thermal engg-i lab manual

8/13/2019 Thermal Engg-I Lab Manual

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E X P E R I M E N T N O . 1

AIM : Comparative study of four stroke diesel and petrol engines.

BASIC CONCEPT :

An internal combustion engine cycle completed in four piston strokes; includes a suction stroke,

compression stroke, expansion stroke, and exhaust stroke.

The four-stroke cycleof aninternal combustion engine is the cycle most commonly used for automotive

and industrial purposes today (cars and trucks, electrical generators, etc). The Thermodynamics cycles

used in internal combustion reciprocating engines are the Otto Cycle (the ideal cycle for spark-ignition

engines) and the Diesel Cycle (the ideal cycle forcompression-ignition engines).

The Otto Cycle consists ofadiabatic compression, heat addition at constant volume, adiabatic expansionand rejection of heat at constant volume.

The four-stroke cycle is more fuel efficient and clean burning than the two-stroke cycle, but requires

considerably more moving parts and manufacturing expertise. Moreover, it is more easily manufactured

in multi-cylinder configurations than the two-stroke, making it especially useful in high-output

applications such as cars.

Four Stroke Petrol Engine:

The Otto cycle is characterized by four strokes or straight movements alternately, back and forth, of apiston inside acylinder:

Intake (Suction) Stroke

Compression Stroke

Power (Combustion) Stroke

Exhaust Stroke

The cycle begins attop dead centre(TDC), when the piston is furthest away from thecrankshaft.On thefirst stroke (intake) of the piston, a mixture offuel andair is drawn into the cylinder through the intake

(inlet) port. The intake (inlet) valve (or valves) then close(s) and the following stroke (compression)

compresses the fuel-air mixture.
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PROCEDURE

Working of Four Stroke Petrol Engine:

The four-stroke engine is so-called because in each cycle, the piston makes four strokes or up/downmotions in the cylinder (i.e., it goes down, up, down, up). The four strokes are:

1. Intake stroke: The piston moves down increasing the volume inside the cylinder. During this stroke,

the inlet valve is open allowing fuel-air mixture to be sucked into the cylinder. Because the system isopen, this is a constant pressure process atP ~ 1 atm.

2. Compression stroke: The piston moves back up with both inlet and outlet valves closed, compressingthe fuel airmixture. This is a very rapid process, one that is adiabatic (constant Q), resulting in a

significant temperature increase in the fuel-air mixture (in a diesel engine, this heating is sufficient to

auto-ignite the fuel).

3. Power stroke: The piston moves back down with both inlet and outlet valves closed, this is also an

adiabatic process. Normally the engine fires at the end of the compression stroke and the heat generatedby the burning fuel provides work by expanding and pushing the piston down.

4. Exhaust stroke: The piston moves back up with the outlet valve open, pushing the exhaust gases or

unburnt fuel-air mixture out of the chamber at constantP ~ 1 atm.


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Efficiency of an ideal Otto cycle

In the ideal Otto cycle, the intake-exhaust branch contains no area, and so as far as the

work and efficiency is concerned. This gives us a four-branch cycle A-B-C-D-A as shown

in Fig., which consists of an adiabatic compression during the compression stroke (AB), a

constant volume increase in pressure when the combustion occurs (B-C), an adiabatic expansion during

the power stroke (C-D) and a constant volume decrease in pressure as the exhaust cools before the

exhaust stroke (D-A).

As shown in Fig. , the heat Qhcomes in during combustion (B-C), and produces work W (given by the

PV-area enclosed in the cycle) and some waste heat Qc, which leaves the system during the cooling stage

(D-A). In ideal cycle no heat enters or leaves the system

during the compression (A-B) and power (C-D) strokes because these processes are adiabatic.

Efficiency of Otto cycle= 1- (TD / TC) = 1- (TA / TB) = 1- (V2/V1)-1

Study Of Four Stroke Diesel Engine

Four-Stroke Diesel Engine- The four-stroke diesel engine is similar to the four stroke gasoline engine.

They both follow an operating cycle that consist of intake, compression, power, and exhaust strokes. Theyalso share similar systems for intake and exhaust valves.

The primary differences between a diesel engine and a gasoline engine are as follows:

The fuel and air mixture is ignited by the heat generated by the compression stroke in a diesel engineversus the use of a spark ignition system on a gasoline engine.

The fuel and air mixture in a diesel engine is compressed to about one twentieth of its originalvolume,

while in a gasoline engine the fuel and air mixture is only compressed to about one eighth of its original


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volume. The diesel engine must compress the mixture more tightly to generate enough heat

to ignite the fuel and air mixture. The contrast between the two engines is shown in figure

1-7.

The gasoline engine mixes the fuel and air before it reaches the combustion chamber. A diesel engine

takes in only air through the intake port. Fuel is put into the combustion chamber directly through aninjection system. The air and fuel then mix in the combustion chamber.

