted
engine. Fuel injection alone does not necessarily increase an engine's maximum
potential output. Increased airflow is needed to burn more fuel, which in turn releases
more energy and produces more power. The combustion process converts the fuel's
chemical energy into heat energy, whether the fuel is supplied by fuel injectors or a
carburetor. However, airflow is often improved with fuel injection, the components of
which allow more design freedom to improve the air's path into the engine. In contrast,
a carburetor's mounting options are limited because it is larger, it must be carefully
oriented with respect to gravity, and it must be equidistant from each of the engine's
cylinders to the maximum practicable degree. These design constraints generally
compromise airflow into the engine. Furthermore, a carburetor relies on a
restrictive venturi to create a local air pressure difference, which forces the fuel into
the air stream. The flow loss caused by the venturi, however, is small compared to
other flow losses in the induction system. In a well-designed carburetor induction
system, the venturi is not a significant airflow restriction.
Fuel is saved while the car is coasting because the car's movement is helping to keep
the engine rotating, so less fuel is used for this purpose. Control units on modern cars
react to this and reduce or stop fuel flow to the engine reducing wear on the
brakes[citation needed].
History and development
Herbert Akroyd Stuart developed the first system laid out on modern lines (with a
highly accurate 'jerk pump' to meter out fuel oil at high pressure to an injector. This
system was used on the hot bulb engine and was adapted and improved by Robert
Bosch and Clessie Cummins for use on diesel engines — Rudolf Diesel's original
system employed a cumbersome[citation needed] 'air-blast' system using highly compressed
air[clarification needed].
The first use of direct gasoline injection was on the Hesselman engine invented by
Swedish engineer Jonas Hesselman in 1925.[1][2] Hesselman engines use the
ultra lean burn principle; fuel is injected toward the end of the compression stroke,
then ignited with a spark plug. They are often started on gasoline and then switched to
diesel or kerosene.[3] Fuel injection was in widespread commercial use in diesel
engines by the mid-1920s. Because of its greater immunity to wildly changing g-
forces on the engine, the concept was adapted for use in gasoline-powered aircraft
during World War II, and direct injection was employed in some notable designs like
the Junkers Jumo 210, the Daimler-Benz DB 601, the BMW 801, the Shvetsov ASh-
82FN (M-82FN) and later versions of the Wright R-3350used in the B-29
Superfortress.
Alfa Romeo tested one of the very first electric injection systems (Caproni-Fuscaldo)
in Alfa Romeo 6C2500 with "Ala spessa" body in 1940 Mille Miglia. The engine had
six electrically operated injectors and were fed by a semi-high pressure circulating fuel
pump system.[4]
Mechanical
The term Mechanical when applied to fuel injection is used to indicate that metering
functions of the fuel injection (how the correct amount of fuel for any given situation is
determined and delivered) is not achieved electronically but rather through
mechanical means alone.
In the 1940s, hot rodder Stuart Hilborn offered mechanical injection for
racers, salt cars, and midgets.[5]
One of the first commercial gasoline injection systems was a mechanical system
developed by Bosch and introduced in 1952 on the Goliath GP700 and Gutbrod
Superior 600. This was basically a high pressure diesel direct-injection pump with an
intake throttle valve set up. (Diesels only change amount of fuel injected to vary
output; there is no throttle.) This system used a normal gasoline fuel pump, to provide
fuel to a mechanically driven injection pump, which had separate plungers per injector
to deliver a very high injection pressure directly into the combustion chamber.
Another mechanical system, also by Bosch, but injecting the fuel into the port above
the intake valve was later used by Porsche from 1969 until 1973 for the 911
production range and until 1975 on the Carrera 3.0 in Europe. Porsche continued
using it on its racing cars into the late seventies and early eighties. Porsche racing
variants such as the 911 RSR 2.7 & 3.0, 904/6, 906, 907, 908, 910, 917 (in its regular
normally aspirated or 5.5 Liter/1500 HP Turbocharged form), and 935 all
used Bosch or Kugelfischer built variants of injection. The Kugelfischer system was
also used by the BMW 2000/2002 Tii and some versions of the Peugeot 404/504 and
Lancia Flavia. Lucas also offered a mechanical system which was used by some
Maserati, Aston Martin and Triumph models between ca. 1963 and 1973.
A system similar to the Bosch inline mechanical pump was built by SPICA for Alfa
Romeo, used on the Alfa Romeo Montreal and on US market 1750 and 2000 models
from 1969 to 1981. This was specifically designed to meet the US emission
requirements, and allowed Alfa to meet these requirements with no loss in
performance and a reduction in fuel consumption.
Chevrolet introduced a mechanical fuel injection option, made by General
Motors' Rochester Products division, for its 283 V8 engine in 1956 (1957 US model
year). This system directed the inducted engine air across a "spoon shaped" plunger
that moved in proportion to the air volume. The plunger connected to the fuel metering
system which mechanically dispensed fuel to the cylinders via distribution tubes. This
system was not a "pulse" or intermittent injection, but rather a constant flow system,
metering fuel to all cylinders simultaneously from a central "spider" of injection lines.
The fuel meter adjusted the amount of flow according to engine speed and load, and
included a fuel reservoir, which was similar to a carburetor's float chamber. With its
own high-pressure fuel pump driven by a cable from the distributor to the fuel meter,
the system supplied the necessary pressure for injection. This was "port" injection,
however, in which the injectors are located in the intake manifold, very near the intake
valve. (Direct fuel injection is a fairly recent innovation for automobile engines. As
recent as 1954 in the aforementioned Mercedes-Benz 300SL or the Gutbrod in 1953.)
The highest performance version of the fuel injected engine was rated at 283 bhp
(211.0 kW) from 283 cubic inches (4.6 L). This made it among the early production
engines in history to exceed 1 hp/in³ (45.5 kW/L), after Chrysler's Hemi engine and a
number of others. General Motors' fuel injected engine — usually referred to as the
"fuelie" — was optional on the Corvette for the 1957 model year.
During the 1960s, other mechanical injection systems such as Hilborn were
occasionally used on modified American V8 engines in various racing applications
such as drag racing, oval racing, and road racing.[6] These racing-derived systems
were not suitable for everyday street use, having no provisions for low speed metering
or often none even for starting (fuel had to be squirted into the injector tubes while
cranking the engine in order to start it). However they were a favorite in the
aforementioned competition trials in which essentially wide-open throttle operation
was prevalent. Constant-flow injection systems continue to be used at the highest
levels of drag racing, where full-throttle, high-RPM performance is key.[7]
Electronic
The first commercial electronic fuel injection (EFI) system was Electrojector,
developed by the Bendix Corporation and was to be offered by American
Motors (AMC) in 1957.[8][9] A special muscle carmodel, the Rambler Rebel, showcased
AMC's new 327 cu in (5.4 L) engine . The Electrojector was an option and rated at
288 bhp (214.8 kW).[10] With no Venturi effect or heated carburetor (to help vaporize
the gasoline) AMC's EFI equipped engine breathed easier with denser cold air to pack
more power sooner, reaching peak torque at 500 rpm lower than the equivalent no-
fuel injection engine.[6]The Rebel Owners Manual described the design and operation
of the new system.[11] Initial press information about the Bendix system in December
1956 was followed in March 1957 by a price bulletin that pegged the option
at US$395, but due to supplier difficulties, fuel-injected Rebels would only be available
after June 15.[12] This was to have been the first production EFI engine, but
Electrojector's teething problems meant only pre-production cars were so equipped:
thus, very few cars so equipped were ever sold[13] and none were made available to
the public.[14] The EFI system in the Rambler was a far more-advanced setup than the
mechanical types then appearing on the market and the engines ran fine in warm
weather, but suffered hard starting in cooler temperatures.[12]
Chrysler offered Electrojector on the 1958 Chrysler 300D, Dodge D500, Plymouth
Fury, and DeSoto Adventurer, arguably the first series-production cars equipped with
an EFI system. It was jointly engineered by Chrysler and Bendix. The early electronic
components were not equal to the rigors of underhood service, however, and were too
slow to keep up with the demands of "on the fly" engine control. Most of the 35
vehicles originally so equipped were field-retrofitted with 4-barrel carburetors. The
Electrojector patents were subsequently sold to Bosch.
Bosch developed an electronic fuel injection system, called D-Jetronic (D for Druck,
German for "pressure"), which was first used on the VW 1600TL/E in 1967. This was
a speed/density system, using engine speed and intake manifold air density to
calculate "air mass" flow rate and thus fuel requirements. This system was adopted
by VW, Mercedes-Benz, Porsche, Citroën, Saab, and Volvo. Lucas licensed the
system for production with Jaguar. Bosch superseded the D-Jetronic system with
the K-Jetronic and L-Jetronic systems for 1974, though some cars (such as the Volvo
164) continued using D-Jetronic for the following several years.
Chevrolet Cosworth Vega engine showing Bendix electronic fuel injection
The Cadillac Seville was introduced in 1975 with an EFI system made by Bendix and
modelled very closely on Bosch's D-Jetronic. L-Jetronic first appeared on the 1974
Porsche 914, and uses a mechanical airflow meter (L for Luft, German for "air") that
produces a signal that is proportional to "air volume". This approach required
additional sensors to measure the atmospheric pressure and temperature, to
ultimately calculate "air mass". L-Jetronic was widely adopted on European cars of
that period, and a few Japanese models a short time later.
The limited production Chevrolet Cosworth Vega was introduced in March 1975 using
a Bendix EFI system with pulse-time manifold injection, four injector valves, an
electronic control unit (ECU), five independent sensors and two fuel pumps. The EFI
system was developed to satisfy stringent emission control requirements and market
demands for a technologically advanced responsive vehicle. 5000 hand-built
Cosworth Vega engines were produced but only 3508 cars were sold through 1976.[15]
A major milestone was reached in 1980 when Motorola Corporation introduced the
first engine computer with microprocessor (digital) control, the EEC III module, which
is now the standard approach. The advent of the digital microprocessor permitted the
integration of all powertrain sub-systems into a single control module. [16]
In 1981 Chrysler Corporation introduced an EFI system featuring a sensor that directly
measures the air mass flow into the engine, on the Imperial automobile (5.2L V8) as
standard equipment. The mass air sensor utilizes a heated platinum wire placed in the
incoming air flow. The rate of the wire's cooling is proportional to the air mass flowing
across the wire. Since the hot wire sensor directly measures air mass, the need for
additional temperature and pressure sensors was eliminated. This system was
independently developed and engineered in Highland Park, Michigan and
manufactured at Chrysler's Electronics division in Huntsville, Alabama, USA.[17][18]
Supersession of carburetors
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When efficient combustion takes place in an internal combustion engine, the proper
number of fuel molecules and oxygen molecules are sent to the engine's combustion
chamber(s), where fuel combustion (i.e., fuel oxidation) takes place. When efficient
combustion takes place, neither extra fuel or extra oxygen molecules remain: each
fuel molecule is matched with the appropriate number of oxygen molecules. This
balanced condition is called stoichiometry.
In the 1970s and 1980s in the US, the federal government imposed increasingly
strict exhaust emission regulations. During that time period, the vast majority of
gasoline-fueled automobile and light truck engines did not use fuel injection. To
comply with the new regulations, automobile manufacturers often made extensive and
complex modifications to the engine carburetor(s). While a simple carburetor system
has certain advantages compared to the fuel injection systems that were available
during the 1970s and 1980s (including lower manufacturing cost), the more complex
carburetor systems installed on many engines beginning in the early 1970s did not
usually have these advantages. So in order to more easily comply with government
emissions control regulations, automobile manufacturers, beginning in the late 1970s,
furnished more of their gasoline-fueled engines with fuel injection systems, and fewer
with complex carburetor systems.
There are three primary types of toxic emissions from an internal combustion
engine: Carbon Monoxide (CO), unburnt hydrocarbons (HC), and oxides of
nitrogen (NOx). CO and HC result from incomplete combustion of fuel due to
insufficient oxygen in the combustion chamber. NOx, in contrast, results from
excessive oxygen in the combustion chamber. The opposite causes of these
pollutants makes it difficult to control all three simultaneously. Once the permissible
emission levels dropped below a certain point, catalytic treatment of these three main
pollutants became necessary. This required a particularly large increase in fuel
metering accuracy and precision, for simultaneous catalysis of all three pollutants
requires that the fuel/air mixture be held within a very narrow range of stoichiometry.
The open loop fuel injection systems had already improved cylinder-to-cylinder fuel
distribution and engine operation over a wide temperature range, but did not offer
sufficient fuel/air mixture control to enable effective exhaust catalysis. Closed
loop fuel injection systems improved the air/fuel mixture control with an exhaust
gas oxygen sensor. The O2 sensor is mounted in the exhaust system upstream of the
catalytic converter, and enables the engine management computer to determine and
adjust the air/fuel ratio precisely and quickly.
Fuel injection was phased in through the latter '70s and '80s at an accelerating rate,
with the US, French and German markets leading and the UK and Commonwealth
markets lagging somewhat, and since the early 1990s, almost all gasoline passenger
cars sold in first world markets like the United States, Canada, Europe, Japan, and
Australia have come equipped with electronic fuel injection (EFI). Many motorcycles
still utilize carbureted engines, though all current high-performance designs have
switched to EFI.
Fuel injection systems have evolved significantly since the mid-1980s. Current
systems provide an accurate, reliable and cost-effective method of metering fuel and
providing maximum engine efficiency with clean exhaust emissions, which is why EFI
systems have replaced carburetors in the marketplace. EFI is becoming more reliable
and less expensive through widespread usage. At the same time, carburetors are
becoming less available, and more expensive. Even marine applications are adopting
EFI as reliability improves. Virtually all internal combustion engines, including
motorcycles, off-road vehicles, and outdoor power equipment, may eventually use
some form of fuel injection.
The carburetor remains in use in developing countries where vehicle emissions are
unregulated and diagnostic and repair infrastructure is sparse. Fuel injection is
gradually replacing carburetors in these nations too as they adopt emission
regulations conceptually similar to those in force in Europe, Japan, Australia and
North America. NASCAR will legalize and adopt fuel injectors to take the place of
carburetors starting at the 2012 NASCAR Sprint Cup Series season.[19][20][21]
Basic function
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The process of determining the necessary amount of fuel, and its delivery into the
engine, are known as fuel metering. Early injection systems used mechanical
methods to meter fuel (non electronic, or mechanical fuel injection). Modern systems
are nearly all electronic, and use an electronic solenoid (the injector) to inject the fuel.
An electronic engine control unit calculates the mass of fuel to inject.
Modern fuel injection schemes follow much the same setup. There is a mass airflow
sensor or manifold absolute pressure sensor at the intake, typically mounted either in
the air tube feeding from the air filter box to the throttle body, or mounted directly to
the throttle body itself. The mass airflow sensor does exactly what its name implies; it
senses the mass of the air that flows past it, giving the computer an accurate idea of
how much air is entering the engine. The next component in line is the Throttle Body.
The throttle body has a throttle position sensor mounted onto it, typically on the
butterfly valve of the throttle body. The throttle position sensor (TPS) reports to the
computer the position of the throttle butterfly valve, which the ECM uses to calculate
the load upon the engine. The fuel system consists of a fuel pump (typically mounted
in-tank), a fuel pressure regulator, fuel lines (composed of either high strength plastic,
metal, or reinforced rubber), a fuel rail that the injectors connect to, and the fuel
injector(s). There is a coolant temperature sensor that reports the engine temperature
to the ECM, which the engine uses to calculate the proper fuel ratio required. In
sequential fuel injection systems there is a camshaft position sensor, which the ECM
uses to determine which fuel injector to fire. The last component is the oxygen sensor.
After the vehicle has warmed up, it uses the signal from the oxygen sensor to perform
fine tuning of the fuel trim.
The fuel injector acts as the fuel-dispensing nozzle. It injects liquid fuel directly into the
engine's air stream. In almost all cases this requires an external pump. The pump and
injector are only two of several components in a complete fuel injection system.
