what is an engine a device that converts chemical energy it to mechanical energy also converts...
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What is an Engine
A device that converts chemical energy it to mechanical energy
Also converts linear force into mechanical force
Basic Engine Theory
Requires external fuel source (motor does not)
Converts chemical energy to mechanical energy
Only about 40% effecient
Generates a lot of waste heat and sound
Two-Stroke Engine Operation
Simplest design with few moving parts
Highest power/weight ratio
Ineffecient, dirty and noisy
Picture of a basic two stroke cylinder
Four-Stroke Engine Operation
This is the engine design in almost all trucks on the road
Utilizes four stroke of the piston for one complete cycle
The four strokes
The four strokes are:
Intake
Compression
Power
exhaust
Rotating vs. Reciprocating Mass
Crankshaft, flywheel, and lower portion of connecting rod are considered rotating mass
Piston and upper portion of connecting rod are considered reciprocating mass
Cams and valves also rotate and reciprocate
Combustion Chamber
the area inside the engine where the fuel/air mixture is compressed and then ignited
formed on one side by the shape cast into the cylinder head, and on the other side by the top of the piston
Combustion Chamber
THINK
When is the chamber’s dimension is at its smallest
Types of Combustion Chambers
HemisphericalThe "Hemi" Combustion Chamber• Offer the least amount of compromise for
the efficiency gained
• Hemispherical combustion chamber is one half of a sphere cast into the bottom of the cylinder head
Hemispherical design
Hemispherical
chambers
generally have
a central
spark plug
Wedge-Shaped Chambers
resembles an inclined basin recessed into the deck of the head
The relatively steep walls in such chamber design force the air/fuel flow path and deflect and force it to move in a downward spiral around the cylinder axis
Wedge-Shaped Chambers
Diesel fuel
crude oil, is naturally found in the earth
After refining, it can be separated into several different kinds of fuels, including gasoline, jet fuel, kerosene and, of course, diesel
Diesel fuel
Diesel fuel is heavier and oilier than gasoline
evaporates much more slowly
boiling point is actually higher than the boiling point of water
It evaporates more slowly because it is heavier
Diesel fuel
Diesel fuel has a higher energy density than gasoline
3.8 L of diesel fuel contains approximately 155x106 joules (147,000 BTU)
gasoline contains 132x106 joules (125,000 BTU) for 3.8L
Diesel fuel
(C8H18), typical of the molecules found in
gasoline
(C16H34), typical of diesel fuel
C is for carbon and H is for hydrogen
Diesel fuel
In a complete burn, the oxygen in the air combines with the hydrogen to form water (H2O) and with the carbon to form carbon
dioxide (CO2).
If the burning is not complete, some of the carbon atoms only combine with one oxygen atom rather than two, to form carbon monoxide (CO)
Diesel fuel
unburned hydrocarbon molecules can also come out the tailpipe
hydrocarbons react with nitrogen oxides (another pollutant from combustion) in the presence of sunlight to form ozone
Diesel fuel classification
Diesel fuel is graded and designated by the American Society for Testing and Materials (ASTM
Its specific gravity and high and low heat values are listed by the American Petroleum Institute (API).
Diesel fuel classification
Each oil refiner and supplier attempts to produce diesel fuels that comply as closely as possible with ASTM and API specifications
Due to different crude oil supplies, the diesel fuel may either be on the high or low end of the prescribed heat scale in Btu per pound or per gallon
Diesel fuel classification
There are only two recommended grades of fuel that is considered acceptable for use in high-speed heavy-duty vehicles. These are the No. 1D or No. 2D
Diesel fuel Grade:1D
Fuels within this classification are applicable for use in high- speed engines in service involving frequent and relatively wide variations in loads and speeds
In cold weather conditions, No. 1D fuel allows the engine to start easily.
Diesel fuel Grade:1D
Heavy-duty high-speed diesel vehicles operating in continued cold-weather conditions, No. 1D fuel provides better operation than the heavier No. 2D.