The engine speed and the power output of a diesel engine are controlled by the quantity of fuel admittedto the combustion chamber. The amount of air is constant. On the gasoline engine, the speed and power

output is regulated by limiting the air and fuel mixture entering the engine.

A diesel engine is much more efficient than a gasoline engine, such as the diesel engine does not require

an ignition system due to the heat generated by the higher compression, the diesel engine has a better fuel

economy due to the complete burning of the fuel, and the diesel engine develops greater torque due to the

power developed from the high-compression ratio.

Viva Related Questions:

1. What is difference between Otto Cycle and Diesel Cycle?2. What do you mean by Four Stroke?3. What is difference between Four stroke and Two Stroke Engine?4. Where is Four stroke Petrol Engine used?5. Explain Intake, Compression, Power and Exhaust Stroke of Four stroke Petrol Engine?6. What is efficiency of Otto Cycle?7. On which factors efficiency of Otto Cycle depends and how we can improve it?8. Explane the compression ration in engine?


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AIM:Comparative study of two stroke petrol and diesel engines

BASIC CONCEPT:

The two-stroke engine is simpler mechanically than the four-stroke engine. The two-stroke engine

delivers one power stroke every two strokes instead of one every four; thus it develops more power with

the same displacement, or can be lighter and yet deliver the same power. For this reason it is used in lawn

mowers, chain saws, small automobiles, motorcycles, and outboard marine engines.

The two stroke engine employs the crankcase as well as the cylinder to achieve all the elements of the

Otto cycle in only two strokes of the piston.

Intake. The fuel/air mixture is first drawn into the crankcase by the vacuum created during the upwardstroke of the piston. The illustrated engine features a poppet intake valve, however many engines use a

rotary value incorporated into the crankshaft.

During the downward stroke the poppet valve is forced closed by the increased crankcase pressure. The

fuel mixture is then compressed in the crankcase during the remainder of the stroke.

Transfer/Exhaust. Toward the end of the stroke, the piston exposes the intake port, allowing the

compressed fuel/air mixture in the crankcase to escape around the piston into the main cylinder. This


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expels the exhaust gasses out the exhaust port, usually located on the opposite side of the

cylinder. Unfortunately, some of the fresh fuel mixture is usually expelled as well

Compression.The piston then rises, driven by flywheel momentum, and compresses the

fuel mixture. (At the same time, another intake stroke is happening beneath the piston).

Power.At the top of the stroke the spark plug ignites the fuel mixture. The burning fuel expands, drivingthe piston downward, to complete the cycle

Since the two stroke engine fires on every revolution of the crankshaft, a two stroke engine is usually

more powerful than a four stroke engine of equivalent size. This, coupled with their lighter, simpler

construction, makes two stroke engines popular in chainsaws, line trimmers, outboard motors,

snowmobiles, jet-skis, light motorcycles, and model airplanes. Unfortunately most two stroke engines

are inefficient and are terrible polluters due to the amount of unspent fuel that escapes through the exhaust

port


1. What is difference between Otto Cycle and Diesel Cycle?2. What do you mean by Four Stroke?3. What is difference between Four stroke and Two Stroke Engine?4. Where is Four stroke Petrol Engine used?5. Explain Intake, Compression, Power and Exhaust Stroke of Four stroke Petrol Engine?6. What is efficiency of Otto Cycle?7. On which factors efficiency of Otto Cycle depends and how we can improve it?8. Explane the compression ration in engine?

Study of Two Stroke Diesel Engine.

Theory:

There is a big difference between two-stroke andfour-stroke engines is the amount of power the engine

can produce. The spark plug fires twice as often in a two-stroke engine -- once per every revolution of the

crankshaft, versus once for every two revolutions in a four-stroke engine. This means that a two-stroke

engine has the potential to produce twice as much power as a four-stroke engine of the same size.

It turns out that the diesel approach, which compresses only air and then injects the fuel directly into the

compressed air, is a much better match with the two-stroke cycle. Many manufacturers of large diesel

engines therefore use this approach to create high-power engines.

The figure below shows the layout of a typical two-stroke diesel engine:
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At the top of the cylinder are typically two or four exhaust valves that all open at the same time. There is

also the diesel fuel injector (shown above in yellow). The piston is elongated, as in a gasoline two-stroke

engine, so that it can act as the intake valve. At the bottom of the piston's travel, the piston uncovers the

ports for air intake. The intake air is pressurized by a turbocharger or asupercharger (light blue). The

crankcase is sealed and contains oil as in a four-stroke engine.

The two-stroke diesel cycle goes like this:

When the piston is at the top of its travel, the cylinder contains a charge of highly compressed air. Diesel

fuel is sprayed into the cylinder by the injector and immediately ignites because of the heat and pressureinside the cylinder. This is the same process described inHow Diesel Engines Work.