In contrast to an EFI system, a carburetor directs the induction air through a venturi,
which generates a minute difference in air pressure. The minute air pressure
differences both emulsify (premix fuel with air) the fuel, and then acts as the force to
push the mixture from the carburetor nozzle into the induction air stream. As more air
enters the engine, a greater pressure difference is generated, and more fuel is
metered into the engine. A carburetor is a self-contained fuel metering system, and is
cost competitive when compared to a complete EFI system.
An EFI system requires several peripheral components in addition to the injector(s), in
order to duplicate all the functions of a carburetor. A point worth noting during times of
fuel metering repair is that early EFI systems are prone to diagnostic ambiguity. A
single carburetor replacement can accomplish what might require numerous repair
attempts to identify which one of the several EFI system components is
malfunctioning. Newer EFI systems since the advent of OBD II diagnostic systems,
can be very easy to diagnose due to the increased ability to monitor the realtime data
streams from the individual sensors. This gives the diagnosing technician realtime
feedback as to the cause of the drivability concern, and can dramatically shorten the
number of diagnostic steps required to ascertain the cause of failure, something which
isn't as simple to do with a carburetor. On the other hand, EFI systems require little
regular maintenance; a carburetor typically requires seasonal and/or altitude
adjustments.
Detailed function
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Note: These examples specifically apply to a modern EFI gasoline engine. Parallels to fuels other than gasoline can be made, but only conceptually.
Typical EFI components
Animated cut through diagram of a typical fuel injector.
Injectors
Fuel Pump
Fuel Pressure Regulator
ECM - Engine Control Module; includes a digital computer and circuitry to
communicate with sensors and control outputs.
Wiring Harness
Various Sensors (Some of the sensors required are listed here.)
Crank/Cam Position: Hall effect sensor Airflow: MAF sensor, sometimes this is inferred with a MAP sensor Exhaust Gas Oxygen: Oxygen sensor, EGO sensor, UEGO sensor
Functional description
Central to an EFI system is a computer called the Engine Control Unit (ECU),
which monitors engine operating parameters via varioussensors. The ECU
interprets these parameters in order to calculate the appropriate amount of fuel to
be injected, among other tasks, and controls engine operation by manipulating fuel
and/or air flow as well as other variables. The optimum amount of injected fuel
depends on conditions such as engine and ambient temperatures, engine speed
and workload, and exhaust gas composition.
The electronic fuel injector is normally closed, and opens to inject pressurized fuel
as long as electricity is applied to the injector's solenoid coil. The duration of this
operation, called the pulse width, is proportional to the amount of fuel desired. The
electric pulse may be applied in closely controlled sequence with the valve events
on each individual cylinder (in a sequential fuel injection system), or in groups of
less than the total number of injectors (in a batch fire system).
Since the nature of fuel injection dispenses fuel in discrete amounts, and since the
nature of the 4-stroke engine has discrete induction (air-intake) events, the ECU
calculates fuel in discrete amounts. In a sequential system, the injected fuel mass
is tailored for each individual induction event. Every induction event, of every
cylinder, of the entire engine, is a separate fuel mass calculation, and each injector
receives a unique pulse width based on that cylinder's fuel requirements.
It is necessary to know the mass of air the engine "breathes" during each induction
event. This is proportional to the intake manifold's air pressure/temperature, which
is proportional to throttle position. The amount of air inducted in each intake event
is known as "air-charge", and this can be determined using several methods.
(See MAF sensor, and MAP sensor.)
The three elemental ingredients for combustion are fuel, air and ignition. However,
complete combustion can only occur if the air and fuel is present in the
exact stoichiometric ratio, which allows all the carbon and hydrogen from the fuel
to combine with all the oxygen in the air, with no undesirable polluting
leftovers. Oxygen sensors monitor the amount of oxygen in the exhaust, and the
ECU uses this information to adjust the air-to-fuel ratio in real-time.
To achieve stoichiometry, the air mass flow into the engine is measured and
multiplied by the stoichiometric air/fuel ratio 14.64:1 (by weight) for gasoline. The
required fuel mass that must be injected into the engine is then translated to the
required pulse width for the fuel injector. The stoichiometric ratio changes as a
function of the fuel; diesel, gasoline, ethanol, methanol, propane, methane (natural
gas), or hydrogen.
Deviations from stoichiometry are required during non-standard operating
conditions such as heavy load, or cold operation, in which case, the mixture ratio
can range from 10:1 to 18:1 (for gasoline). In early fuel injection systems this was
accomplished with a thermotime switch.
Pulse width is inversely related to pressure difference across the injector inlet and
outlet. For example, if the fuel line pressure increases (injector inlet), or the
manifold pressure decreases (injector outlet), a smaller pulse width will admit the
same fuel. Fuel injectors are available in various sizes and spray characteristics as
well. Compensation for these and many other factors are programmed into the
ECU's software.
Various injection schemes
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Single-point injection
Single-point injection, called Throttle-body injection (TBI) by General
Motors and Central Fuel Injection (CFI) by Ford, was introduced in the 1940s in
large aircraft engines (then called thepressure carburetor) and in the 1980s in the
automotive world. The SPI system injects fuel at the throttle body (the same location
where a carburetor introduced fuel). The induction mixture passes through the intake
runners like a carburetor system, and is thus labelled a "wet manifold system". Fuel
pressure is usually specified to be in the area of 10-15 psi. The justification for single-
point injection was low cost. Many of the carburetor's supporting components could be
reused such as the air cleaner, intake manifold, and fuel line routing. This postponed
the redesign and tooling costs of these components. Most of these components were
later redesigned for the next phase of fuel injection's evolution, which is individual port
injection, commonly known as MPFI or "multi-point fuel injection". TBI was used
extensively on American-made passenger cars and light trucks in the 1980-1995
timeframe and some transition-engined European cars throughout the early and mid-
1990s. Mazda called their system EGI, and even introduced an electronically
controlled version called the EGI-S.
Continuous injection
In a continuous injection system, fuel flows at all times from the fuel injectors, but at a
variable flow rate. This is in contrast to most fuel injection systems, which provide fuel
during short pulses of varying duration, with a constant rate of flow during each pulse.
Continuous injection systems can be multi-point or single-point, but not direct.
The most common automotive continuous injection system is Bosch's K-Jetronic (K
for kontinuierlich, German for "continuous" — a.k.a. CIS — Continuous Injection
System), introduced in 1974. Gasoline is pumped from the fuel tank to a large control
valve called a fuel distributor, which separates the single fuel supply pipe from the
tank into smaller pipes, one for each injector. The fuel distributor is mounted atop a
control vane through which all intake air must pass, and the system works by varying
fuel volume supplied to the injectors based on the angle of the air vane, which in turn
is determined by the volume flowrate of air past the vane, and by the control pressure.
The control pressure is regulated with a mechanical device called the control pressure
regulator (CPR) or the warm-up regulator (WUR). Depending on the model, the CPR
may be used to compensate for altitude, full load, and/or a cold engine. On cars
equipped with an oxygen sensor, the fuel mixture is adjusted by a device called the
frequency valve. The injectors are simple spring-loaded check valves with nozzles;
once fuel system pressure becomes high enough to overcome the counterspring, the
injectors begin spraying. K-Jetronic was used for many years between 1974 and the
mid 1990s by BMW, Lamborghini, Ferrari, Mercedes-
Benz, Volkswagen, Ford, Porsche, Audi, Saab, DeLorean, andVolvo. There was also
a variant of the system called KE-Jetronic with electronic instead of mechanical
control of the control pressure. Some Toyotas and other Japanese cars from the
1970s to the early 1990s used an application of Bosch's multipoint L-Jetronic system
manufactured under license by DENSO. Chrysler used a similar continuous fuel
injection system on the 1981-1983 Imperial.
In piston aircraft engines, continuous-flow fuel injection is the most common type. In
contrast to automotive fuel injection systems, aircraft continuous flow fuel injection is
all mechanical, requiring no electricity to operate. Two common types exist: the
Bendix RSA system, and the TCM system. The Bendix system is a direct descendant
of the pressure carburetor. However, instead of having a discharge valve in the barrel,
it uses a flow divider mounted on top of the engine, which controls the discharge rate
and evenly distributes the fuel to stainless steel injection lines which go to the intake
ports of each cylinder. The TCM system is even more simple. It has no venturi, no
pressure chambers, no diaphragms, and no discharge valve. The control unit is fed by
a constant-pressure fuel pump. The control unit simply uses a butterfly valve for the
air which is linked by a mechanical linkage to a rotary valve for the fuel. Inside the
control unit is another restriction which is used to control the fuel mixture. The
pressure drop across the restrictions in the control unit controls the amount of fuel
flowing, so that fuel flow is directly proportional to the pressure at the flow divider. In
fact, most aircraft using the TCM fuel injection system feature a fuel flow gauge which
is actually a pressure gauge that has been calibrated in gallons per hour or pounds
per hour of fuel.
Central port injection (CPI)
General Motors implemented a system called "central port injection" (CPI) or "central
port fuel injection" (CPFI). It uses tubes with poppet valves from a central injector to
spray fuel at each intake port rather than the central throttle-body[citation needed]. Pressure
specifications typically mirror that of a TBI system. The two variants were CPFI from
1992 to 1995, and CSFI from 1996 and on[citation needed]. CPFI is a batch-fire system, in
which fuel is injected to all ports simultaneously. The 1996 and later CSFI system
sprays fuel sequentially.[22]
Multi-point fuel injection
Multi-point fuel injection injects fuel into the intake ports just upstream of each
cylinder's intake valve, rather than at a central point within an intake manifold. MPFI
(or just MPI) systems can besequential, in which injection is timed to coincide with
each cylinder's intake stroke; batched, in which fuel is injected to the cylinders in
groups, without precise synchronization to any particular cylinder's intake stroke;
or simultaneous, in which fuel is injected at the same time to all the cylinders. The
intake is only slightly wet, and typical fuel pressure runs between 40-60 psi.
Many modern EFI systems utilize sequential MPFI; however, in newer gasoline
engines, direct injection systems are beginning to replace sequential ones.
Direct injection
Direct fuel injection costs more than indirect injection systems: the injectors are
exposed to more heat and pressure, so more costly materials and higher-precision
electronic management systems are required. However, the entire intake is dry,
making this a very clean system. In a common rail system, the fuel from the fuel tank
is supplied to the common header (called the accumulator). This fuel is then sent
through tubing to the injectors which inject it into the combustion chamber. The
header has a high pressure relief valve to maintain the pressure in the header and
return the excess fuel to the fuel tank. The fuel is sprayed with the help of a nozzle
which is opened and closed with a needle valve, operated with a solenoid. When the
solenoid is not activated, the spring forces the needle valve into the nozzle passage
and prevents the injection of fuel into the cylinder. The solenoid lifts the needle valve
from the valve seat, and fuel under pressure is sent in the engine cylinder. Third-
generation common rail diesels use piezoelectric injectors for increased precision,
with fuel pressures up to 1,800 bar/26,000 psi.
Gasoline engines incorporate gasoline direct injection engine technology.
Diesel engines
Diesel engines must use fuel injection, and it must be timed (unlike on petrol engines).
Throughout the early history of diesels, they were always fed by a mechanical pump
with a small separate cylinder for each cylinder, feeding separate fuel lines and
individual injectors. Most such pumps were in-line, though some were rotary.
Earlier systems, relying on crude injectors, often injected into a sub-chamber shaped
to swirl the compressed air and improve combustion; this was known as indirect
injection. However, it was less thermally efficient than the now universal direct
injection in which initiation of combustion takes place in a depression (often toroidal)
in the crown of the piston.
Petrol/gasoline engines
Main article: gasoline direct injection
Modern petrol engines (gasoline engines) also utilise direct injection, which is referred
to as gasoline direct injection. This is the next step in evolution from multi-point fuel
injection, and offers another magnitude of emission control by eliminating the "wet"
portion of the induction system along the inlet tract.
By virtue of better dispersion and homogeneity of the directly injected fuel, the cylinder
and piston are cooled, thereby permitting higher compression ratios and more
aggressive ignition timing, with resultant enhanced power output. More precise
management of the fuel injection event also enables better control of emissions.
Finally, the homogeneity of the fuel mixture allows for leaner air/fuel ratios, which
together with more precise ignition timing can improve fuel efficiency. Along with this,
the engine can operate with stratified (lean burn) mixtures, and hence avoid throttling
losses at low and part engine load. Some direct-injection systems
incorporate piezoelectronic fuel injectors. With their extremely fast response time,
multiple injection events can occur during each cycle of each cylinder of the engine.
The first use of direct petrol injection was on the Hesselman engine, invented by
Swedish engineer Jonas Hesselman in 1925.[23][24]
Maintenance hazards
Fuel injection introduces potential hazards in engine maintenance due to the high fuel
pressures used. Residual pressure can remain in the fuel lines long after an injection-
equipped engine has been shut down. This residual pressure must be relieved, and if
it is done so by external bleed-off, the fuel must be safely contained. If a high-
pressure diesel fuel injector is removed from its seat and operated in open air, there is
a risk to the operator of injury by hypodermic jet-injection, even with only 100 psi
(6.9 bar) pressure.[25] The first known such injury occurred in 1937 during a diesel
engine maintenance operation.[26]
Diesel Fuel Injection System
The diesel internal combustion engine differs from the gasoline powered Otto cycle by
using highly compressed hot air to ignite the fuel rather than using a spark plug
(compression ignition rather than spark ignition).
In the true diesel engine, only air is initially introduced into the combustion chamber.
The air is then compressed with a compression ratio typically between 15:1 and 22:1
resulting in 40-bar (4.0 MPa; 580 psi) pressure compared to 8 to 14 bars (0.80 to 1.4
MPa) (about 200 psi) in the petrol engine. This high compression heats the air to 550
°C (1,022 °F). At about the top of the compression stroke, fuel is injected directly into
the compressed air in the combustion chamber. This may be into a (typically toroidal)
void in the top of the piston or a pre-chamber depending upon the design of the
engine. The fuel injector ensures that the fuel is broken down into small droplets, and
that the fuel is distributed evenly. The heat of the compressed air vaporizes fuel from
the surface of the droplets. The vapour is then ignited by the heat from the
compressed air in the combustion chamber, the droplets continue to vaporise from
their surfaces and burn, getting smaller, until all the fuel in the droplets has been
burnt. The start of vaporisation causes a delay period during ignition and the
characteristic diesel knocking sound as the vapour reaches ignition temperature and
causes an abrupt increase in pressure above the piston. The rapid expansion of
combustion gases then drives the piston downward, supplying power to the
crankshaft.[23] Engines for scale-model aeroplanes use a variant of the Diesel principle
but premix fuel and air via a carburation system external to the combustion chambers.
As well as the high level of compression allowing combustion to take place without a
separate ignition system, a high compression ratio greatly increases the engine's
efficiency. Increasing the compression ratio in a spark-ignition engine where fuel and
air are mixed before entry to the cylinder is limited by the need to prevent
damaging pre-ignition. Since only air is compressed in a diesel engine, and fuel is not
introduced into the cylinder until shortly before top dead centre (TDC), premature
detonation is not an issue and compression ratios are much higher.
[edit]Early fuel injection systems
Diesel's original engine injected fuel with the assistance of compressed air, which
atomized the fuel and forced it into the engine through a nozzle (a similar principle to
an aerosol spray). The nozzle opening was closed by a pin valve lifted by the
camshaft to initiate the fuel injection before top dead centre (TDC). This is called an
air-blast injection. Driving the three stage compressor used some power but the
efficiency and net power output was more than any other combustion engine at that
time.
Diesel engines in service today raise the fuel to extreme pressures by mechanical
pumps and deliver it to the combustion chamber by pressure-activated injectors
without compressed air. With direct injected diesels, injectors spray fuel through 4 to
12 small orifices in its nozzle. The early air injection diesels always had a superior
combustion without the sharp increase in pressure during combustion. Research is
now being performed and patents are being taken out to again use some form of air
injection to reduce the nitrogen oxides and pollution, reverting to Diesel's original
implementation with its superior combustion and possibly quieter operation. In all
major aspects, the modern diesel engine holds true to Rudolf Diesel's original design,
that of igniting fuel by compression at an extremely high pressure within the cylinder.