Require a minimum cetane number (CN)
above 40
Diesel fuel Grade:2D
Grade No. 2D has a lower volatility
This fuel is used more by truck fleets, due to its greater heat value per /L, particularly in warm to moderate climates
Has higher calorific value
Recommended for use with constant load and speed
Diesel fuel Grade:2D
Like # 1D the 2D CN is required to be above 40
Even though No. 1D fuel has better properties for cold weather operations, many still use No. 2D in the winter, using fuel heater/water separators to provide suitable starting, as well as fuel additive
Selecting the correct diesel fuel
Seven factors should be considered when selecting fuel to maximize performance and extends engine life. They are:
1. Starting characteristics
2. Fuel handling
3. Wear on injection equipment
Selecting the correct diesel fuel
4. Wear on pistons
5. Wear on rings, valves, and cylinder liners
6. Engine maintenance
7. Fuel cost and availability
Cetane Number (CN)
Cetane number is a measure of the fuel volatility; the higher the rating, the easier the engine will start and the combustion process will be smoother
The Ideal CN is 100 and a poor CN is 0
Increasing the CN decrease fuel mileage
Cetane Number (CN)
The CN rating is set by the ASTM
Current 1D and 2D diesel fuels have a cetane rating between 40 and 45.
The higher the cetane rating, the easier the fuel will ignite once injected into the diesel combustion chamber.
Cetane Number (CN)
If the cetane number is too low, you will have difficulty in starting,
Engine knock and puffs of white smoke during warm-up in cold weather.
Octane rating
Compression is one of the four strokes on a four stroke engine
The amount of compression is called the compression ratio of the engine.
Octane rating
Octane rating
The octane rating of gasoline tells much the fuel can be compressed before it
spontaneously ignites
Spontaneous ignition causes engine knock
Lower-octane gas (like "regular" 87-octane gasoline) can handle the least amount of
compression before igniting.
Octane rating
The compression ratio of your engine determines the octane rating of the gas
you must use in the car
“High-performance engine" has a higher compression ratio and requires higher-
octane fuel
87 Octane gasoline contains 87-percent octane and 13-percent heptane
Volatility
The tendency of a liquid to Vaporize
Volatility rating for diesel is crucial in summer when its higher fraction tends to boil off lowering the CN
Calorific value
This is the potential heat energy of a fuel
It is measured in BTU, Joules, or calories
Viscosity
Viscosity is the measure of a liquid’s resistance to flow
Viscosity decreases as temperature increases
This means that a fluid with a high viscosity is heavier than a fluid with low viscosity.
Viscosity
High viscosity fuel may cause extreme pressures in the injection systems and will cause reduced atomization and vaporization of the fuel spray
The viscosity of diesel fuel must be low enough to flow freely at its lowest operational temperature, yet high enough to provide lubrication to the moving parts of the finely machined injectors
Viscosity measurement
Recommended fuel oil viscosity for high-speed diesel engines is generally in the region of 39 SSU (Seconds Saybolt Universal)
This is derived from using a Saybolt Viscosimeter to measure the time it takes for a quantity of fuel to flow through a restricted hole in a tube
Cloud point
This is the temperature at which fuel begins to precipitate as wax crystal. When these crystals become large enough, the fuel will appears cloudy. This is the actual cloud point
Fire point
This is the temperature at which a fuel evaporates enough flammable vapor burn continuously in the presence of air
• Images
Flame propagation
This represents the way in which a fuel combusts inside the engine cylinder
This is determine by: the flame front, cylinder gas dynamics, AFR, temperature and fuel density
Pour point
This Generally depicts the lowest temperature at which a fuel can be pumped
Pour point is usually 3deg.C (5deg.F) to 15deg.C ( 25 deg.F) below cloud point
Specific gravity
The specific gravity of a fuel is the the weight of a volume of the fuel compared to the weight of the same volume of water.