The pressure created by the combustion of the fuel drives the piston downward. This is the power stroke.

As the piston nears the bottom of its stroke, all of the exhaust valves open. Exhaust gases rush out of the

cylinder, relieving the pressure.

As the piston bottoms out, it uncovers the air intake ports. Pressurized air fills the cylinder, forcing out the

remainder of the exhaust gases.

The exhaust valves close and the piston starts traveling back upward, re-covering the intake ports and

compressing the fresh charge of air. This is the compression stroke.

As the piston nears the top of the cylinder, the cycle repeats with step 1.
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From this description, you can see the big difference between a diesel two-stroke engine and a gasolinetwo-stroke engine: In the diesel version, only air fills the cylinder, rather than gas and air mixed together.

This means that a diesel two-stroke engine suffers from none of the environmental problems that plague a

gasoline two-stroke engine. On the other hand, a diesel two-stroke engine must have aturbocharger or a

supercharger, and this means that you will never find a diesel two-stroke on a chain saw -- it would

simply be too expensive. Unlike a gasoline engine, which requires a spark plug to ignite the fuel/air

charge in the cylinder, a diesel engine relies solely on the heat of compression for ignition. Fuel is

injected at high pressure into the superheated compressed air and instantly ignites. Therefore, scavenging

is performed with air alone.
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Figure 1-13.Two-stroke cycle diesel engine.Two-Stroke Cycle Diesel Engine

A two-troke diesel engine (fig. 1-13) shares the same operating principles as other internal

combustion engines. It has all of the advantages that other diesel engines have over gasoline engines

A two-stroke diesel engine does not produce as much power as a four-stroke diesel engine; however, it

runs smoother than the four-stroke diesel. This is because it generates a power stroke each time the

piston moves downward; that is, once for each crankshaft revolution. The two-stroke diesel engine has a

less complicated valve train because it does not use intake valves. Instead, it requires a supercharger toforce air into the cylinder and force exhaust gases out, because the piston cannot do this naturally as in

four-stroke engines.

The two-stroke diesel takes in air and discharges exhaust through a system called scavenging.

Scavenging begins with the piston at bottom dead center. At this point, the intake ports are uncovered

in the cylinder wall and the exhaust valve is open. The supercharger forces air into the cylinder, and, as

the air is forced in, the burned gases from the previous operating cycle are forced out (fig. 1-14)

COMPRESSION STROKE. As the piston moves towards top dead center, it covers theintake ports. The exhaust valves close at this point and seals the upper cylinder. As the piston continues


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upward, the air in the cylinder is tightly compressed (fig. 1-14). As in the four-stroke

cycle diesel, a tremendous amount of heat is generated by the compression.

POWER STROKE. As the piston reaches topdead center, the compressionstroke ends. Fuel is injected at this point and the intense heat of the compression

causes the fuel to ignite. The burning fuel pushes the piston down, giving power to the crankshaft. The

power stroke ends when the piston gets down to the point where the intake ports are uncovered. At aboutthis point, the exhaust valve opens and scavenging begins again, as shown in figure 1-14


1. What is difference between Otto Cycle and Diesel Cycle?2. What do you mean by Four Stroke?3.

What is difference between Four stroke and Two Stroke Engine?

4. Where is Four stroke Petrol Engine used?5. Explain Intake, Compression, Power and Exhaust Stroke of Four stroke Petrol Engine?6. What is efficiency of Otto Cycle?


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Object:Studies of fuel supply systems of diesel and petrol engines.

Theory:

DIESEL FUEL SYSTEM:

Diesel Fuel System The primary job of the diesel fuel system is to inject a precise amount of atomized

and pressurized fuel into each engine cylinder at the precise time. The major parts of the diesel system are

the fuel tank, fuel transfer pump, fuel filters, injection pump, and injection nozzles.

Fuel Transfer PumpThe fuel transfer pump is normally used on modern high-speed diesel engines. It

can be driven by either engine or battery voltage. The fuel transfer pump can be located on the outside ofthe fuel tank in the supply line, submerged within the fuel tank, or mounted on the backside of the

injection pump. The fuel pump pushes or draws the fuel through the filters where the fuel is cleaned.

Injection PumpSeveral types of injection pumps are used on diesel engines. Each has its own unique

operating principles. The primary function of the injection pump is to supply high-pressure fuel forinjection.

Injection NozzlesA wide variety of injector nozzles are in use today. All are designed to perform the

same basic function which is to spray the fuel in atomized form into the combustion chamber of each

cylinder.

Cold Weather Starting Aids Diesel fuel evaporates much slower than gasoline and requires more

heat to cause combustion in the cylinders of the engine. For this reason, preheater and starting aids,

called glow plugs, are installed on equipment equipped with diesel engines.