With much higher pressures and high technology injectors, present-day diesel
engines use the so-called solid injection system applied by Herbert Akroyd Stuart for
his hot bulb engine. The indirect injection engine could be considered the latest
development of these low speed hot bulb ignition engines..
[edit]Fuel delivery
A vital component of all diesel engines is a mechanical or electronic governor which
regulates the idling speed and maximum speed of the engine by controlling the rate of
fuel delivery. Unlike Otto-cycle engines, incoming air is not throttled and a diesel
engine without a governor cannot have a stable idling speed and can easily
overspeed, resulting in its destruction. Mechanically governed fuel injection systems
are driven by the engine's gear train.[24] These systems use a combination of springs
and weights to control fuel delivery relative to both load and speed.[24] Modern
electronically controlled diesel engines control fuel delivery by use of an electronic
control module (ECM) or electronic control unit (ECU). The ECM/ECU receives an
engine speed signal, as well as other operating parameters such as intake manifold
pressure and fuel temperature, from a sensor and controls the amount of fuel and
start of injection timing through actuators to maximise power and efficiency and
minimise emissions. Controlling the timing of the start of injection of fuel into the
cylinder is a key to minimizing emissions, and maximizing fuel economy (efficiency),
of the engine. The timing is measured in degrees of crank angle of the piston before
top dead centre. For example, if the ECM/ECU initiates fuel injection when the piston
is 10 degrees before TDC, the start of injection, or timing, is said to be 10° BTDC.
Optimal timing will depend on the engine design as well as its speed and load.
Advancing the start of injection (injecting before the piston reaches to its SOI-TDC)
results in higher in-cylinder pressure and temperature, and higher efficiency, but also
results in elevated engine noise and increased oxides of nitrogen (NOx) emissions due
to higher combustion temperatures. Delaying start of injection causes incomplete
combustion, reduced fuel efficiency and an increase in exhaust smoke, containing a
considerable amount of particulate matter and unburned hydrocarbons.
[edit]Major advantages
Diesel engines have several advantages over other internal combustion engines:
They burn less fuel than a petrol engine performing the same work, due to the
engine's higher temperature of combustion and greater expansion ratio.[1] Gasoline
engines are typically 30 percent efficient while diesel engines can convert over 45
percent of the fuel energy into mechanical energy[25] (see Carnot cycle for further
explanation).
They have no high voltage electrical ignition system, resulting in high reliability
and easy adaptation to damp environments. The absence of coils, spark plug
wires, etc., also eliminates a source of radio frequency emissions which can
interfere with navigation and communication equipment, which is especially
important in marine and aircraft applications.
The life of a diesel engine is generally about twice as long as that of a petrol
engine[26] due to the increased strength of parts used. Diesel fuel has better
lubrication properties than petrol as well.
Bus powered by biodiesel
Diesel fuel is distilled directly from petroleum. Distillation yields some gasoline,
but the yield would be inadequate without catalytic reforming, which is a more
costly process.
Diesel fuel is considered safer than petrol in many applications. Although diesel
fuel will burn in open air using a wick, it will not explode and does not release a
large amount of flammable vapor. The low vapor pressure of diesel is especially
advantageous in marine applications, where the accumulation of explosive fuel-air
mixtures is a particular hazard. For the same reason, diesel engines are immune
to vapor lock.
For any given partial load the fuel efficiency (mass burned per energy
produced) of a diesel engine remains nearly constant, as opposed to petrol and
turbine engines which use proportionally more fuel with partial power outputs.[27][28]
[29][30]
They generate less waste heat in cooling and exhaust.[1]
Diesel engines can accept super- or turbo-charging pressure without any
natural limit, constrained only by the strength of engine components. This is unlike
petrol engines, which inevitably suffer detonation at higher pressure.
The carbon monoxide content of the exhaust is minimal, therefore diesel
engines are used in underground mines.[31]
Biodiesel is an easily synthesized, non-petroleum-based fuel
(through transesterification) which can run directly in many diesel engines, while
gasoline engines either need adaptation to runsynthetic fuels or else use them as
an additive to gasoline (e.g., ethanol added to gasohol).
[edit]Mechanical and electronic injection
Many configurations of fuel injection have been used over the past century (1901–
2000).
Most present day (2008) diesel engines make use of a camshaft, rotating at half
crankshaft speed, lifted mechanical single plunger high-pressure fuel pump driven by
the engine crankshaft. For each engine cylinder, the corresponding plunger in the fuel
pump measures out the correct amount of fuel and determines the timing of each
injection. These engines use injectors that are very precise spring-loaded valves that
open and close at a specific fuel pressure. Separate high-pressure fuel lines connect
the fuel pump with each cylinder. Fuel volume for each single combustion is controlled
by a slanted groove in the plunger which rotates only a few degrees releasing the
pressure and is controlled by a mechanical governor, consisting of weights rotating at
engine speed constrained by springs and a lever. The injectors are held open by the
fuel pressure. On high-speed engines the plunger pumps are together in one unit.[32] The length of fuel lines from the pump to each injector is normally the same for
each cylinder in order to obtain the same pressure delay.
A cheaper configuration on high-speed engines with fewer than six cylinders is to use
an axial-piston distributor pump, consisting of one rotating pump plunger delivering
fuel to a valve and line for each cylinder (functionally analogous to points and
distributor cap on an Otto engine).[24]
Many modern systems have a single fuel pump which supplies fuel constantly at high
pressure with a common rail (single fuel line common) to each injector. Each injector
has a solenoid operated by an electronic control unit, resulting in more accurate
control of injector opening times that depend on other control conditions, such as
engine speed and loading, and providing better engine performance and fuel
economy. This design is also mechanically simpler than the combined pump and
valve design, making it generally more reliable, and less loud, than its mechanical
counterpart.[citation needed] This system does have have the drawback of requiring a
reliable electrical system for operation.
Both mechanical and electronic injection systems can be used in
either direct or indirect injection configurations.
Older diesel engines with mechanical injection pumps could be inadvertently run in
reverse, albeit very inefficiently. When this occurs, massive amounts of soot are
ejected from the air intake. This was often a consequence of push starting a vehicle
using the wrong gear. Large ship diesels are capable of running either direction.
[edit]Indirect injectionMain article: Indirect injection
An indirect injection diesel engine delivers fuel into a chamber off the combustion
chamber, called a pre-chamber or ante-chamber, where combustion begins and then
spreads into the main combustion chamber, assisted by turbulence created in the
chamber. This system allows for a smoother, quieter running engine, and because
combustion is assisted by turbulence, injector pressures can be lower, about 100 bar
(10 MPa; 1,500 psi), using a single orifice tapered jet injector. Mechanical injection
systems allowed high-speed running suitable for road vehicles (typically up to speeds
of around 4,000 rpm). The pre-chamber had the disadvantage of increasing heat loss
to the engine's cooling system, and restricting the combustion burn, which reduced
the efficiency by 5–10 percent.[33] Indirect injection engines were used in small-
capacity, high-speed diesel engines in automotive, marine and construction uses from
the 1950s, until direct injection technology advanced in the 1980s[citation needed]. Indirect
injection engines are cheaper to build and it is easier to produce smooth, quiet-
running vehicles with a simple mechanical system. In road-going vehicles most prefer
the greater efficiency and better controlled emission levels of direct injection. Indirect
injection diesels can still be found in the many ATV diesel applications.
[edit]Direct injection
Direct injection diesel engines have injectors mounted at the top of the combustion
chamber. The injectors are activated using one of two methods - hydraulic pressure
from the fuel pump, or an electonic signal from an engine controller.
Hydraulic pressure activated injectors can produce harsh engine noise. Fuel
consumption was about 15 to 20 percent lower than indirect injection diesels. The
extra noise was generally not a problem for industrial uses of the engine. But for
automotive usage, buyers had to decide whether or not the increased fuel efficiency
would compensate for the extra noise.
Electronic control of the fuel injection transformed the direct injection engine. This was
pioneered by Fiat in 1986 (Croma). The injection pressure remained around 300 bar
(30 MPa; 4,400 psi), but the injection timing fuel quantity, EGR, and turbo boost are all
electronically controlled. This gives more precise control of these parameters,
resulting in lowered emissions and quieter, smoother running engines.[citation needed]
[edit]Unit direct injectionMain article: Unit Injector
Unit direct injection also injects fuel directly into the cylinder of the engine. In this
system the injector and the pump are combined into one unit positioned over each
cylinder controlled by the camshaft. Each cylinder has its own unit eliminating the
high-pressure fuel lines, achieving a more consistent injection. This type of injection
system, also developed by Bosch, is used by Volkswagen AG in cars (where it is
called a Pumpe-Düse-System—literally pump-nozzle system) and by Mercedes Benz
("PLD") and most major diesel engine manufacturers in large commercial engines
(CAT, Cummins,Detroit Diesel, Volvo). With recent advancements, the pump pressure
has been raised to 2,400 bar (240 MPa; 35,000 psi),[34] allowing injection parameters
similar to common rail systems.[35]
[edit]Common rail direct injectionMain article: Common rail
In common rail systems, the separate pulsing high-pressure fuel line to each cylinder's
injector is also eliminated. Instead, a high-pressure pump pressurizes fuel at up to
2,500 bar (250 MPa; 36,000 psi),[36] in a "common rail". The common rail is a tube that
supplies each computer-controlled injector containing a precision-machined nozzle
and a plunger driven by a solenoid or piezoelectricactuator.
[edit]Cold weather[edit]Starting
In cold weather, high speed diesel engines can be difficult to start because the mass
of the cylinder block and cylinder head absorb the heat of compression, preventing
ignition due to the higher surface-to-volume ratio. Pre-chambered engines make use
of small electric heaters inside the pre-chambers called glowplugs, while the direct-
injected engines have these glowplugs in the combustion chamber. These engines
also generally have a higher compression ratio of 19:1 to 21:1. Low-speed and
compressed-air-started larger and intermediate-speed diesels do not have glowplugs
and compression ratios are around 16:1.[citation needed]
Some engines (e.g., some Cummins models) use resistive grid heaters in the intake
manifold to warm the inlet air until the engine reaches operating temperature. Engine
block heaters (electric resistive heaters in the engine block) connected to the utility
grid are often used when an engine is turned off for extended periods (more than an
hour) in cold weather to reduce startup time and engine wear. Block heaters are also
used for emergency power standby Diesel-powered generators which must rapidly
pick up load on a power failure. In the past, a wider variety of cold-start methods were
used. Some engines, such as Detroit Diesel [37] engines and Lister-Petter engines,
used[when?] a system to introduce small amounts of ether into the inlet manifold to start
combustion.[citation needed]Saab-Scania marine engines, Field Marshall tractors (among
others) used slow-burning solid-fuel 'cigarettes' which were fitted into the cylinder
head as a primitive glow plug.[citation needed]
Lucas developed the Thermostart, where an electrical heating element was combined
with a small fuel valve in the inlet manifold. Diesel fuel slowly dripped from the valve
onto the hot element and ignited. The flame heated the inlet manifold and when the
engine was cranked, the flame was drawn into the cylinders to start combustion.[citation
needed]
International Harvester developed a tractor in the 1930s that had a 7-litre 4-cylinder
engine which started as a gasoline engine and ran on diesel after warming up. The
cylinder head had valves which opened for a portion of the compression stroke to
reduce the effective compression ratio, and a magneto produced the spark. An
automatic ratchet system automatically disengaged the ignition system and closed the
valves once the engine had run for 30 seconds. The operator then switched off the
petrol fuel system and opened the throttle on the diesel injection system.[citation needed]
Recent direct-injection systems[which?] are advanced to the extent that pre-chambers
systems are not needed by using a common rail fuel system with electronic fuel
injection.[citation needed]
[edit]Gelling
Diesel fuel is also prone to waxing or gelling in cold weather; both are terms for the
solidification of diesel oil into a partially crystalline state. The crystals build up in the
fuel line (especially in fuel filters), eventually starving the engine of fuel and causing it
to stop running. Low-output electric heaters in fuel tanks and around fuel lines are
used to solve this problem. Also, most engines have a spill return system, by which
any excess fuel from the injector pump and injectors is returned to the fuel tank. Once
the engine has warmed, returning warm fuel prevents waxing in the tank. Due to
improvements in fuel technology with additives, waxing rarely occurs in all but the
coldest weather when a mix of diesel and kerosene should be used to run a vehicle.
[edit]Types
[edit]Size Groups
Two Cycle Diesel engine with Roots blower, typical of Locomotive Engines
There are three size groups of Diesel engines[38]
Small - Under 188 kW output
Medium
Large
[edit]Basic Types of Diesel Engines
There are two basic types of Diesel Engines[38]
Four Cycle
Two Cycle
[edit]Early
Rudolf Diesel based his engine on the design of the Gas engine created by Nikolaus
Otto in 1876 with the goal of improving its efficiency. He patented his Diesel engine
concepts in patents that were set forth in 1892 and 1893.[39] As such, diesel engines in
the late 19th and early 20th centuries used the same basic layout and form as
industrial steam engines, with long-bore cylinders, external valve gear, cross-head
bearings and an open crankshaft connected to a large flywheel.[dubious – discuss] Smaller
engines would be built with vertical cylinders, while most medium- and large-sized
industrial engines were built with horizontal cylinders, just as steam engines had
been. Engines could be built with more than one cylinder in both cases. The largest
early diesels resembled the triple-expansion steam reciprocating engine, being tens of
feet high with vertical cylinders arranged in-line. These early engines ran at very slow
speeds—partly due to the limitations of their air-blast injector equipment and partly so
they would be compatible with the majority of industrial equipment designed for steam
engines; maximum speeds of between 100 and 300 rpm were common. Engines were
usually started by allowing compressed air into the cylinders to turn the engine,
although smaller engines could be started by hand.[40]
In 1897 when the first Diesel engine was completed Adolphus Busch traveled to
Cologne and negotiated exclusive right to produce the Diesel engine in the USA and
Canada. In his examination of the engine it was noted that the Diesel at that time
operated at efficiencies of 32 to 35 percent thermodynamic efficiency when a typical
triple expansion steam engine would operate at about 18 percent.[10]
In the early decades of the 20th century, when large diesel engines were first being
used, the engines took a form similar to the compound steam engines common at the
time, with the piston being connected to the connecting rod by a crosshead bearing.
Following steam engine practice some manufactures made double-acting two-stroke
and four-stroke diesel engines to increase power output, with combustion taking place
on both sides of the piston, with two sets of valve gear and fuel injection. While it
produced large amounts of power and was very efficient, the double-acting diesel
engine's main problem was producing a good seal where the piston rod passed
through the bottom of the lower combustion chamber to the crosshead bearing, and
no more were built. By the 1930s turbochargers were fitted to some engines.
Crosshead bearings are still used to reduce the wear on the cylinders in large long-
stroke main marine engines.
[edit]Modern
A Yanmar 2GM20 marine diesel engine, installed in a sailboat
As with petrol engines, there are two classes of diesel engines in current use: two-
stroke and four-stroke. The four-stroke type is the "classic" version, tracing its lineage
back to Rudolf Diesel's prototype. It is also the most commonly used form, being the
preferred power source for many motor vehicles, especially buses and trucks. Much
larger engines, such as used for railroad locomotion and marine propulsion, are often
two-stroke units, offering a more favourablepower-to-weight ratio, as well as better
fuel economy. The most powerful engines in the world are two-stroke diesels of
mammoth dimensions.[41]
Two-stroke diesel engine operation is similar to that of petrol counterparts, except that
fuel is not mixed with air before induction, and the crankcase does not take an active
role in the cycle. The traditional two-stroke design relies upon a mechanically
driven positive displacement blower to charge the cylinders with air before
compression and ignition. The charging process also assists in expelling
(scavenging) combustion gases remaining from the previous power stroke.
The archetype of the modern form of the two-stroke diesel is the Detroit
Diesel engine, in which the blower pressurizes a chamber in the engine block that is
often referred to as the "air box". The (much larger) Electro-Motive prime mover used
in EMD diesel-electric locomotives is built to the same principle.