The S.G. of petroleum base fuel is a direct measure of its heat value
Sulfur content
This is simply the amount of sulfur present in the fuelSulfur is present in most crude petroleum fuel but is more prominent in the heavier fuels such as diesel.The problem with sulfur is that when combusted, the sulfur in the fuel oxidized and form sulfur dioxide
Sulfur content
The sulfur dioxide reacts with water to form sulfuric acid
Diesel fuel as been legislated to be ultra low sulfur(ULS) fuel
Ultra low sulfur (ULS)fuel
Ultra low sulfur fuel
Ultra low sulphur diesel fuel has been refined so that its sulphur content is 15 parts per million (ppm) or less
This is 97 percent cleaner than the standard highway-use diesel fuel sold in the US, which contains an average of 500 ppm of sulphur
Ultra low sulfur fuel
The move toward ULSD is aimed at lowering diesel engines' harmful exhaust emissions and improving air quality
ULSD fuel will work with a new generation of diesel engines and exhaust system as well
Ultra low sulfur fuel
ULSD will enable the new generation of diesel vehicles to meet the same strict emission standards as gasoline-powered vehicles
The new engines will utilize an emissions-reducing device called a particulate filter
Diesel fuel subsystem
Diesel fuel subsystem
NOTE:
Diesel fuel system are usually designed to pump more fuel than is required
This value can exceed 60%
The excess fuel is used to: COOL and LUBRICATE
Fuel Tank
Fuel tanks can be made from aluminium alloy, fibreglass or steel.Most on-road mobile diesel tanks are of aluminium alloy because of its lighter weight and less susceptible to corrosion Tanks must be strategically installed for vehicle balancingFuel tanks are OEM responsibility
Fuel Tank
Fuel tanks also contains Baffles to prevent the fuel from sloshing around when the vehicle is moving
Fuel Tank Recommendations
Need to be located in the air flowMost tanks are cradle mounted to the side of the frame rails to ensure thisGood air flow means good heat exchange from the fuel to the atmosphere When fuel temperatures climb above 95°F, there can be a noticeable loss of power because fuel density drops.
Fuel Tank Recommendations
The best shape is CYLINDRICAL because it
Maximize The surface area of the exposed area of the tank( Quest. Why is this important)
Stronger base on the law of physics (question: Tell me why)
Fuel Tank Recommendations
Fuel should be kept at minimum of 25 % full (Quest. Why)A galvanized steel fuel tank should never be used for fuel storage because diesel fuel reacts chemically with the zinc coating to form powdery flakes that clogs fuel filters and damage fuel pumps and injectors
Dual Fuel Tanks
Usually two tanks mounted on opposite sides of the frame railBoth tanks of equal size and shape to maintain even weight distributionFuel is fed to the engine from both tanksFuel is return to both tanksNote a single pick up tube can be used with a cross over pipe.(old technology)
Pick up tube
Usually positioned slightly above the base of the tank to avoid picking up water or dirt
When or if failed, it can cause the fuel to be aerated
Fuel Tank Ventilation
As fuel is sucked out of the tanks air is drawn in
As fuel is returned to the tanks the air is forced out
This air movement prevent the tank from in a vacuum or from been under pressure.
Fuel Tank Ventilation
At this time diesel tanks are equipped with vents that allow free movement of air into and out of the tank to atmosphere.
Water in fuel
Water in Fuel (WIF) should be periodically checked base on the OEM recommendation
Water in the tank can be checked By: inserting an aluminum rod slightly coated with water detection paste in the fuel tank
Remove rod and inspect for a change in color
Fuel sending unit
This sending unit is mounted in side the tank
It consist of a floating and a arm connected to a variable resistor
The resistor controls the current to the cab gauge proportionally with the fuel level.
Filter Clean Fuel
Fuel filters are rated by their ability to trap particles
They function like a strainer allowing only particle of a certain size to pass through
The unit we use to measure particle is micron.
1 micron = 1 millionth of a meter
Filter Clean Fuel
A typical secondary filter filters down to 5 micron
So any solid 5 micron or bigger will be trapped
NOTE
A human eye is unable to see particles smaller than 40 micron in size
Filter Clean Fuel
Example: a fuel filter with a rating of 2micron at 99% means it will trapped particle 2micron or larger 99%of the time
Fuel Lines
Fuel lines bring the fuel from the tank to the engine and return surplus fuel from the engine to the tank. Tubing, hoses, and fittings have to meet temperature, pressure, chemical, and physical requirements for each part of an installation.