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The camshaft is made to rotate with the crankshaft through the timing gears. The cam lobe

is the raised portion on the camshaft that contacts the bottom of the lifter. As the cam

rotates, the lobe pushes up on the lifter. The cam lobe pushes the valve open against the

pressure of a spring. As the cam lobe rotates away from the lifter, the valve spring pulls the

valve closed. The proper positioning of the cam lobes on the camshaft establishes a

sequence for the intake and exhaust valves.

FUEL SYSTEMS:

The function of the fuel system is to ensure a quantity of clean fuel is delivered to the fuel intake of

an engine. The system must provide both safe fuel storage and transfer

FUEL TANKS:


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Fuel tanks store fuel in liquid form. The tank may be located in any part of a vehicle that is

protected from flying debris, shielded from collisions, and not likely to bottom out (fig. 1-

16). Most wheeled vehicles use removable fuel tanks.

Most fuel tanks are made of thin sheet metal coated with a lead-tin alloy to prevent

corrosion. Fiber glass and a variety of molded plastics are also popular as corrosion-resistant materials.

Fuel Supply System:

For most of the existence of the internal combustion engine, the carburetor has been the device that

supplied fuel to the engine. On many other machines, such as lawnmowers andchainsaws,it still is. But

as the automobile evolved, the carburetor got more and more complicated trying to handle all of the

operating requirements. For instance, to handle some of these tasks, carburetors had five different circuits:

Main circuit - Provides just enough fuel for fuel-efficient cruising

Idle circuit - Provides just enough fuel to keep the engine idling

Accelerator pump - Provides an extra burst of fuel when the accelerator pedal is first depressed, reducing

hesitation before the engine speeds up

Power enrichment circuit - Provides extra fuel when the car is going up a hill or towing a trailer

Choke - Provides extra fuel when the engine is cold so that it will start

In order to meet stricter emissions requirements, catalytic converters were introduced. Very careful

control of the air-to-fuel ratio was required for the catalytic converter to be effective. Oxygen sensors

monitor the amount of oxygen in the exhaust, and the engine control unit (ECU) uses this information to

adjust the air-to-fuel ratio in real-time. This is called closed loop control -- it was not feasible to achieve

this control with carburetors. There was a brief period of electrically controlled carburetors before fuelinjection systems took over, but these electrical carbs were even more complicated than the purely

mechanical ones.

At first, carburetors were replaced with throttle body fuel injection systems (also known as single point or

central fuel injection systems) that incorporated electrically controlled fuel-injector valves into the throttle

body. These were almost a bolt-in replacement for the carburetor, so the automakers didn't have to make

any drastic changes to their engine designs.

Gradually, as new engines were designed, throttle body fuel injection was replaced by multi-port fuel

injection (also known as port, multi-point or sequential fuel injection). These systems have a fuel injector

for each cylinder, usually located so that they spray right at the intake valve. These systems provide moreaccurate fuel metering and quicker response


1. Explain the Fuel supply system in Petrol engine?2. Explain the Fuel supply system in Diesel engine?
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Object:Study of cooling, lubrication and ignition system in diesel andpetrol engines.

Theory:

Engine Lubrication System:

The engine lubrication system consists of oil pump, oil filter, oil filler cap, oil dipstick, and oil pan. The

oil pan at the engine bottom holds the oil. The oil pump forces the oil through the filter and internal

passages of engine, and then the oil drains back the oil pan through other passages.

Oil is used to lubricate the moving parts of a engine. Oil clean dirt and impurities from the engine into

the filter and prevent them from moving back to the engine. Oil can also remove part of the heat from the

engine. Therefore, changing engine oil frequently will pre long the engine lifetime.

Two-stroke engines often have a simple lubrication system in which a special two-stroke oil is mixed

with the fuel, (then known as 'petroil' from "petrol" + "oil") and therefore reaches all moving parts of theengine. Handheld devices using this method of lubrication have the advantage of operating in any

orientation since there is no oil reservoir which would be dependent upon gravity for proper function.

Depending on the design of the engine system, the oil can be mixed with the fuel manually each time fuel

is added, or an oil pump can automatically mix fuel and oil from separate tanks.

The engine uses cylinder port valves which are incompatible with piston ring seals. This causes lubricant

from the crank to work its way into the combustion chamber where it burns. Research has been conducted

on designs that attempt to reduce the combustion of lubricant. This research could potentially produce an

engine having very valuable properties of both high specific-power and low pollution.
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Lubrication System:

Engine Lubrication:

Lubrication is provided for engines in order to:

reduce friction reduce wear cool the moving parts

Lubricating oil is classified according to its viscosity. Viscosity is the resistance to flow in oil. A thick

oil (SAE 40) has a high viscosity and flows easily only at high temperatures; used in engines that run hot.