In a two-stroke diesel engine, as the cylinder's piston approaches the bottom dead
centre exhaust ports or valves are opened relieving most of the excess pressure after
which a passage between the air box and the cylinder is opened, permitting air flow
into the cylinder.[42][43] The air flow blows the remaining combustion gases from the
cylinder—this is the scavenging process. As the piston passes through bottom centre
and starts upward, the passage is closed and compression commences, culminating
in fuel injection and ignition. Refer to two-stroke diesel engines for more detailed
coverage of aspiration types and supercharging of two-stroke diesel engines.
Normally, the number of cylinders are used in multiples of two, although any number
of cylinders can be used as long as the load on the crankshaft is counterbalanced to
prevent excessive vibration. The inline-six-cylinder design is the most prolific in light-
to medium-duty engines, though small V8 and larger inline-four displacement engines
are also common. Small-capacity engines (generally considered to be those below
five litres in capacity) are generally four- or six-cylinder types, with the four-cylinder
being the most common type found in automotive uses. Five-cylinder diesel engines
have also been produced, being a compromise between the smooth running of the
six-cylinder and the space-efficient dimensions of the four-cylinder. Diesel engines for
smaller plant machinery, boats, tractors, generators and pumps may be four-, three-
or two-cylinder types, with the single-cylinder diesel engine remaining for light
stationary work. Direct reversible two-stroke marine diesels need at least three
cylinders for reliable restarting forwards and reverse, while four-stroke diesels need at
least six cylinders.
The desire to improve the diesel engine's power-to-weight ratio produced several
novel cylinder arrangements to extract more power from a given capacity. The
uniflow opposed-piston engine uses two pistons in one cylinder with the combustion
cavity in the middle and gas in- and outlets at the ends. This makes a comparatively
light, powerful, swiftly running and economic engine suitable for use in aviation. An
example is the Junkers Jumo 204/205. The Napier Deltic engine, with three cylinders
arranged in a triangular formation, each containing two opposed pistons, the whole
engine having three crankshafts, is one of the better known.
[edit]Low-speed diesels
Low-speed diesel engines (as used in ships and other applications where overall
engine weight is relatively unimportant) often have a thermal efficiency which exceeds
50 percent.[1][2]
[edit]Gas generatorMain article: Free-piston engine
Before 1950, Sulzer started experimenting with two-stroke engines with boost
pressures as high as 6 atmospheres, in which all the output power was taken from an
exhaust gas turbine. The two-stroke pistons directly drove air compressor pistons to
make a positive displacement gas generator. Opposed pistons were connected by
linkages instead of crankshafts. Several of these units could be connected to provide
power gas to one large output turbine. The overall thermal efficiency was roughly
twice that of a simple gas turbine.[44] This system was derived from Raúl Pateras
Pescara's work on free-piston engines in the 1930s.
[edit]Advantages and disadvantages versus spark-ignition engines
This section needs additional citations for verification. Please help improve
this article by adding citations to reliable sources. Unsourced material may
be challenged and removed. (February 2011)
[edit]Power and fuel economy
The MAN S80ME-C7 low speed diesel engines use 155 gram fuel per kWh for an
overall energy conversion efficiency of 54.4 percent, which is the highest conversion
of fuel into power by any internal orexternal combustion engine.[1] Diesel engines are
more efficient than gasoline (petrol) engines of the same power rating, resulting in
lower fuel consumption. A common margin is 40 percent more miles per gallon for an
efficient turbodiesel. For example, the current model Škoda Octavia,
using Volkswagen Group engines, has a combined Euro rating of 6.2 L/100 km
(38 miles per US gallon, 16 km/L) for the 102 bhp (76 kW) petrol engine and
4.4 L/100 km (54 mpg, 23 km/L) for the 105 bhp (78 kW) diesel engine.
However, such a comparison does not take into account that diesel fuel is denser and
contains about 15 percent more energy by volume. Although the calorific value of the
fuel is slightly lower at 45.3 MJ/kg (megajoules per kilogram) than petrol at
45.8 MJ/kg, liquid diesel fuel is significantly denser than liquid petrol. This is significant
because volume of fuel, in addition to mass, is an important consideration in mobile
applications. No vehicle has an unlimited volume available for fuel storage.
Adjusting the numbers to account for the energy density of diesel fuel, the overall
energy efficiency is still about 20 percent greater for the diesel version.
While a higher compression ratio is helpful in raising efficiency, diesel engines are
much more efficient than gasoline (petrol) engines when at low power and at engine
idle. Unlike the petrol engine, diesels lack a butterfly valve (throttle) in the inlet
system, which closes at idle. This creates parasitic loss and destruction of availability
of the incoming air, reducing the efficiency of petrol engines at idle. In many
applications, such as marine, agriculture, and railways, diesels are left idling and
unattended for many hours, sometimes even days. These advantages are especially
attractive in locomotives (see dieselisation).
The average diesel engine has a poorer power-to-weight ratio than the petrol engine.
This is because the diesel must operate at lower engine speeds[45] and because it
needs heavier, stronger parts to resist the operating pressure caused by the high
compression ratio of the engine and the large amounts of torque generated to the
crankshaft. In addition, diesels are often built with stronger parts to give them longer
lives and better reliability, important considerations in industrial applications.
For most industrial or nautical applications, reliability is considered more important
than light weight and high power. Diesel fuel is injected just before the power stroke.
As a result, the fuel cannot burn completely unless it has a sufficient amount of
oxygen. This can result in incomplete combustion and black smoke in the exhaust if
more fuel is injected than there is air available for the combustion process. Modern
engines with electronic fuel delivery can adjust the timing and amount of fuel delivery
(by changing the duration of the injection pulse), and so operate with less waste of
fuel. In a mechanical system, the injection timing and duration must be set to be
efficient at the anticipated operating rpm and load, and so the settings are less than
ideal when the engine is running at any other RPM than what it is timed for. The
electronic injection can "sense" engine revs, load, even boost and temperature, and
continuously alter the timing to match the given situation. In the petrol engine, air and
fuel are mixed for the entire compression stroke, ensuring complete mixing even at
higher engine speeds.
Diesel engines usually have longer stroke lengths in order to achieve the necessary
compression ratios. As a result piston and connecting rods are heavier and more
force must be transmitted through the connecting rods and crankshaft to change the
momentum of the piston. This is another reason that a diesel engine must be stronger
for the same power output as a petrol engine.
Yet it is this characteristic that has allowed some enthusiasts to acquire significant
power increases with turbocharged engines by making fairly simple and inexpensive
modifications. A petrol engine of similar size cannot put out a comparable power
increase without extensive alterations because the stock components cannot
withstand the higher stresses placed upon them. Since a diesel engine is already built
to withstand higher levels of stress, it makes an ideal candidate for performance
tuning at little expense. However, it should be said that any modification that raises
the amount of fuel and air put through a diesel engine will increase its operating
temperature, which will reduce its life and increase service requirements. These are
issues with newer, lighter, high-performance diesel engines which are not "overbuilt"
to the degree of older engines and they are being pushed to provide greater power in
smaller engines. The addition of a turbocharger or supercharger to the engine greatly
assists in increasing fuel economy and power output, mitigating the fuel-air intake
speed limit mentioned above for a given engine displacement. Boost pressures can
be higher on diesels than on petrol engines, due to the latter's susceptibility to knock,
and the higher compression ratio allows a diesel engine to be more efficient than a
comparable spark ignition engine. Because the burned gases are expanded further in
a diesel engine cylinder, the exhaust gas is cooler, meaning turbochargers require
less cooling, and can be more reliable, than with spark-ignition engines.
With a diesel, boost pressure is essentially unlimited. It is literally possible to run as
much boost as the engine will physically stand before breaking apart.
The increased fuel economy of the diesel engine over the petrol engine means that
the diesel produces less carbon dioxide (CO2) per unit distance. Recent advances in
production and changes in the political climate have increased the availability and
awareness of biodiesel, an alternative to petroleum-derived diesel fuel with a much
lower net-sum emission of CO2, due to the absorption of CO2 by plants used to
produce the fuel. Although concerns are now being raised as to the negative effect
this is having on the world food supply, as the growing of crops specifically
for biofuels takes up land that could be used for food crops and uses water that could
be used by both humans and animals. However, the use of waste vegetable oil,
sawmill waste from managed forests in Finland, and advances in the production of
vegetable oil from algae demonstrate great promise in providing feed stocks for
sustainable biodiesel that are not in competition with food production.
Diesel engines have a lower rotational speed than an equivalent size petrol engine
because the diesel-air mixture burns slower than the petrol-air mixture.[citation needed] A
combination of improved mechanical technology (such as multi-stage injectors which
fire a short "pilot charge" of fuel into the cylinder to warm the combustion chamber
before delivering the main fuel charge), higher injection pressures that have improved
the atomisation of fuel into smaller droplets, and electronic control (which can adjust
the timing and length of the injection process to optimise it for all speeds and
temperatures) have mitigated most of these problems in the latest generation of
common-rail designs, while greatly improving engine efficiency. Poor power and
narrow torque bands have been addressed by superchargers, turbochargers,
(especially variable geometry turbochargers), intercoolers, and a large efficiency
increase from about 35 percent for IDI to 45 percent for the latest engines in the last
15 years.
Even though diesel engines have a theoretical fuel efficiency of 75 percent, in practice
it is lower. Engines in large diesel trucks, buses, and newer diesel cars can achieve
peak efficiencies around 45 percent,[46] and could reach 55 percent efficiency in the
near future.[47] However, average efficiency over a driving cycle is lower than peak
efficiency. For example, it might be 37 percent for an engine with a peak efficiency of
44 percent.[48]
[edit]EmissionsMain article: Diesel exhaust
In diesel engines, conditions in the engine differ from the spark-ignition engine, since
power is directly controlled by the fuel supply, rather than by controlling the air supply.
Thus when the engine runs at low power, there is enough oxygen present to burn the
fuel, and diesel engines only make significant amounts of carbon monoxide when
running under a load.
Diesel exhaust is well known for its characteristic smell; but in Britain this smell in
recent years has become much less because the sulfur is now removed from the fuel
in the oil refinery.
Diesel exhaust has been found to contain a long list of toxic air contaminants. Among
these pollutants, fine particle pollution is perhaps the most important as a cause
of diesel's harmful health effects.
[edit]Power and torque
For commercial uses requiring towing, load carrying and other tractive tasks, diesel
engines tend to have better torque characteristics. Diesel engines tend to have their
torque peak quite low in their speed range (usually between 1600 and 2000 rpm for a
small-capacity unit, lower for a larger engine used in a truck). This provides smoother
control over heavy loads when starting from rest, and, crucially, allows the diesel
engine to be given higher loads at low speeds than a petrol engine, making them
much more economical for these applications. This characteristic is not so desirable in
private cars, so most modern diesels used in such vehicles use electronic
control, variable geometry turbochargers and shorter piston strokes to achieve a wider
spread of torque over the engine's speed range, typically peaking at around 2500–
3000 rpm.
While diesel engines tend to have more torque at lower engine speeds than petrol
engines, diesel engines tend to have a narrower power band than petrol engines.
Naturally aspirated diesels tend to lack power and torque at the top of their speed
range. This narrow band is a reason why a vehicle such as a truck may have
a gearbox with as many as 18 or more gears, to allow the engine's power to be used
effectively at all speeds. Turbochargers tend to improve power at high engine speeds;
superchargers improve power at lower speeds; and variable geometry turbochargers
improve the engine's performance equally by flattening the torque curve.
[edit]Noise
The characteristic noise of a diesel engine is variably called diesel clatter, diesel
nailing, or diesel knock.[49] Diesel clatter is caused largely by the diesel combustion
process; the sudden ignition of the diesel fuel when injected into the combustion
chamber causes a pressure wave. Engine designers can reduce diesel clatter
through: indirect injection; pilot or pre-injection; injection timing; injection rate;
compression ratio; turbo boost; and exhaust gas recirculation (EGR).[50] Common rail
diesel injection systems permit multiple injection events as an aid to noise reduction.
Diesel fuels with a higher cetane rating modify the combustion process and reduce
diesel clatter.[49] CN (Cetane number) can be raised by distilling higher quality crude
oil, by catalyzing a higher quality product or by using a cetane improving additive.
Some oil companies market high cetane or premium diesel. Biodiesel has a higher
cetane number than petrodiesel, typically 55CN for 100% biodiesel.[citation needed]
A combination of improved mechanical technology such as multi-stage injectors which
fire a short "pilot charge" of fuel into the cylinder to initiate combustion before
delivering the main fuel charge, higher injection pressures that have improved the
atomisation of fuel into smaller droplets, and electronic control (which can adjust the
timing and length of the injection process to optimise it for all speeds and
temperatures), have partially mitigated these problems in the latest generation of
common-rail designs, while improving engine efficiency.
[edit]Reliability
The lack of an electrical ignition system greatly improves the reliability. The high
durability of a diesel engine is also due to its overbuilt nature (see above), a benefit
that is magnified by the lower rotating speeds in diesels. Diesel fuel is a better
lubricant than petrol so is less harmful to the oil film on piston
rings and cylinder bores; it is routine for diesel engines to cover 250,000 miles
(400,000 km) or more without a rebuild.
Due to the greater compression force required and the increased weight of the
stronger components, starting a diesel engine is harder. More torque is required to
push the engine through compression.
Either an electrical starter or an air-start system is used to start the engine turning. On
large engines, pre-lubrication and slow turning of an engine, as well as heating, are
required to minimise the amount of engine damage during initial start-up and running.
Some smaller military diesels can be started with an explosive cartridge, called
a Coffman starter, which provides the extra power required to get the machine turning.
In the past, Caterpillar and John Deere used a small petrol pony engine in their
tractors to start the primary diesel engine. The pony engine heated the diesel to aid in
ignition and used a small clutch and transmission to spin up the diesel engine. Even
more unusual was an International Harvester design in which the diesel engine had its
own carburetor and ignition system, and started on petrol. Once warmed up, the
operator moved two levers to switch the engine to diesel operation, and work could
begin. These engines had very complex cylinder heads, with their own petrol
combustion chambers, and were vulnerable to expensive damage if special care was
not taken (especially in letting the engine cool before turning it off).
[edit]Quality and variety of fuels
Petrol/gasoline engines are limited in the variety and quality of the fuels they can burn.
Older petrol engines fitted with a carburetor required a volatile fuel that would vaporise
easily to create the necessary air-fuel ratio for combustion. Because both air and fuel
are admitted to the cylinder, if the compression ratio of the engine is too high or the
fuel too volatile (with too low an octane rating), the fuel will ignite under compression,
as in a diesel engine, before the piston reaches the top of its stroke. This pre-ignition
causes a power loss and over time major damage to the piston and cylinder. The
need for a fuel that is volatile enough to vaporise but not too volatile (to avoid pre-
ignition) means that petrol engines will only run on a narrow range of fuels. There has
been some success at dual-fuel engines that use petrol and ethanol, petrol
and propane, and petrol and methane.
In diesel engines, a mechanical injector system vaporizes the fuel directly into the
combustion chamber or a pre-combustion chamber (as opposed to a Venturi jet in a
carburetor, or a fuel injector in a fuel injection system vaporising fuel into the intake
manifold or intake runners as in a petrol engine). This forced vaporisation means that
less-volatile fuels can be used. More crucially, because only air is inducted into the
cylinder in a diesel engine, the compression ratio can be much higher as there is no
risk of pre-ignition provided the injection process is accurately timed. This means that
cylinder temperatures are much higher in a diesel engine than a petrol engine,
allowing less volatile fuels to be used.
Diesel fuel is a form of light fuel oil, very similar to kerosene/paraffin, but diesel
engines, especially older or simple designs that lack precision electronic injection
systems, can run on a wide variety of other fuels. Some of the most common
alternatives are Jet A-1 type jet fuel or vegetable oil from a very wide variety of plants.
Some engines can be run on vegetable oil without modification, and most others
require fairly basic alterations. Biodiesel is a pure diesel-like fuel refined from
vegetable oil and can be used in nearly all diesel engines. Requirements for fuels to
be used in diesel engines are the ability of the fuel to flow along the fuel lines, the
ability of the fuel to lubricate the injector pump and injectors adequately, and its
ignition qualities (ignition delay, cetane number). Inline mechanical injector pumps
generally tolerate poor-quality or bio-fuels better than distributor-type pumps. Also,
indirect injection engines generally run more satisfactorily on bio-fuels than direct
injection engines. This is partly because an indirect injection engine has a much
greater 'swirl' effect, improving vaporisation and combustion of fuel, and because (in
the case of vegetable oil-type fuels) lipid depositions can condense on the cylinder
walls of a direct-injection engine if combustion temperatures are too low (such as
starting the engine from cold).