Fuel Lines
Fuel lines may be under relatively low pressure or no pressure such as is the case in return lines bringing fuel back to the tank Supply lines from the tank to the transfer pump are under suction
Fuel Lines
Fuel Lines
Lines from the transfer pump to the injection equipment are under moderate pressure usually ranging from approximately 3 to 75psi depending on the system although some new systems operate at higher pressures, up to 265 psi.
Fuel Lines
Copper tubing is not recommended for any fuel system. This tubing hardens and breaks in a relatively short time in diesel installations Some steel tubing is copper-coated to prevent excessive corrosion and to add resiliency. Copper-coated tubing must not be mistaken for copper tubing.
High pressure fuel line
Pump line nozzle system such as the inline pump system use high pressure fuel lines These are usually made of heavy-wall steel tubing and must be capable of handling fuel pressures as high as 24,000 psi
High pressure fuel line
Pump line nozzle is between the injection pump and the injectors.
Fuel line inspection
Inspect the fuel lines periodically for loose connections, breaks, or other flaws Fuel lines must be replaced if they are worn, damaged, or deteriorated
Fuel Subsystem Operating Fundamentals
There are several different types of high pressure injection equipment
Inline pump
The inline pump consisting of an individual pump element for each cylinder all contained in a single housing,
Distributor pump
Distributor style pumps which use a single pump element for all cylinders which was common on smaller engines
Unit injection systems
MUI, (mechanical unit injector), EUI, (electronically controlled unit injector), HEUI, (hydraulically actuated electronically controlled unit injector)
Unit injection systems
Unit injection systems
The EUI and HEUI are the most common system todayEUI and HEUI systems have individual unit injectors for each cylinder They are called unit injectors because they are responsible for pressurizing metering and atomizing the fuel
Electronic Unit Pump(EUP)
EUP, (Electronic Unit Pump), these systems have individual pumps for each cylinder
The pumps are driven off the engine camshaft
Common rail fuel system
Common rail injection systems use an accumulator rail that retains fuel at injection pressures and delivers it to the injectors There are other proprietary systems in use such as Cummins PT, (Pressure Time), system, Cummins HPI-TP, (High Pressure Injection - Time Pressure), Cummins Accumulator Pump Systems.
Low Pressure Supply System
designed to provide an unrestricted supply of fuel to the transfer pump and the fuel injection pump
Transfer Pump
Transfer pumps must be capable of providing maximum fuel flow at idle speeds
At high speeds the pumps provide much more flow than is required so the pump must have a regulating system of one kind or another in order to limit its maximum pressure
Transfer Pump
Fuel transfer pump can be Driven by
The cam shaft
Gear driven by an accessory
Electric pump controlled by the ECM
Mechanically Operated Diaphragm Transfer Pump
Consists of an actuator arm; a lever-operated, spring-loaded diaphragm; an inlet valve; and an outlet valve The engine's camshaft has an eccentric that applies power to the pump's actuator arm.
Mechanically Operated Diaphragm Transfer Pump
As the diaphragm is pulled down, a low pressure area is created above it This causes the higher atmospheric pressure in the tank to push fuel past the inlet valve into the centre chamber of the pump
Mechanically Operated Diaphragm Transfer Pump
As the diaphragm is forced back up by the spring, the pressure above the diaphragm increases This pressure closes the inlet valve and opens the outlet valve, forcing fuel to travel through the pump outlet and into the injector pump.This pump pressure max. at about 7PSI
Mechanically Operated Diaphragm Transfer Pump
Plunger Transfer Pump
This transfer pump is a higher pressure pump Usually mounted on the injection pump housing The injection pump camshaft actuates the pump's plunger There are two types of plunger pumps single and dual acting.
Plunger Transfer Pump
Gear Transfer Pump
The gear transfer pump is a positive-displacement pump generally driven directly from the end of the governor shaft. A built-in regulating valve prevents damage to the injection equipment in the event of an obstruction in the fuel supply system
Gear Transfer Pump
The fuel pump body is recessed to provide running space for the pump gearsRecesses are also provided at the inlet and outlet cavities An overflow valve returns excess fuel to the supply tank
Gear Transfer Pump
When the discharge pressure is great enough to move the relief valve back from its seat, fuel re-enters the suction side of the pump controlling the maximum pressure
Gear Transfer Pump
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