A thin oil (SAE 10) has a low viscosity and flows easily when cold; it is used in cold weather and for

cool running engines. The letter "W" indicates an oil is rated for winter temperature and will flow easily

at low temperature. A multi-grade (mixture) oil is indicated by 60/40; this does not in an oil of SAE 50

(duh!). Viscosity is affected by temperature; a high oil temperature lowers an oil's viscosity (therefore, it

flows more freely).This section covers the various types of lubrication systems found in outboard andinboard (4-stroke petrol or diesel and 2-stroke diesel) engines. The section concludes with maintenance

and fault finding procedures for theses systems.

Lubrication for the 2-stroke Petrol Engine

1.Splash System 2.Pressurized System .3 Dry Sump Lubrication System

Lubrication - Splash System:

In this simple system (not illustrated) the crankshaft dips into the sump as it rotates. Lubricating oil is

splashed onto the cylinder walls, the piston, and the small-end bearing. Some oil will pass down a hole in

the crankweb to the main bearings. This method is only used for slow running, low powered engines.

Lubrication - Pressurized System:
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General Operation - In the pressurized lubrication system oil is pumped under pressure through the

bearings and then splashes out onto the cylinder walls and drains into the sump. Friction and wear is

reduced by the film of oil. Cooling also occurs as the oil also removes heat from the bearings and metal

surfaces. Sometimes a sea water cooled oil cooled may be fitted on large engines to maintain oil viscosityas a satisfactory level.

Oil Storage & Filtration- The oil is stored in the sump and is drawn out by a gear driven oil pump after

having passed through an oil strainer. The oil then passes through a filter to remove even the smallest

pieces of dirt and grit. This filter is either a by-pass filter (where only some of the oil is filtered) or a full-

flow filter (where all of the oil is filtered). Note: a magnet is sometimes fitted inside an oil filter to

remove iron particles from the oil.

Oil Circulation- The clean, filtered oil then passes to the main galley (a large pipe) which feeds smaller

galleries (pipes) that lead to the main bearings, camshaft, etc. Pressure in the system is approximately 3

bar (45 pounds per square inch). A pressure relief value is fitted in the pipeline to release excess oil to the


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sump if the pressure is too high. After passing to the main bearings the oil travels down

small passages inside the crankshaft to the big end bearings. From the big end bearings it

drains to the sump.

Oil Level & Pressure- The sump stores the oil and allows it to cool. The correct quantity of oil must

therefore be present in the sump. This must be checked by reading the sump level with the dipstick. Thesump level must always be checked before the engine is run. Oil pressure may be indicated by a gauge or

a warning light (which comes on to warn of low oil pressure).

Lubrication - Gear Driven Oil Pump:

A gear driven oil pump is often used in a pressurized lubrication system. This pump, is normally located

between the sump and the oil filter (see previous illustration). In this pump the interconnecting gear

wheels mesh and rotate in a closely fitted casing. The oil enters and is trapped between the gear teeth and

the casing as the gear wheels rotate. Oil discharge takes place on the opposite side from the suction.

Lubrication - Dry Sump System:

In this arrangement, used on larger inboard engines, a separate tank, outside the engine is used to store

lubricating oil. A scavenge pump is used to draw out oil drainage from the engine and pass it to the

outside storage tank. Another oil pump, of smaller capacity, them pumps the oil to the engine for

lubrication. The sump is not actually dry but it will never have any quantity of oil in it. The oil supply for

this type of system is considered to

be more positive for an engine

that inclines.

Ignition system:

The ignition system of aninternal-combustion engine is an important part of the overall engine system

that provides for the timely burning of the fuel mixture within the engine. All conventional petrol
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(gasoline) engines require an ignition system. The ignition system is usually switched

on/off through alockswitch,operated with akey or code patch.

Types of Ignition System:

1. Magneto system:

The simplest form of spark ignition is that using amagneto.The engine spins amagnet inside a coil, and

also operates a contact breaker, interrupting the current and causing the voltage to be increased

sufficiently to jump a small gap. The spark plugs are connected directly from the magneto output.

Magnetos are not used in modern cars, but because they generate their own electricity they are often

found on piston aircraft engines and small engines such as mopeds, lawnmowers, snowblowers,

chainsaws, etc. where there is no battery; also on the small engine's ancestor, thestationary "hit or miss"

engine (variously called "hit and miss") of the early twentieth century; on older gasoline or distillate farm

tractorsbefore battery starting and lighting became common; and also inaircraft piston engines, where

their simplicity and self-contained nature confers a generally greater reliability as well as lighter weight in

the absence of a battery and generator or alternator.