It is often reported that Diesel designed his engine to run on peanut oil. Diesel stated
in his published papers, "at the Paris Exhibition in 1900 (Exposition Universelle) there
was shown by the Otto Company a small diesel engine, which, at the request of the
French Government ran on Arachide (earth-nut or pea-nut) oil (see biodiesel), and
worked so smoothly that only a few people were aware of it. The engine was
constructed for using mineral oil, and was then worked on vegetable oil without any
alterations being made. The French Government at the time thought of testing the
applicability to power production of the Arachide, or earth-nut, which grows in
considerable quantities in their African colonies, and can easily be cultivated there."
Diesel himself later conducted related tests and appeared supportive of the idea.[51]
Most large marine diesels (sometimes called cathedral engines due to their size[citation
needed]) run on heavy fuel oil (sometimes called "bunker oil"), which is a thick, viscous
and almost flameproof fuel which is very safe to store and cheap to buy in bulk as it is
a waste product from the petroleum refining industry. The fuel must be heated to thin
it out (often by the exhaust header) and is often passed through multiple injection
stages to vaporise it.
[edit]Fuel and fluid characteristics
Main article: Diesel fuel
Diesel engines can operate on a variety of different fuels, depending on configuration,
though the eponymous diesel fuel derived from crude oil is most common. The
engines can work with the full spectrum of crude oil distillates, from natural gas,
alcohols, petrol, wood gas to the fuel oils from diesel oil to residual fuels.[52]
The type of fuel used is a combination of service requirements, and fuel costs. Good-
quality diesel fuel can be synthesised from vegetable oil and alcohol. Diesel fuel can
be made from coal or other carbon base using the Fischer-Tropsch
process. Biodiesel is growing in popularity since it can frequently be used in
unmodified engines, though production remains limited. Recently, biodiesel from
coconut, which can produce a very promising coco methyl ester (CME), has
characteristics which enhance lubricity and combustion giving a regular diesel engine
without any modification more power, less particulate matter or black smoke, and
smoother engine performance. The Philippines pioneers in the research on Coconut
based CME with the help of German and American scientists. Petroleum-derived
diesel is often called petrodiesel if there is need to distinguish the source of the fuel.
Pure plant oils are increasingly being used as a fuel for cars, trucks and
remote combined heat and power generation especially in Germany where hundreds
of decentralised small- and medium-sized oil presses cold press oilseed,
mainly rapeseed, for fuel. There is a Deutsches Institut für Normung fuel standard
for rapeseed oil fuel.
Residual fuels are the "dregs" of the distillation process and are a thicker, heavier oil,
or oil with higher viscosity, which are so thick that they are not readily pumpable
unless heated. Residual fuel oils are cheaper than clean, refined diesel oil, although
they are dirtier. Their main considerations are for use in ships and very large
generation sets, due to the cost of the large volume of fuel consumed, frequently
amounting to many tonnes per hour. The poorly refined biofuels straight vegetable
oil (SVO) and waste vegetable oil (WVO) can fall into this category, but can be viable
fuels on non common rail or TDI PD diesels with the simple conversion of fuel heating
to 80 to 100 degrees Celsius to reduce viscosity, and adequate filtration to OEM
standards. Engines using these heavy oils have to start and shut down on standard
diesel fuel, as these fuels will not flow through fuel lines at low temperatures. Moving
beyond that, use of low-grade fuels can lead to serious maintenance problems
because of their high sulphur and lower lubrication properties. Most diesel engines
that power ships like supertankers are built so that the engine can safely use low-
grade fuels due to their separate cylinder and crankcase lubrication.
Normal diesel fuel is more difficult to ignite and slower in developing fire than petrol
because of its higher flash point, but once burning, a diesel fire can be fierce.
Fuel contaminants such as dirt and water are often more problematic in diesel
engines than in petrol engines. Water can cause serious damage, due to corrosion, to
the injection pump and injectors; and dirt, even very fine particulate matter, can
damage the injection pumps due to the close tolerances that the pumps are machined
to. All diesel engines will have a fuel filter (usually much finer than a filter on a petrol
engine), and a water trap. The water trap (which is sometimes part of the fuel filter)
often has a float connected to a warning light, which warns when there is too much
water in the trap, and must be drained before damage to the engine can result. The
fuel filter must be replaced much more often on a diesel engine than on a petrol
engine, changing the fuel filter every 2-4 oil changes is not uncommon for some
vehicles.
[edit]Safety
[edit]Fuel flammability
Diesel fuel has low flammability, leading to a low risk of fire caused by fuel in a vehicle
equipped with a diesel engine.
In yachts diesels are used because petrol engines generate combustible vapors,
which can accumulate in the bottom of the vessel, sometimes causing explosions.
Therefore ventilation systems on petrol powered vessels are required.[53]
The United States Army and NATO use only diesel engines and turbines because of
fire hazard. Although neither gasoline nor diesel is explosive in liquid form, both can
create an explosive air/vapor mix under the right conditions. However, diesel fuel is
less prone due to its lower vapor pressure, which is an indication of evaporation rate.
The Material Safety Data Sheet[54] for ultra-low sulfur diesel fuel indicates a vapor
explosion hazard for diesel indoors, outdoors, or in sewers.
US Army gasoline-engined tanks during World War II were nicknamed Ronsons,
because of their greater likelihood of catching fire when damaged by enemy fire.
(Although tank fires were usually caused by detonation of the ammunition rather than
fuel.)
[edit]Maintenance hazards
Fuel injection introduces potential hazards in engine maintenance due to the high fuel
pressures used. Residual pressure can remain in the fuel lines long after an injection-
equipped engine has been shut down. This residual pressure must be relieved, and if
it is done so by external bleed-off, the fuel must be safely contained. If a high-
pressure diesel fuel injector is removed from its seat and operated in open air, there is
a risk to the operator of injury by hypodermic jet-injection, even with only
100 psi pressure.[55] The first known such injury occurred in 1937 during a diesel
engine maintenance operation.[56]
[edit]Diesel applications
The characteristics of diesel have different advantages for different applications.
[edit]Passenger cars
Diesel engines have long been popular in bigger cars and this is spreading to smaller
cars. Diesel engines tend to be more economical at regular driving speeds and are
much better at city speeds. Their reliability and life-span tend to be better (as
detailed). Some 40% or more of all cars sold in Europe are diesel-powered where
they are considered a low CO2 option. Mercedes-Benz in conjunction with Robert
Bosch GmbH produced diesel-powered passenger cars starting in 1936 and very
large numbers are used all over the world (often as "Grande Taxis" in the Third
World).
[edit]Railroad rolling stock
Diesel engines have eclipsed steam engines as the prime mover on all non-electrified
railroads in the industrialized world. The first diesel locomotives appeared in the early
20th century, and diesel multiple units soon after.
While electric locomotives have now replaced the diesel locomotive almost completely
on passenger traffic in Europe and Asia, diesel is still today very popular for cargo-
hauling freight trains and on tracks where electrification is not feasible.
Most modern diesel locomotives are actually diesel-electric locomotives: the diesel
engine is used to power an electric generator that in turn powers electric traction
engines with no mechanical connection between diesel engine and traction.
[edit]Other transport uses
Larger transport applications (trucks, buses, etc.) also benefit from the diesel's
reliability and high torque output. Diesel displaced paraffin (or tractor vaporising oil,
TVO) in most parts of the world by the end of the 1950s with the U.S. following some
20 years later.
Aircraft
Marine
Motorcycles
In merchant ships and boats, the same advantages apply with the relative safety of
diesel fuel an additional benefit. The German pocket battleships were the largest
diesel warships, but the German torpedo-boats known as E-boats (Schnellboot) of the
Second World War were also diesel craft. Conventional submarines have used them
since before the First World War, relying on the almost total absence of carbon
monoxide in the exhaust. American World War II diesel-electric submarines operated
on two-stroke cycle as opposed to the four-stroke cycle that other navies used.
[edit]Military fuel standardisation
NATO has a single vehicle fuel policy and has selected diesel for this purpose. The
use of a single fuel simplifies wartime logistics. NATO and the United States Marine
Corps have even been developing a diesel military motorcycle based on
a Kawasaki off road motorcycle, with a purpose designed naturally aspirated direct
injection diesel at Cranfield University in England, to be produced in the USA,
because motorcycles were the last remaining gasoline-powered vehicle in their
inventory. Before this, a few civilian motorcycles had been built using adapted
stationary diesel engines, but the weight and cost disadvantages generally
outweighed the efficiency gains.
[edit]Non-transport uses
A 1944 V12 2300 kW power plant undergoing testing & restoration works
Diesel engines are also used to power permanent, portable, and backup generators,
irrigation pumps,[57] corn grinders,[58] and coffee de-pulpers.[59]
[edit]Engine speeds
Within the diesel engine industry, engines are often categorized by their rotational
speeds into three unofficial groups:
High-speed engines,
medium-speed engines, and
slow-speed engines
High- and medium-speed engines are predominantly four-stroke engines; except for
the Detroit Diesel two-stroke range. Medium-speed engines are physically larger than
high-speed engines and can burn lower-grade (slower-burning) fuel than high-speed
engines. Slow-speed engines are predominantly large two-stroke crosshead engines,
hence very different from high- and medium-speed engines. Due to the lower
rotational speed of slow- and medium-speed engines, there is more time for
combustion during the power stroke of the cycle, allowing the use of slower-burning
fuels than high-speed engines.
[edit]High-speed engines
High-speed (approximately 1,000 rpm and greater) engines are used to
power trucks (lorries), buses, tractors, cars, yachts, compressors, pumps and
smallelectrical generators. As of 2008, most high-speed engines have direct injection.
Many modern engines, particularly in on-highway applications, have common
rail direct injection, which is cleaner burning.
[edit]Medium-speed engines
Medium-speed engines are used in large electrical generators, ship propulsion and
mechanical drive applications such as large compressors or pumps. Medium speed
diesel engines operate on either diesel fuel or heavy fuel oil by direct injection in the
same manner as low-speed engines.
Engines used in electrical generators run at approximately 300 to 1000 rpm and are
optimized to run at a set synchronous speed depending on the generation frequency
(50 or 60 hertz) and provide a rapid response to load changes. Typical synchronous
speeds for modern medium-speed engines are 500/514 rpm (50/60 Hz), 600 rpm
(both 50 and 60 Hz), 720/750 rpm, and 900/1000 rpm.
As of 2009, the largest medium-speed engines in current production have outputs up
to approximately 20 MW (27,000 hp). and are supplied by companies like MAN
B&W, Wärtsilä,[60] and Rolls-Royce (who acquired Ulstein Bergen Diesel in 1999).
Most medium-speed engines produced are four-stroke machines, however there are
some two-stroke medium-speed engines such as by EMD (Electro-Motive Diesel),
and the Fairbanks Morse OP (Opposed-piston engine) type.
Typical cylinder bore size for medium-speed engines ranges from 20 cm to 50 cm,
and engine configurations typically are offered ranging from in-line 4-cylinder units to
V-configuration 20-cylinder units. Most larger medium-speed engines are started with
compressed air direct on pistons, using an air distributor, as opposed to a pneumatic
starting motor acting on the flywheel, which tends to be used for smaller engines.
There is no definitive engine size cut-off point for this.
It should also be noted that most major manufacturers of medium-speed engines
make natural gas-fueled versions of their diesel engines, which in fact operate on
the Otto cycle, and require spark ignition, typically provided with a spark plug.[52] There
are also dual (diesel/natural gas/coal gas) fuel versions of medium and low speed
diesel engines using a lean fuel air mixture and a small injection of diesel fuel (so-
called "pilot fuel") for ignition. In case of a gas supply failure or maximum power
demand these engines will instantly switch back to full diesel fuel operation.[52][61][62]
[edit]Low-speed engines
The MAN B&W 5S50MC 5-cylinder, 2-stroke, low-speed marine diesel engine. This particular engine
is found aboard a 29,000 tonne chemical carrier.
Also known as slow-speed, or traditionally oil engines, the largest diesel engines are
primarily used to power ships, although there are a few land-based power generation
units as well. These extremely large two-stroke engines have power outputs up to
approximately 85 MW (114,000 hp), operate in the range from approximately 60 to
200 rpm and are up to 15 m (50 ft) tall, and can weigh over 2,000 short tons (1,800 t).
They typically use direct injection running on cheap low-grade heavy fuel, also known
as Bunker C fuel, which requires heating in the ship for tanking and before injection
due to the fuel's high viscosity. The heat for fuel heating is often provided by waste
heat recovery boilers located in the exhaust ducting of the engine, which produce the
steam required for fuel heating. Provided the heavy fuel system is kept warm and
circulating, engines can be started and stopped on heavy fuel.
Large and medium marine engines are started with compressed air directly applied to
the pistons. Air is applied to cylinders to start the engine forwards or backwards
because they are normally directly connected to the propeller without clutch or
gearbox, and to provide reverse propulsion either the engine must be run backwards
or the ship will utilise an adjustable propeller. At least three cylinders are required
with two-stroke engines and at least six cylinders withfour-stroke engines to
provide torque every 120 degrees.
Companies such as MAN B&W Diesel, (formerly Burmeister & Wain)
and Wärtsilä (which acquired Sulzer Diesel) design such large low-speed engines.
They are unusually narrow and tall due to the addition of a crosshead bearing. As of
2007, the 14-cylinder Wärtsilä-Sulzer 14RTFLEX96-C turbocharged two-stroke diesel
engine built by Wärtsilä licensee Doosan in Korea is the most powerful diesel engine
put into service, with a cylinder bore of 960 mm (37.8 in) delivering 114,800 hp
(85.6 MW). It was put into service in September 2006, aboard the world's largest
container ship Emma Maersk which belongs to the A.P. Moller-Maersk Group. Typical
bore size for low-speed engines ranges from approximately 35 to 98 cm (14 to 39 in).
As of 2008, all produced low-speed engines with crosshead bearings are in-line
configurations; no Vee versions have been produced.
[edit]Supercharging and turbocharging
Most diesels are now turbocharged and some are both turbo charged
and supercharged. Because diesels do not have fuel in the cylinder before
combustion is initiated, more than one bar (100 kPa) of air can be loaded in the
cylinder without preignition. A turbocharged engine can produce significantly more
power than a naturally aspirated engine of the same configuration, as having more air
in the cylinders allows more fuel to be burned and thus more power to be produced. A
supercharger is powered mechanically by the engine's crankshaft, while a
turbocharger is powered by the engine exhaust, not requiring any mechanical power.
Turbocharging can improve the fuel economy[63] of diesel engines by recovering waste
heat from the exhaust, increasing the excess air factor, and increasing the ratio of
engine output to friction losses.
A two-stroke engine does not have a discrete exhaust and intake stroke and thus is
incapable of self-aspiration. Therefore all two-stroke engines must be fitted with a
blower to charge the cylinders with air and assist in dispersing exhaust gases, a
process referred to as scavenging. In some cases, the engine may also be fitted with
a turbocharger, whose output is directed into the blower inlet. A few designs employ a
hybrid turbocharger for scavenging and charging the cylinders, which device is
mechanically driven at cranking and low speeds to act as a blower.
As turbocharged or supercharged engines produce more power for a given engine
size as compared to naturally aspirated engines, attention must be paid to the
mechanical design of components, lubrication, and cooling to handle the power.
Pistons are usually cooled with lubrication oil sprayed on the bottom of the piston.
Large engines may use water, sea water, or oil supplied throughtelescoping pipes
attached to the crosshead.