2. Battery operated ignition:

With the universal adaptation of electrical starting for automobiles, and the concomitant availability of a

large battery to provide a constant source of electricity, magneto systems were abandoned for systems

which interrupted current at battery voltage, used anignition coil (a type ofautotransformer)to step the

voltage up to the needs of the ignition, and adistributor to route the ensuing pulse to the correct spark

plug at the correct time. This ignition was developed by Charles Kettering and was a wonder in its day. It

consisted of a single coil, points (the switch), a capacitor and a distributor set up to allocate the spark

from the ignition coil timed to the correct cylinder. The coil was basically an autotransformer set up to

step up the low (6 or 12V) voltage supply to the high ignition voltage required to jump a spark plug gap.The points allow the coil to charge magnetically and then, when they are opened by a cam arrangement,

the magnetic field collapses and a large (20KV or greater) voltage is produced. The capacitor is used to

absorb the back EMF from the magnetic field in the coil to minimize point contact burning and maximize

point life. The Kettering system became the primary ignition system for many years in the automotive

industry due to its lower cost, higher reliability and relative simplicity.

The purpose of the ignition system is to light the fuel/air mixture on fire at the right time.

Three types of systems have been used in modern times:

The Breaker Point System The Electronic System The Computerized System The Distributorless System
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All ignition systems have two circuits;

The Primary Circuit:

The primary circuit is the low voltage circuit that controls the ignition systemTHE PRIMARY CIRCUIT CONSISTS OF

Battery - provides the power to run the system.

Ignition switch - allows the driver to turn the system on and off.

Ballast resistor - reduces battery voltage from 12 volts to 9 volts.

Points - a mechanical switch that acts as the triggering mechanism.

Condenser - protects the points from burning out.

Primary coil - produces the magnetic field which creates the high voltage in the secondary

coil.

Wires - join all the components together.

The Secondary CircuitThe secondary circuit is the circuit which converts magnetic induction into high

voltage electricity to jump across the spark plug gap, firing the mixture at the right time.

The Secondary Circuit consists of:

Secondary coil - the part of the coil that creates the high voltage electricity.

Coil wire - a highly insulated wire, that takes the high voltage from the coil, to the

distributor cap.

Distributor cap - a plastic cap which goes on top of the distributor, to hold the high tension


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wires in the right order.

Rotor - spins around on the top of the distributor shaft, and distributes the spark to the rightspark plug.

Spark plug wires - another highly insulated wire that takes the high voltage from the cap to

the plugs.

Spark plugs - take the electricity from the wires, and give it an air gap in the combustion

chamber to jump across, to light the mixture.

Principles:

1. When electricity flows through a wire, a magnetic field is built up around the wire.

2. When a wire passes through magnetic lines of force, cutting them, a voltage is induced inthe wire.

3. Three things are needed to produce electricity:

1. Magnetic field

2. Circuit - a path for the electricity to go through.

3. Motion - either the wire, or the magnetic field, has to move.

Electrons, supplied by the battery when the engine is starting or by the alternator when

the engine is running, are supplied to the primary circuit at about 12 volts electrical pressure.When the circuit is completed by turning on the ignition switch, and the breaker points are

closed, those electrons flow through the primary coil, across the points to ground, and back to

the battery again.


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When electrons flow through a wire, a magnetic field is built up around the

wire. Make the wire into a coil, and the magnetic field increases by the number of

loops in the coil. This magnetic field takes a relatively long period of time to

build up. it isn't instantaneous. The time the coil is charging up is called coil

saturation, and is controlled by the amount of time the breaker points are closed,

or "dwell". The longer the points are closed for, the longer the dwell, and the stronger the

magnetic field becomes.

The coil is actually named wrong. It shouldn't be called the coil. it should be called the

"coils". The primary coil is the one that builds up the magnetic field. it has a few hundred turns

of relatively large wire in it.. The secondary coil has a few thousand turns of small diameter

wire in it because it is the one that will make the high voltage, but low current, and fire thespark plugs.

So when the points are closed and the ignition switch is turned on, a magnetic field is

built up around the coil. When the points are opened by the distributor cam, electrons can no

longer flow, so the magnetic field collapses toward the center of the coil at the speed of light.

When it collapses, it moves through the secondary coil. Since the secondary coil has so many

turns of wire, and the speed of the magnetic field is so high, a great deal of voltage is induced

into it.

Not al l of the electrical energy is actually used though. Voltage only builds up unti l there

is enough to ionize the air in the gap between the positive and ground electrodes of the spark

plug. when there is enough voltage the spark plug fires and releases the energy to ground. itwill always take between 5,000 (5kv) and 15,000 (15kv) volts to jump across the spark plug

gap. if it takes more, there is too much resistance in the plug circuit, or there is too wide a

spark plug gap. if it takes less than 5kv to fire the plug, there is a short, caused by a shorted

plug wire, too small a spark plug gap, or a fouled plug.

the high voltage electricity produced in the secondary coil goes from the coil tower,

through the coil high tension wire to the distributor cap, from the center of the cap across the

rotor to the outer terminal of the cap, through the spark plug high tension wire to the spark

plug, across the plug gap to ground firing the mixture in the combustion chamber. this al l ta kes

place at the speed of light.


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the coil is actually a transformer. it transforms a twelve volts or so, into as

much as 45,000 volts.

a breaker point ignition system is capable of producing between 20,000 and 30,000 volts of

electrical pressure. there is very little actual current flow.

electronic ignition systems were first used as standard equipment in 1975 because of the

50,000 mile emission durability test required by the environmental protection agency. the

problem with the old system which had been used for seventy five years, was the points,

which started to deteriorate after 1,000 miles, and were totally worn out by 20,000 miles. an

electronic ignition system uses a transistor to turn on and off primary power. transistors are

electronic switches that either work or don't, they don't just deteriorate in use. electronic

systems are capable of producing up to 45,000 volts and much higher amounts of current

than the breaker point system.

the spark will take place just before top dead ce nter on the compression stroke

Cooling System:

Engine Cooling, Air-intake and Starting Systems

The cooling system in most cars consists of the radiator and water pump. Water circulates through

passages around the cylinders and then travels through the radiator to cool it off. In a few cars (most

notablyVolkswagen Beetles), as well as mostmotorcycles and lawn mowers, the engine is air-cooled

instead (You can tell an air-cooled engine by the fins adorning the outside of each cylinder to helpdissipate heat.). Air-cooling makes the engine lighter but hotter, generally decreasing engine life and

overall performance. SeeHow Car Cooling Systems Work for details.

Diagram of a cooling system
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Most cars are normally aspirated, which means that air flows through an air filter and

directly into the cylinders. High-performance engines are either turbocharged or

supercharged, which means that air coming into the engine is first pressurized (so that

more air/fuel mixture can be squeezed into each cylinder) to increase performance. The

amount of pressurization is called boost.Aturbocharger uses a small turbine attached to

the exhaust pipe to spin a compressing turbine in the incoming air stream. A supercharger is attached

directly to the engine to spin the compressor.

The Basics

Inside your car's engine, fuel is constantly burning. A lot of the heat from this combustion goes right out

the exhaust system, but some of it soaks into the engine, heating it up. The engine runs best when its

coolant is about 200 degrees Fahrenheit (93 degrees Celsius). At this temperature:

The combustion chamber is hot enough to completely vaporize the fuel, providing better combustion and

reducing emissions.

The oil used to lubricate the engine has a lower viscosity (it is thinner), so the engine parts move more

freely and the engine wastes less power moving its own components around.

Metal parts wear less.

There are two types of cooling systems found on cars: liquid-cooled and air-cooled.

Liquid Cooling

The cooling system on liquid-cooled cars circulates a fluid through pipes and passageways in the engine.

As this liquid passes through the hot engine it absorbs heat, cooling the engine. After the fluid leaves the

engine, it passes through a heat exchanger, or radiator, which transfers the heat from the fluid to the air

blowing through the exchanger.

Air Cooling

Some older cars, and very few modern cars, are air-cooled. Instead of circulating fluid through the engine,

the engine block is covered in aluminum fins that conduct the heat away from the cylinder. A powerful

fan forces air over these fins, which cools the engine by transferring the heat to the air.

Photo courtesyGarrett

SeeHow Turbochargers Work for details.
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Increasing your engine's performance is great, but what exactly happens when you turn the

key to start it? The starting system consists of an electric starter motor and a starter

solenoid. When you turn the ignition key, the starter motor spins the engine a few

revolutions so that the combustion process can start. It takes a powerful motor to spin a

cold engine. The starter motor must overcome:

All of the internal friction caused by the piston rings

The compression pressure of any cylinder(s) that happens to be in the compression stroke

The energy needed to open and close valves with the camshaft

All of the "other" things directly attached to the engine, like the water pump, oil pump, alternator, etc.

Because so much energy is needed and because a car uses a 12-volt electrical system, hundreds of amps

ofelectricity must flow into the starter motor. The starter solenoid is essentially a large electronic switch

that can handle that much current. When you turn the ignition key, it activates the solenoid to power the

motor.

Next, we'll look at the engine subsystems that maintain what goes in (oil and fuel) and what comes out

(exhaust and emissions).

What is a Cooling System?

A typical 4 cylinder vehicle cruising along the highway at around 50 miles per hour, will produce 4000

controlled explosions per minute inside the engine as the spark plugs ignite the fuel in each cylinder to

propel the vehicle down the road. Obviously, these explosions produce an enormous amount of heat and,

if not controlled, will destroy an engine in a matter of minutes. Controlling these high temperatures is the

job of the cooling system.

The modern cooling system has not changed much from the cooling systems in the model T back in the

'20s. Oh sure, it has become infinitely more reliable and efficient at doing it's job, but the basic cooling

system still consists of liquid coolant being pumped by a mechanical water pump through the engine, then

out to the radiator to be cooled by the air stream coming through the front grill of the vehicle.