[edit]Current and future developments
See also: Diesel car history
As of 2008, many common rail and unit injection systems already employ new
injectors using stacked piezoelectric wafers in lieu of a solenoid, giving finer control of
the injection event.[64]
Variable geometry turbochargers have flexible vanes, which move and let more air
into the engine depending on load. This technology increases both performance and
fuel economy. Boost lag is reduced as turbo impeller inertia is compensated for.[65]
Accelerometer pilot control (APC) uses an accelerometer to provide feedback on the
engine's level of noise and vibration and thus instruct the ECU to inject the minimum
amount of fuel that will produce quiet combustion and still provide the required power
(especially while idling).[66]
The next generation of common rail diesels is expected to use variable injection
geometry, which allows the amount of fuel injected to be varied over a wider range,
and variable valve timing (see Mitsubishi's 4N13 diesel engine) similar to that
on petrol engines. Particularly in the United States, coming tougher emissions
regulations present a considerable challenge to diesel engine manufacturers.
Ford's HyTrans Project has developed a system which starts the ignition in 400 ms,
saving a significant amount of fuel on city routes, and there are other methods to
achieve even more efficient combustion, such as homogeneous charge compression
ignition, being studied.[67][68]
Lead–acid batteryFrom Wikipedia, the free encyclopedia
Lead–acid battery
lead acid car battery
specific energy 30–40 Wh/kg
energy density 60–75 Wh/l
specific power 180 W/kg
Charge/discharge efficiency 50%–92% [3]
Energy/consumer-price 7(sld)-18(fld) Wh/US$ [4]
Self-discharge rate 3–20%/month [5]
Cycle durability 500–800 cycles
Nominal cell voltage 2.105 V
Lead–acid batteries, invented in 1859 by French physicist Gaston Planté, are the oldest type of rechargeable
battery. Despite having a very low energy-to-weight ratio and a low energy-to-volume ratio, their ability to supply
high surge currents means that the cells maintain a relatively large power-to-weight ratio. These features, along with
their low cost, make them attractive for use in motor vehicles to provide the high current required by automobile
starter motors.
Lead–acid batteries (under 5 kg) account for 1.5% of all portable secondary battery sales in Japan by number of units
sold (25% by price).[1]Sealed lead–acid batteries accounted for 10% by weight of all portable battery sales in the EU in
2000. [2]
Electrochemistry
In the charged state, each cell contains negative electrodes of elemental lead (Pb)
and positive electrodes of lead(IV) oxide (PbO2) in an electrolyte of approximately
33.5% v/v (4.2 Molar) sulfuric acid(H2SO4).
In the discharged state both the positive and negative become lead(II) sulfate (PbSO4)
and the electrolyte loses much of its dissolved sulfuric acid and becomes primarily
water. Due to the freezing-point depression of water, as the battery discharges and
the concentration of sulfuric acid decreases, the electrolyte is more likely to freeze
during winter weather.
[edit]Discharge
Fully Discharged: Two identical lead sulfate plates
During discharge, both plates return to lead sulfate. The process is driven by the
conduction of electrons from the positive plate back into the cell at the negative plate.
Negative Plate Reaction: Pb(s) + HSO−
4(aq) → PbSO4(s) + 2e−
Positive Plate Reaction: PbO2(s) + HSO−
4(aq) + 4H+(aq) + 2e− → PbSO4(s) + 2H2O(l)
[edit]Recharging
Fully Charged: Lead and Lead Oxide plates
Subsequent charging places the battery back in its charged state, changing the
lead sulfates into lead and lead oxides. The process is driven by the forcible
removal of electrons from the negative plate and the forcible introduction of
them to the positive plate.
Negative Plate Reaction: PbSO4(s) + H+(aq) + 2e− → Pb(s) + HSO−
4(aq)Positive Plate Reaction: PbSO4(s) + 2H2O(l) → PbO2(s) + HSO−
4(aq) + 3H+(aq) + 2e−
Overcharging with high
charging voltages generates oxygen and hydrogen gas by electrolysis of
water, which is lost to the cell. Periodic maintenance of lead acid
batteries requires inspection of the electrolyte level and replacement of
any water that has been lost.
[edit]Voltages for common usages
These are general voltage ranges for six-cell lead-acid batteries:
Open-circuit (quiescent) at full charge: 12.6 V to 12.8 V (2.10–2.13V
per cell)
Open-circuit at full discharge: 11.8 V to 12.0 V
Loaded at full discharge: 10.5 V.
Continuous-preservation (float) charging: 13.4 V for gelled electrolyte;
13.5 V for AGM (absorbed glass mat) and 13.8 V for flooded cells
1. All voltages are at 20 °C (68 °F), and must be adjusted
−0.022V/°C for temperature changes.
2. Float voltage recommendations vary, according to the
manufacturer's recommendation.
3. Precise float voltage (±0.05 V) is critical to longevity; insufficient
voltage (causes sulfation) which is almost as detrimental as
excessive voltage (causing corrosion and electrolyte loss)
Typical (daily) charging: 14.2 V to 14.5 V (depending on temperature
and manufacturer's recommendation)
Equalization charging (for flooded lead acids): 15 V for no more than
2 hours. Battery temperature must be monitored.
Gassing threshold: 14.4 V
After full charge, terminal voltage drops quickly to 13.2 V and then
slowly to 12.6 V.
Portable batteries, such as for miners' cap lamps (headlamps) typically
have two cells, and use one third of these voltages.[3]
[edit]Measuring the charge level
A hydrometer can be used to test the specific gravity of each cell as a measure of its
state of charge.
Because the electrolyte takes part in the charge-discharge reaction, this
battery has one major advantage over other chemistries. It is relatively
simple to determine the state of charge by merely measuring the specific
gravity (S.G.) of the electrolyte, the S.G. falling as the battery
discharges. Some battery designs include a simple hydrometer using
colored floating balls of differing density. When used in diesel-
electric submarines, the S.G. was regularly measured and written on a
blackboard in the control room to indicate how much longer the boat
could remain submerged.[4]
A battery's open-circuit voltage can be used to estimate the state of charge, in this
case for a 12-volt battery.[5]
[edit]Construction
[edit]Plates
The lead–acid cell can be demonstrated using sheet lead plates for the
two electrodes. However such a construction produces only around one
ampere for roughly postcard sized plates, and for only a few minutes.
Gaston Planté found a way to provide a much larger effective surface
area. In Planté's design, the positive and negative plates were formed of
two spirals of lead foil, separated with a sheet of cloth and coiled up. The
cells initially had low capacity, so a slow process of "forming" was
required to corrode the lead foils, creating lead dioxide on the plates and
roughening them to increase surface area. Initially this process used
electricity from primary batteries; when generators became available
after 1870, the cost of production of batteries greatly declined.[6] Planté
plates are still used in some stationary applications, where the plates are
mechanically grooved to increase their surface area.
Faure pasted-plate construction is typical of automotive batteries. Each
plate consists of a rectangular lead grid alloyed with antimony or calcium
to improve the mechanical characteristics. The holes of the grid are filled
with a paste of red lead and 33% dilute sulfuric acid. (Different
manufacturers vary the mixture). The paste is pressed into the holes in
the grid which are slightly tapered on both sides to better retain the
paste. This porous paste allows the acid to react with the lead inside the
plate, increasing the surface area many fold. Once dry, the plates are
stacked with suitable separators and inserted in the battery container. An
odd number of plates is usually used, with one more nagative plate than
positive. Each alternate plate is connected.
The positive plates are the chocolate brown color of Lead(IV) Oxide, and
the negative are the slate gray of "spongy" lead at the time of
manufacture. In this charged state the plates are called 'formed'.
One of the problems with the plates is that the plates increase in size as
the active material absorbs sulfate from the acid during discharge, and
decrease as they give up the sulfate during charging. This causes the
plates to gradually shed the paste. It is important that there is room
underneath the plates to catch this shed material. If it reaches the plates,
the cell short-circuits.
The paste contains carbon black, blanc fixe (barium sulfate)
and lignosulfonate. The blanc fixe acts as a seed crystal for the lead–to–
lead sulfate reaction. The blanc fixe must be fully dispersed in the paste
in order for it to be effective. The lignosulfonate prevents the negative
plate from forming a solid mass during the discharge cycle, instead
enabling the formation of long needle–like crystals. The long crystals
have more surface area and are easily converted back to the original
state on charging. Carbon black counteracts the effect of inhibiting
formation caused by the lignosulfonates.
Sulfonated naphthalene condensate dispersant is a more effective
expander than lignosulfonate and speeds up formation. This dispersant
improves dispersion of barium sulfate in the paste, reduces hydroset
time, produces a more breakage-resistant plate, reduces fine lead
particles and thereby improves handling and pasting characteristics. It
extends battery life by increasing end–of–charge voltage. Sulfonated
naphthalene requires about one-third to one-half the amount of
lignosulfonate and is stable to higher temperatures.[7]
Practical cells are usually not made with pure lead but have small
amounts of antimony, tin, calcium or selenium alloyed in the plate
material to add strength and simplify manufacture. The alloying element
has a great effect on the life of the batteries, with calcium-alloyed plates
preferred over antimony for longer life and less water consumption on
each charge/discharge cycle.
About 60% of the weight of an automotive-type lead–acid battery rated
around 60 Ah (8.7 kg of a 14.5 kg battery) is lead or internal parts made
of lead; the balance is electrolyte, separators, and the case.[6]
[edit]Separators
Separators between the positive and negative plates prevent short-
circuit through physical contact, mostly through dendrites (‘treeing’), but
also through shedding of the active material. Separators obstruct the
flow of ions between the plates and increase the internal resistance of
the cell. Wood, rubber, glass fiber mat, cellulose,
and PVC or polyethylene plastic have been used to make separators.
Wood was the original choice, but deteriorated in the acid electrolyte.
Rubber separators were stable in the battery acid.
An effective separator must possess a number of mechanical properties;
such as permeability, porosity, pore size distribution, specific surface
area, mechanical design and strength, electrical resistance, ionic
conductivity, and chemical compatibility with the electrolyte. In service,
the separator must have good resistance to acid and oxidation. The area
of the separator must be a little larger than the area of the plates to
prevent material shorting between the plates. The separators must
remain stable over the battery's operating temperature range.
[edit]Applications
Most of the world's lead–acid batteries are automobile starting, lighting
and ignition (SLI) batteries, with an estimated 320 million units shipped
in 1999.[6] In 1992 about 3 million tons of lead were used in the
manufacture of batteries.
Wet cell stand-by (stationary) batteries designed for deep discharge are
commonly used in large backup power supplies for telephone and
computer centers, grid energy storage, and off-grid household electric
power systems.[8] Lead–acid batteries are used in emergency lighting in
case of power failure.
Traction (propulsion) batteries are used for in golf carts and other battery
electric vehicles. Large lead–acid batteries are also used to power
the electric motors in diesel-electric (conventional)submarines and are
used on nuclear submarines as well. Valve-regulated lead acid
batteries cannot spill their electrolyte. They are used in back-up
power supplies for alarm and smaller computer systems (particularly in
uninterruptible power supplies) and for electric scooters,
electric wheelchairs, electrified bicycles, marine applications, battery
electric vehicles or micro hybrid vehicles, and motorcycles.
Lead–acid batteries were used to supply the filament (heater) voltage,
with 2 V common in early vacuum tube (valve) radio receivers.
[edit]Cycles
[edit]Starting batteriesMain article: Car battery
Lead acid batteries designed for starting automotive engines are not
designed for deep discharge. They have a large number of thin plates
designed for maximum surface area, and therefore maximum current
output, but which can easily be damaged by deep discharge. Repeated
deep discharges will result in capacity loss and ultimately in premature
failure, as the electrodes disintegrate due tomechanical stresses that
arise from cycling. Starting batteries kept on continuous float charge will
have corrosion in the electrodes and result in premature failure. Starting
batteries should be kept open circuit but charged regularly (at least once
every two weeks) to prevent sulfation.
Starting batteries are lighter weight than deep cycle batteries of the
same battery dimensions, because the cell plates do not extend all the
way to the bottom of the battery case. This allows loose disintegrated
lead to fall off the plates and collect under the cells, to prolong the
service life of the battery. If this loose debris rises high enough it can
touch the plates and lead to failure of a cell, resulting in loss of battery
voltage and capacity.
[edit]Deep cycle batteriesMain article: Deep cycle battery
Specially designed deep-cycle cells are much less susceptible to
degradation due to cycling, and are required for applications where the
batteries are regularly discharged, such as photovoltaicsystems, electric
vehicles (forklift, golf cart, electric cars and other) and uninterruptible
power supplies. These batteries have thicker plates that can deliver
less peak current, but can withstand frequent discharging.[9]
Some batteries are designed as a compromise between starter (high-
current) and deep cycle batteries. They are able to be discharged to a
greater degree than automotive batteries, but less so than deep cycle
batteries. They may be referred to as "Marine/Motorhome" batteries, or
"leisure batteries".
[edit]Fast and slow charge and discharge
Charge current needs to match the ability of the battery to absorb the energy. Using
too large of a charge current on a small battery can lead to boiling and venting of the
electrolyte. In this image a VRLA battery case has ballooned due to the high gas
pressure developed during overcharge.
The capacity of a lead–acid battery is not a fixed quantity but varies
according to how quickly it is discharged. An empirical relationship exists
between discharge rate and capacity, known as Peukert's law.
When a battery is charged or discharged, this initially affects only the
reacting chemicals, which are at the interface between the electrodes
and the electrolyte. With time, the charge stored in the chemicals at the
interface, often called "interface charge", spreads by diffusion of these
chemicals throughout the volume of the active material.
If a battery has been completely discharged (e.g. the car lights were left
on overnight) and next is given a fast charge for only a few minutes, then
during the short charging time it develops only a charge near the
interface. The battery voltage may rise to be close to the charger voltage
so that the charging current decreases significantly. After a few hours
this interface charge will spread to the volume of the electrode and
electrolyte, leading to an interface charge so low that it may be
insufficient to start the car.[10]
On the other hand, if the battery is given a slow charge, which takes
longer, then the battery will become more fully charged. During a slow
charge the interface charge has time to redistribute to the volume of the
electrodes and electrolyte, while being replenished by the charger. The
battery voltage remains below the charger voltage throughout this
process allowing charge to flow into the battery.
Similarly, if a battery is subject to a fast discharge (such as starting a
car, a current draw of more than 100 amps) for a few minutes, it will
appear to go dead, exhibiting reduced voltage and power. However, it
may have only lost its interface charge. If the discharge is halted for a
few minutes the battery may resume normal operation at the appropriate
voltage and power for its state of discharge. On the other hand, if a
battery is subject to a slow, deep discharge (such as leaving the car
lights on, a current draw of less than 7 amps) for hours, then any
observed reduction in battery performance is likely permanent.
[edit]Valve regulated
In a valve regulated lead acid (VRLA) battery the hydrogen and oxygen
produced in the cells largely recombine into water. Leakage is minimal,
although some electrolyte still escapes if the recombination cannot keep
up with gas evolution. Since VRLA batteries do not require (and make
impossible) regular checking of the electrolyte level, they have been
called maintenance free batteries. However, this is somewhat of a
misnomer. VRLA cells do require maintenance. As electrolyte is lost,
VRLA cells "dry-out" and lose capacity. This can be detected by taking
regular internal resistance,conductance or impedance measurements.
Regular testing reveals whether more involved testing and maintenance
is required. Recent maintenance procedures have been developed
allowing "rehydration", often restoring significant amounts of lost
capacity.
VRLA types became popular on motorcycles around 1983,[11] because
the acid electrolyte is absorbed into the separator, so it cannot spill.[12] The separator also helps them better withstand vibration. They are
also popular in stationary applications such as telecommunications sites,
due to their small footprint and installation flexibility.[13]
The electrical characteristics of VRLA batteries differ somewhat from
wet-cell lead–acid batteries, requiring caution in charging and
discharging.
[edit]Sulfation
Lead–acid batteries lose the ability to accept a charge when discharged
for too long due to sulfation, the crystallization of lead sulfate. They
generate electricity through a double sulfate chemical reaction. Lead
and Lead(IV) Oxide, which are the active materials on the battery's
plates, react with sulfuric acid in the electrolyte to form lead sulfate. The
lead sulfate first forms in a finely divided,amorphous state, and easily
reverts to lead, lead oxide and sulfuric acid when the battery recharges.
As batteries cycle through numerous discharge and charges, the lead
sulfate slowly converts to a stable crystalline form that no longer
dissolves on recharging. Thus, not all the lead is returned to the battery
plates, and the amount of usable active material necessary for electricity
generation declines over time.
Sulfation occurs in all lead–acid batteries during normal operation. It
clogs the grids, impedes recharging and ultimately expands, cracking the
plates and destroying the battery. In addition, the sulfate portion (of the
lead sulfate) is not returned to the electrolyte as sulfuric acid. The large
crystals physically block the electrolyte from entering the pores of the
plates. Sulfation can be avoided if the battery is fully recharged
immediately after a discharge cycle.[14]
Sulfation also affects the charging cycle, resulting in longer charging
times, less efficient and incomplete charging, and higher battery
temperatures.
The process can often be at least partially prevented and/or reversed by
a desulfation technique called pulse conditioning, in which short but
powerful current surges are repeatedly sent through the damaged
battery. Over time, this procedure tends to break down and dissolve the
sulfate crystals, restoring some capacity.[15]
Higher temperature speeds both desulfation and sulfation, although too
much heat damages the battery by accelerating corrosion.
[edit]Stratification
A typical lead–acid battery contains a mixture with varying
concentrations of water and acid. There is a slight difference in density
between water and acid, and if the battery is allowed to sit idle for long
periods of time, the mixture can separate into distinct layers with the
water rising to the top and the acid sinking to the bottom. This results in
a difference of acid concentration across the surface of the plates, and
can lead to greater corrosion of the bottom half of the plates.[6]
Frequent charging and discharging tends to stir up the mixture, since
the electrolysis of water during charging forms hydrogen and oxygen
bubbles that rise and displace the liquid as the bubbles move upward.
Batteries in moving vehicles are also subject to sloshing and splashing in
the cells, as the vehicle accelerates, brakes, and turns.
[edit]Risk of explosion
Car battery after explosion
Excessive charging electrolyzes some of the water emitting hydrogen
and oxygen. This process is known as "gassing". Wet cells have open
vents to release any gas produced, and VRLA batteries rely on valves
fitted to each cell. Wet cells come with catalytic caps to recombine any
emitted hydrogen. A VRLA cell normally recombines
any hydrogen and oxygen produced inside the cell, but malfunction or
overheating may cause gas to build up. If this happens (e.g., by
overcharging) the valve vents the gas and normalizes the pressure,
producing a characteristic acid smell. Valves can sometimes fail
however, if dirt and debris accumulate, allowing pressure to build up.
If the accumulated hydrogen and oxygen within either a VRLA or wet cell
is ignited, an explosion results. The force can burst the plastic casing or
blow the top off the battery, spraying acid and casing shrapnel. An
explosion in one cell may ignite the combustible gas mixture in
remaining cells.
The cell walls of VRLA batteries typically swell when the internal
pressure rises. The deformation varies from cell to cell, and is greater at
the ends where the walls are unsupported by other cells. Such over-
pressurized batteries should be carefully isolated and discarded.
Personnel working near batteries at risk for explosion should protect
their eyes and exposed skin from burns due to spraying acid and fire by
wearing a face shield, overalls, and gloves. Using goggles instead of
a face shield sacrifices safety by leaving one's face exposed to acid and
heat from a potential explosion.
[edit]Environment
[edit]Environmental concerns
According to a 2003 report entitled, "Getting the Lead Out,"
by Environmental Defense and the Ecology Center of Ann Arbor, Mich.,
the batteries of vehicles on the road contained an estimated 2,600,000
metric tons (2,600,000 long tons; 2,900,000 short tons) of lead. Some
lead compounds are extremely toxic. Long-term exposure to even tiny
amounts of these compounds can cause brain and kidney damage,
hearing impairment, and learning problems in children.[16] The auto
industry uses over 1,000,000 metric tons (980,000 long tons; 1,100,000
short tons) every year, with 90% going to conventional lead-acid vehicle
batteries. While lead recycling is a well-established industry, more than
40,000 metric tons (39,000 long tons; 44,000 short tons) ends up in
landfills every year. According to the federal Toxic Release Inventory,
another 70,000 metric tons (69,000 long tons; 77,000 short tons) are
released in the lead mining and manufacturing process.[17]
Attempts are being made to develop alternatives (particularly for
automotive use) because of concerns about the environmental
consequences of improper disposal and of lead smelting operations,
among other reasons. Alternatives are unlikely to displace them for
applications such as engine starting or backup power systems, since the
batteries are low-cost although heavy.
[edit]RecyclingSee also: Automotive battery recycling
Lead–acid battery recycling is one of the most successful recycling
programs in the world. In the United States 97% of all battery lead was
recycled between 1997 and 2001.[18] An effective pollution control system
is a necessity to prevent lead emission. Continuous improvement in
battery recycling plants and furnace designs is required to keep pace
with emission standards for lead smelters.
[edit]Additives
Since the 1950s chemical additives have been used to reduce lead
sulfate build up on plates and improve battery condition when added to
the electrolyte of a vented lead–acid battery. Such treatments are rarely,
if ever, effective.[19]
Two compounds used for such purposes are Epsom salts and EDTA.
Epsom salts reduces the internal resistance in a weak or damaged
battery and may allow a small amount of extended life. EDTA can be
used to dissolve the sulfate deposits of heavily discharged plates.
However, the dissolved material is then no longer available to participate
in the normal charge/discharge cycle, so a battery temporarily revived
with EDTA will have a reduced life expectancy. Residual EDTA in the
lead–acid cell forms organic acids which will accelerate corrosion of the
lead plates and internal connectors.
The active materials change physical form during charge/discharge,
resulting in growth and distortion of the electrodes, and shedding of
electrode into the electrolyte. Once the active material has fallen out of
the plates, it cannot be restored into position by any chemical treatment.
Similarly, internal physical problems such as cracked plates, corroded
connectors, or damaged separators cannot be restored chemically.
[edit]Corrosion problems
Corrosion of the external metal parts of the lead–acid battery results
from a chemical reaction of the battery terminals, lugs and connectors.
Corrosion on the positive terminal is caused by electrolysis, due a
mismatch of metal alloys used in the manufacture of the battery terminal
and cable connector. White corrosion is usually lead or zinc
sulfate crystals. Aluminum connectors corrode to aluminum sulfate.
Copper connectors produce blue and white corrosion crystals. Corrosion
of a battery's terminals can be reduced by coating the terminals with
petroleum jelly[citation needed] or a commercially available product made for
the purpose.
If the battery is over-filled with water and electrolyte, thermal expansion
can force some of the liquid out of the battery vents onto the top of the
battery. This solution can then react with the lead and other metals in the
battery connector and cause corrosion.
The electrolyte can weep from the plastic-to-lead seal where the battery
terminals penetrate the plastic case.
Acid fumes that vaporize through the vent caps, often caused by
overcharging, and insufficient battery box ventilation can allow the
sulfuric acid fumes to build up and react with the exposed metals.
Electric Generator
In electricity generation, an electric generator is a device that converts mechanical
energy to electrical energy. A generator forces electric charge (usually carried
by electrons) to flow through an external electrical circuit. It is analogous to a water
pump, which causes water to flow (but does not create water). The source of
mechanical energy may be a reciprocating or turbine steam engine, water falling
through a turbine or waterwheel, an internal combustion engine, a wind turbine, a
handcrank, compressed air or any other source of mechanical energy.
Early 20th century alternator made inBudapest, Hungary, in the power generating hall of
a hydroelectric station
Early Ganz Generator in Zwevegem,West Flanders, Belgium
The reverse conversion of electrical energy into mechanical energy is done by
an electric motor, and motors and generators have many similarities. In fact many
motors can be mechanically driven to generate electricity, and very frequently make
acceptable generators.
DynamoMain article: Dynamo
Dynamos are no longer used for power generation due to the size and complexity of the commutator
needed for high power applications. This large belt-driven high-current dynamo produced 310
amperes at 7 volts, or 2,170 watts, when spinning at 1400 RPM.
Dynamo Electric Machine [End View, Partly Section] (U.S. Patent 284,110)
The dynamo was the first electrical generator capable of delivering power for
industry. The dynamo uses electromagnetic principles to convert mechanical rotation
into pulsed DC through the use of acommutator. The first dynamo was built
by Hippolyte Pixii in 1832.
Through a series of accidental discoveries, the dynamo became the source of many
later inventions, including the DC electric motor, the AC alternator, the
AC synchronous motor, and the rotary converter.
A dynamo machine consists of a stationary structure, which provides a constant
magnetic field, and a set of rotating windings which turn within that field. On small
machines the constant magnetic field may be provided by one or more permanent
magnets; larger machines have the constant magnetic field provided by one or more
electromagnets, which are usually called field coils.
Large power generation dynamos are now rarely seen due to the now nearly universal
use of alternating current for power distribution and solid state electronic AC to DC
power conversion. But before the principles of AC were discovered, very large direct-
current dynamos were the only means of power generation and distribution. Now
power generation dynamos are mostly a curiosity.
[edit]Alternator
Without a commutator, a dynamo becomes an alternator, which is a synchronous
singly fed generator. When used to feed an electric power grid, an alternator must
always operate at a constant speed that is precisely synchronized to the electrical
frequency of the power grid. A DC generator can operate at any speed within
mechanical limits, but always outputs direct current.
Typical alternators use a rotating field winding excited with direct current, and a
stationary (stator) winding that produces alternating current. Since the rotor field only
requires a tiny fraction of the power generated by the machine, the brushes for the
field contact can be relatively small. In the case of a brushless exciter, no brushes are
used at all and the rotor shaft carries rectifiers to excite the main field winding.
[edit]Other rotating electromagnetic generators
Other types of generators, such as the asynchronous or induction singly fed
generator, the doubly fed generator, or the brushless wound-rotor doubly fed
generator, do not incorporate permanent magnets or field windings (i.e.,
electromagnets) that establish a constant magnetic field, and as a result, are seeing
success in variable speed constant frequency applications, such as wind turbines or
other renewable energy technologies.
The full output performance of any generator can be optimized with electronic control
but only the doubly fed generators or the brushless wound-rotor doubly fed
generator incorporate electronic control with power ratings that are substantially less
than the power output of the generator under control, a feature which, by itself, offers
cost, reliability and efficiency benefits.
[edit]MHD generatorMain article: MHD generator
A magnetohydrodynamic generator directly extracts electric power from moving hot
gases through a magnetic field, without the use of rotating electromagnetic machinery.
MHD generators were originally developed because the output of a plasma MHD
generator is a flame, well able to heat the boilers of a steam power plant. The first
practical design was the AVCO Mk. 25, developed in 1965. The U.S. government
funded substantial development, culminating in a 25 MW demonstration plant in 1987.
In the Soviet Union from 1972 until the late 1980s, the MHD plant U 25 was in regular
commercial operation on the Moscow power system with a rating of 25 MW, the
largest MHD plant rating in the world at that time.[2] MHD generators operated as
a topping cycle are currently (2007) less efficient than combined-cycle gas turbines.
[edit]Terminology
The two main parts of a generator or motor can be described in either mechanical or
electrical terms.
Mechanical:
Rotor : The rotating part of an electrical machine
Stator : The stationary part of an electrical machine
Electrical:
Armature : The power-producing component of an electrical machine. In a
generator, alternator, or dynamo the armature windings generate the electric
current. The armature can be on either the rotor or the stator.
Field : The magnetic field component of an electrical machine. The magnetic
field of the dynamo or alternator can be provided by either electromagnets or
permanent magnets mounted on either the rotor or the stator.
Because power transferred into the field circuit is much less than in the armature
circuit, AC generators nearly always have the field winding on the rotor and the stator
as the armature winding. Only a small amount of field current must be transferred to
the moving rotor, using slip rings. Direct current machines (dynamos) require
a commutator on the rotating shaft to convert the alternating currentproduced by the
armature to direct current, so the armature winding is on the rotor of the machine.
[edit]Excitation
A small early 1900s 75 KVA direct-driven power station AC alternator, with a separate belt-driven
exciter generator.
Main article: Excitation (magnetic)
An electric generator or electric motor that uses field coils rather than permanent
magnets requires a current to be present in the field coils for the device to be able to
work. If the field coils are not powered, the rotor in a generator can spin without
producing any usable electrical energy, while the rotor of a motor may not spin at all.
Smaller generators are sometimes self-excited, which means the field coils are
powered by the current produced by the generator itself. The field coils are connected
in series or parallel with the armature winding. When the generator first starts to turn,
the small amount of remanent magnetism present in the iron core provides a magnetic
field to get it started, generating a small current in the armature. This flows through
the field coils, creating a larger magnetic field which generates a larger armature
current. This "bootstrap" process continues until the magnetic field in the core levels
off due to saturation and the generator reaches a steady state power output.
Very large power station generators often utilize a separate smaller generator to
excite the field coils of the larger. In the event of a severe widespread power
outage where islanding of power stations has occurred, the stations may need to
perform ablack start to excite the fields of their largest generators, in order to restore
customer power service.[3]
[edit]Equivalent circuit
Equivalent circuit of generator and load.
G = generator
VG=generator open-circuit voltage
RG=generator internal resistance
VL=generator on-load voltage
RL=load resistance
The equivalent circuit of a generator and load is shown in the diagram to the right. The
generator's VG and RG parameters can be determined by measuring the winding
resistance (corrected to operating temperature), and measuring the open-circuit and
loaded voltage for a defined current load.
[edit]Vehicle-mounted generators
Early motor vehicles until about the 1960s tended to use DC generators with
electromechanical regulators. These have now been replaced by alternators with built-
in rectifier circuits, which are less costly and lighter for equivalent output. Moreover,
the power output of a DC generator is proportional to rotational speed, whereas the
power output of an alternator is independent of rotational speed. As a result, the
charging output of an alternator at engine idle speed can be much greater than that of
a DC generator. Automotive alternators power the electrical systems on the vehicle
and recharge the battery after starting. Rated output will typically be in the range 50-
100 A at 12 V, depending on the designed electrical load within the vehicle. Some
cars now have electrically poweredsteering assistance and air conditioning, which
places a high load on the electrical system. Large commercial vehicles are more likely
to use 24 V to give sufficient power at the starter motor to turn over a large diesel
engine. Vehicle alternators do not use permanent magnets and are typically only 50-
60% efficient over a wide speed range.[4] Motorcycle alternators often use permanent
magnet stators made with rare earth magnets, since they can be made smaller and
lighter than other types. See also hybrid vehicle.
Some of the smallest generators commonly found power bicycle lights. These tend to
be 0.5 ampere, permanent-magnet alternators supplying 3-6 W at 6 V or 12 V. Being
powered by the rider, efficiency is at a premium, so these may incorporate rare-earth
magnets and are designed and manufactured with great precision. Nevertheless, the
maximum efficiency is only around 80% for the best of these generators—60% is
more typical—due in part to the rolling friction at the tyre–generator interface from
poor alignment, the small size of the generator, bearing losses and cheap design. The
use of permanent magnets means that efficiency falls even further at high speeds
because the magnetic field strength cannot be controlled in any way. Hub generators
remedy many of these flaws since they are internal to the bicycle hub and do not
require an interface between the generator and tyre. Until recently, these generators
have been expensive and hard to find. Major bicycle component manufacturers like
Shimano and SRAM have only just entered this market. However, significant gains
can be expected in future as cycling becomes more mainstream transportation and
LED technology allows brighter lighting at the reduced current these generators are
capable of providing.
Sailing yachts may use a water or wind powered generator to trickle-charge the
batteries. A small propeller, wind turbine or impeller is connected to a low-power
alternator and rectifier to supply currents of up to 12 A at typical cruising speeds.
[edit]Engine-generator
Main article: Engine-generator
An engine-generator is the combination of an electrical generator and
an engine (prime mover) mounted together to form a single piece of self-contained
equipment. The engines used are usually piston engines, but gas turbines can also be
used. Many different versions are available - ranging from very small
portable petrol powered sets to large turbine installations.
[edit]Human powered electrical generators
Main article: Self-powered equipment
Protesters at Occupy Wall Street using bicycles connected to a motor and one-way diode to charge
batteries for their electronics[5]
A generator can also be driven by human muscle power (for instance, in field radio
station equipment).
Human powered direct current generators are commercially available, and have been
the project of some DIY enthusiasts. Typically operated by means of pedal power, a
converted bicycle trainer, or a foot pump, such generators can be practically used to
charge batteries, and in some cases are designed with an integral inverter. The
average adult could generate about 125-200 watts on a pedal powered generator, but
at a power of 200 W, a typical healthy human will reach complete exhaustion and fail
to produce any more power after approximately 1.3 hours.[6] Portable radio receivers
with a crank are made to reduce battery purchase requirements, see clockwork radio.
During the mid 20th century, pedal powered radios were used throughout the
Australian outback, to provide schooling,(school of the air) medical and other needs in
remote stations and towns.
[edit]Linear electric generator
In the simplest form of linear electric generator, a sliding magnet moves back and
forth through a solenoid - a spool of copper wire. An alternating current is induced in
the loops of wire by Faraday's law of induction each time the magnet slides through.
This type of generator is used in the Faraday flashlight. Larger linear electricity
generators are used in wave power schemes.
[edit]Tachogenerator
Tachogenerators are frequently used to power tachometers to measure the speeds of
electric motors, engines, and the equipment they power. Generators generate voltage
roughly proportional to shaft speed. With precise construction and design, generators
can be built to produce very precise voltages for certain ranges of shaft speeds
Starter motorFrom Wikipedia, the free encyclopedia
This article is about engine starters. For other kinds of starters, see Starter (disambiguation).
An automobile starter motor
A starter motor (also starting motor or starter) is an electric motor for rotating an internal-combustion engine so as
to initiate the engine's operation under its own power.
Electric starter
1. Main Housing (yoke)
2. Overrunning clutch , and Pinion gear assembly
3. Armature
4. Field coils with Brushes attached
5. Brush-carrier
6. Solenoid
The modern starter motor is either a permanent-magnet or a series-parallel
wound direct current electric motor with a starter solenoid (similar to a relay) mounted
on it. When current from the starting battery is applied to the solenoid, usually through
a key-operated switch, the solenoid engages a lever that pushes out the
drive pinion on the starter driveshaft and meshes the pinion with the starter ring
gear on the flywheel of the engine.
The solenoid also closes high-current contacts for the starter motor, which begins to
turn. Once the engine starts, the key-operated switch is opened, a spring in the
solenoid assembly pulls the pinion gear away from the ring gear, and the starter motor
stops. The starter's pinion is clutched to its driveshaft through an overrunning sprag
clutch which permits the pinion to transmit drive in only one direction. In this manner,
drive is transmitted through the pinion to the flywheel ring gear, but if the pinion
remains engaged (as for example because the operator fails to release the key as
soon as the engine starts, or if there is a short and the solenoid remains engaged),
the pinion will spin independently of its driveshaft. This prevents the engine driving the
starter, for such backdrive would cause the starter to spin so fast as to fly apart.
However, this sprag clutch arrangement would preclude the use of the starter as a
generator if employed in hybrid scheme mentioned above, unless modifications were
made. Also, a standard starter motor is only designed for intermittent use which would
preclude its use as a generator; the electrical components are designed only to
operate for typically under 30 seconds before overheating (by too-slow dissipation of
heat from ohmic losses), to save weight and cost. This is the same reason why most
automobile owner's manuals instruct the operator to pause for at least ten seconds
after each ten or fifteen seconds of cranking the engine, when trying to start an engine
that does not start immediately.
This overrunning-clutch pinion arrangement was phased into use beginning in the
early 1960s; before that time, a Bendix drive was used. The Bendix system places the starter
drive pinion on a helically cut driveshaft. When the starter motor begins turning, the inertia of the
drive pinion assembly causes it to ride forward on the helix and thus engage with the ring gear. When
the engine starts, backdrive from the ring gear causes the drive pinion to exceed the rotative speed of
the starter, at which point the drive pinion is forced back down the helical shaft and thus out of mesh
with the ring gear.
Hear a Folo-Thru starter
A starter motor with Bendix Folo-Thru drive cranks a Chrysler Slant-6 engine. The Folo-Thru drive pinion stays engaged through a cylinder firing but not causing the engine to start
Problems listening to this file? See media help.
An intermediate development between the Bendix drive developed in the 1930s and
the overrunning-clutch designs introduced in the 1960s was the Bendix Folo-Thru
drive. The standard Bendix drive would disengage from the ring gear as soon as the
engine fired, even if it did not continue to run. The Folo-Thru drive contains a latching
mechanism and a set of flyweights in the body of the drive unit. When the starter
motor begins turning and the drive unit is forced forward on the helical shaft by inertia,
it is latched into the engaged position. Only once the drive unit is spun at a speed
higher than that attained by the starter motor itself (i.e., it is backdriven by the running
engine) will the flyweights pull radially outward, releasing the latch and permitting the
overdriven drive unit to be spun out of engagement. In this manner, unwanted starter
disengagement is avoided before a successful engine start.
[edit]Gear reduction
Hear a gear-reduction starter
A Chrysler gear-reduction starter cranks a V8 engine
Problems listening to this file? See media help.
Chrysler Corporation contributed materially to the modern development of the starter
motor. In 1962, Chrysler introduced a starter incorporating ageartrain between the
motor and the driveshaft. Rolls Royce had introduced a conceptually similar starter in
1946,[citation needed] but Chrysler's was the first volume-production unit. The motor shaft
has integrally cut gear teeth forming a pinion which meshes with a larger adjacent
driven gear to provide a gear reduction ratio of 3.75:1. This permits the use of a
higher-speed, lower-current, lighter and more compact motor assembly while
increasing cranking torque.[3] Variants of this starter design were used on most rear-
and four-wheel-drive vehicles produced by Chrysler Corporation from 1962 through
1987. It makes a unique, distinct sound when cranking the engine, which led to it
being nicknamed the "Highland Park Hummingbird"—a reference to Chrysler's
headquarters in Highland Park, Michigan.[4]
The Chrysler gear-reduction starter formed the conceptual basis for the gear-
reduction starters that now predominate in vehicles on the road. Many Japanese
automakers phased in gear reduction starters in the 1970s and 1980s.[citation needed] Light
aircraft engines also made extensive use of this kind of starter, because its light
weight offered an advantage.
Those starters not employing offset geartrains like the Chrysler unit generally employ
planetary epicyclic geartrains instead. Direct-drive starters are almost entirely
obsolete owing to their larger size, heavier weight and higher current requirements.[citation needed]
[edit]Movable pole shoe
Ford also issued a nonstandard starter, a direct-drive "movable pole shoe" design that
provided cost reduction rather than electrical or mechanical benefits. This type of
starter eliminated the solenoid, replacing it with a movable pole shoe and a separate
starter relay. This starter operates as follows: The driver turns the key, activating the
starter switch. A small electric current flows through the switch-type starter solenoid,
closing the contacts and sending large battery current to the starter motor. One of the
pole shoes, hinged at the front, linked to the starter drive, and spring-loaded away
from its normal operating position, is swung into position by the magnetic field created
by electricity flowing through its field coil. This moves the starter drive forward to
engage the flywheel ring gear, and simultaneously closes a pair of contacts supplying
current to the rest of the starter motor winding. Once the engine starts and the driver
releases the starter switch, a spring retracts the pole shoe, which pulls the starter
drive out of engagement with the ring gear.
This starter was used on Ford vehicles from 1973 through 1990, when a gear-
reduction unit conceptually similar to the Chrysler unit replaced it.
[edit]Pneumatic starter
Main article: Air start system
Some gas turbine engines and Diesel engines, particularly on trucks, use
a pneumatic self-starter. The system consists of a geared turbine, an air
compressor and a pressure tank. Compressed air released from the tank is used to
spin the turbine, and through a set of reduction gears, engages the ring gear on the
flywheel, much like an electric starter. The engine, once running, powers the
compressor to recharge the tank.
Aircraft with large gas turbine engines are typically started using a large volume of
low-pressure compressed air, supplied from a very small engine referred to as
an auxiliary power unit, located elsewhere in the aircraft. After starting the main
engines, the APU often continues to operate, supplying additional power to operate
aircraft equipment. Alternately, aircraft engines can be rapidly started using a mobile
ground-based pneumatic starting engine, referred to as a start cart or air start cart.
On larger diesel generators found in large shore installations and especially on ships,
a pneumatic starting gear is used. The air motor is normally powered by compressed
air at pressures of 10–30 bar. The air motor is made up of a center drum about the
size of a soup can with four or more slots cut into it to allow for the vanes to be placed
radially on the drum to form chambers around the drum. The drum is offset inside a
round casing so that the inlet air for starting is admitted at the area where the drum
and vanes form a small chamber compared to the others. The compressed air can
only expand by rotating the drum which allows the small chamber to become larger
and puts another one of the cambers in the air inlet. The air motor spins much too fast
to be used directly on the flywheel of the engine, instead a large gearing reduction
such as a planetary gear is used to lower the output speed. A Bendix gear is used to
engage the flywheel.
On large diesel generators and almost all diesel engines used as the prime mover of
ships will use compressed air acting directly on the cylinder head. This is not ideal for
smaller diesels as it provides too much cooling on starting. Also the cylinder head
needs to have enough space to support an extra valve for the air start system. The air
start system operates very similar to a distributor in a car. There is an air distributor
that is geared to the camshaft of the diesel engine, on the top of the air distributor is a
single lobe similar to what is found on a camshaft. Arranged radially around this lobe
are roller tip followers for every cylinder. When the lobe of the air distributor hits one of
the followers it will send an air signal that acts upon the back of the air start valve
located in the cylinder head causing it to open. The actual compressed air is provided
from a large reservoir that feeds into a header located along the engine. As soon as
the air start valve is opened the compressed air is admitted and the engine will begin
turning. It can be used on 2-cycle and 4-cycle engines and on reversing engines. On
large 2-stroke engines less than one revolution of the crankshaft is needed for
starting.
Since large trucks typically use air brakes, the system does double duty, supplying
compressed air to the brake system. Pneumatic starters have the advantages of
delivering high torque, mechanical simplicity and reliability. They eliminate the need
for oversized, heavy storage batteries in prime mover electrical systems.
[edit]Hydraulic starter
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this section by adding citations to reliable sources. Unsourced material may
be challenged and removed. (December 2010)
Some diesel engines from 6 to 16 cylinders are started by means of a hydraulic motor.
Hydraulic starters and the associated systems provide a sparkless, reliable method of engine starting at
a wide temperature range. Typically hydraulic starters are found in applications such as remote
generators, lifeboat propulsion engines, offshore fire pumping engines, and hydraulic fracturing rigs.
The system used to support the hydraulic starter includes valves, pumps, filters, a reservoir, and piston
accumulators. The operator can manually recharge the hydraulic system; this cannot readily be done
with air or electric starting systems, so hydraulic starting systems are favored in applications wherein
emergency starting is a requirement.
Hydraulic Starter Hydraulic Starter
[edit]Other methods
Before the advent of the starter motor, engines were started by various methods
including wind-up springs, gun powder cylinders, and human-powered techniques
such as a removable crank handle which engaged the front of the crankshaft, pulling
on an airplane propeller, or pulling a cord that was wound around an open-face pulley.
The behavior of an engine during starting is not always predictable. The engine can
kick back, causing sudden reverse rotation. Many manual starters included a one-
directional slip or release provision so that once engine rotation began, the starter
would disengage from the engine. In the event of a kickback, the reverse rotation of
the engine could suddenly engage the starter, causing the crank to unexpectedly and
violently jerk, possibly injuring the operator. For cord-wound starters, a kickback could
pull the operator towards the engine or machine, or swing the starter cord and handle
at high speed around the starter pulley.
Self starting
Some modern gasoline engines with twelve or more cylinders always have at least
one piston at the beginning of its power stroke and are able to start by injecting fuel
into that cylinder and igniting it.
MagnetoFrom Wikipedia, the free encyclopedia
For other uses, see Magneto (disambiguation).
Demonstration hand-cranked magneto
A magneto is an electrical generator that uses permanent magnets to produce alternating current.
Hand-cranked magneto generators were used to provide ringing current in early telephone systems.
Magnetos adapted to produce pulses of high voltage are used in the ignition systems of some gasoline-
powered internal combustion engines to provide power to the spark plugs.[1] The magneto is now confined mainly to
engines where there is no available electrical supply, for example in lawnmowers and chainsaws. It is also universally
used in aviation piston engines even though an electrical supply is usually available. This is because a magneto
ignition system is more reliable than a battery-coil system.
Magnetos were rarely used for power generation, although they were for a few specialised uses.
Power generation
For more details on this topic, see Magneto (generator).
Magnetos have advantages of simplicity and reliability, but are inefficient owing to the
weak magnetic flux available from their permanent magnets. This restricted their use
for high-power applications. Power generation magnetos were limited to narrow fields,
such as powering arc lamps or lighthouses, where their particular features of output
stability or simple reliability were most valued.
[edit]Bicycles
One popular and common use of magnetos of today is for powering lights on bicycles.
Most commonly a small magneto, termed a bottle dynamo, rubs against the tyre of the
bicycle and generates power as the wheel turns.
More expensive and less common but more efficient is the hub dynamo.
Although commonly referred to as dynamos, both devices are in fact magnetos,
producing alternating current as opposed to the direct current produced by a
true dynamo.
[edit]Medical use
The magneto also had a medical use for treatment of mental illness in the beginnings
of electromedicine. In 1850, Duchenne, a French doctor, developed and
manufactured a magneto with a variable outer voltage and frequency, through varying
revolutions by hand or varying the inductance of the two coils, putting out or putting in
both ferromagnetic cores.
[edit]Ignition magnetos
Main article: Ignition magneto
It has been suggested that Ignition magneto be merged into this article or
section. (Discuss) Proposed since July 2011.
Magnetos adapted to produce impulses of high voltage for spark plugs are used in the
ignition systems of spark-ignition piston engines. Magnetos are used in piston aircraft
engines for their reliability and simplicity. Motor sport vehicles such
as motorcycles and snowmobiles use magnetos because they are lighter in weight
than an ignition system relying on a battery. Small internal combustion engines used
for lawn mowers, chain saws, portable pumps and similar applications use magnetos
for economy and weight reduction. Magnetos are not used in highway motor vehicles
which have a cranking battery and which may require more control over ignition timing
than is possible with a magneto system.
[edit]Telephone
1896 Telephone, hand crank for magneto on right (Sweden)
For more details on this topic, see Telephone magneto.
Many early manual telephones had a hand cranked "magneto" generator to produce a
(relatively) high voltage alternating signal to ring the bells of other telephones on the
same (party) line and to alert the operator. These were usually on long rural lines
served by small manual exchanges, which were not "common battery". The telephone
instrument was "local battery", containing two large "No. 6" zinc-carbon dry cells.
Regulator (automatic control)From Wikipedia, the free encyclopedia
In automatic control, a regulator is a device which has the function of maintaining a designated characteristic. It
performs the activity of managing or maintaining a range of values in a machine. The measurable property of a device
is managed closely by specified conditions or an advance set value; or it can be a variable according to a
predetermined arrangement scheme. It can be used generally to connote any set of various controls or devices for
regulating or controlling items or objects.
Examples are a voltage regulator (which can be a transformer whose voltage ratio of transformation can be adjusted,
or an electronic circuit that produces a defined voltage), a pressure regulator, such as a diving regulator, which
maintains its output at a fixed pressure lower than its input, and a fuel regulator (which controls the supply of fuel).
Regulators can be designed to control anything from gases or fluids, to light or electricity. Speed can be regulated by
electronic, mechanical, or electro-mechanical means. Such instances include;
Electronic regulators as used in modern railway sets where the voltage is raised or lowered to control the
speed of the engine
Mechanical systems such as valves as used in fluid control systems. Purely mechanical pre-automotive
systems included such designs as the Watt centrifugal governor whereas modern systems may have electronic
fluid speed sensing components directing solenoids to set the valve to the desired rate.
Complex electro-mechanical speed control systems used to maintain speeds in modern cars (cruise control) -
often including hydraulic components,
An aircraft engine's constant speed unit changes the propellor pitch to maintain engine speed.
[edit]See also