Today's cooling system must maintain the engine at a constant temperature whether the outside air

temperature is 110 degrees Fahrenheit or 10 below zero. If the engine temperature is too low, fuel

economy will suffer and emissions will rise. If the temperature is allowed to get too hot for too long, the

engine will self destruct.

How Does a Cooling System Work?

Actually, there are two types of cooling systems found on motor vehicles: Liquid cooled and Air cooled.

Air cooled engines are found on a few older cars, like the original Volkswagen Beetle, the Chevrolet

Corvair and a few others. Many modern motorcycles still use air cooling, but for the most part,

automobiles and trucks use liquid cooled systems and that is what this article will concentrate on.

The cooling system is made up of the passages inside the engine block and heads, a water pump to

circulate the coolant, a thermostat to control the temperature of the coolant, a radiator to cool the coolant,
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a radiator cap to control the pressure in the system, and some plumbing consisting of

interconnecting hoses to transfer the coolant from the engine to radiator and also to the car's

heater system where hot coolant is used to warm up the vehicle's interior on a cold day.

A cooling system works by sending a liquid coolant through passages in the engine block

and heads. As the coolant flows through these passages, it picks up heat from the engine. The heated

fluid then makes its way through a rubber hose to the radiator in the front of the car. As it flows throughthe thin tubes in the radiator, the hot liquid is cooled by the air stream entering the engine compartment

from the grill in front of the car. Once the fluid is cooled, it returns to the engine to absorb more heat.

The water pump has the job of keeping the fluid moving through this system of plumbing and hidden

passages.

A thermostat is placed between the engine and the radiator to make sure that the coolant stays above a

certain preset temperature. If the coolant temperature falls below this temperature, the thermostat blocks

the coolant flow to the radiator, forcing the fluid instead through a bypass directly back to the engine.

The coolant will continue to circulate like this until it reaches the design temperature, at which point, the

thermostat will open a valve and allow the coolant back through the radiator.

In order to prevent the coolant from boiling, the cooling system is designed to be pressurized. Under

pressure, the boiling point of the coolant is raised considerably. However, too much pressure will cause

hoses and other parts to burst, so a system is needed to relieve pressure if it exceeds a certain point. The

job of maintaining the pressure in the cooling system belongs to the radiator cap. The cap is designed to

release pressure if it reaches the specified upper limit that the system was designed to handle. Prior to the

'70s, the cap would release this extra pressure to the pavement. Since then, a system was added to capture

any released fluid and store it temporarily in a reserve tank. This fluid would then return to the cooling

system after the engine cooled down. This is what is called a closed cooling system.


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The Components of a Cooling System:

1. The Radiator2. Radiator Cooling Fans3. Pressure Cap & Reserve Tank4. Water Pump5. Thermostat6. Bypass System7. Freeze Plugs8. Head Gaskets & Intake Manifold Gaskets9. Heater Core10.Hoses

The Radiator

The radiator core is usually made of flattened aluminum tubes with aluminum strips that zigzag between

the tubes. These fins transfer the heat in the tubes into the air stream to be carried away from the vehicle.

On each end of the radiator core is a tank, usually made of plastic that covers the ends of the radiator,

.

The tanks, whether plastic or brass, each have a large hose connection, one mounted towards the top of

the radiator to let the coolant in, the other mounted at the bottom of the radiator on the other tank to let

the coolant back out. On the top of the radiator is an additional opening that is capped off by the radiator

cap. More on this later.

Another component in the radiator for vehicles with an automatic transmission is a separate tank mounted

inside one of the tanks. Fittings connect this inner tank through steel tubes to the automatic transmission.

Transmission fluid is piped through this tank inside a tank to be cooled by the coolant flowing past itbefore returning the the transmission.
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Radiator Fans

Mounted on the back of the radiator on the side closest to the engine is one or two electric

fans inside a housing that is designed to protect fingers and to direct the air flow. These

fans are there to keep the air flow going through the radiator while the vehicle is going

slow or is stopped with the engine running. If these fans stopped working, every time you came to a stop,

the engine temperature would begin rising. On older systems, the fan was connected to the front of thewater pump and would spin whenever the engine was running because it was driven by a fan belt instead

of an electric motor. In these cases, if a driver would notice the engine begin to run hot in stop and go

driving, the driver might put the car in neutral and rev the engine to turn the fan faster which helped cool

the engine. Racing the engine on a car with a malfunctioning electric fan would only make things worse

because you are producing more heat in the radiator with no fan to cool it off.

The electric fans are controlled by the vehicle's computer. A temperature sensor monitors engine

temperature and sends this information to the computer. The computer determines if the fan should be

turned on and actuates the fan relay if additional air flow through the radiator is necessary.

If the car has air conditioning, there is an additional radiator mounted in front of the normal radiator. This"radiator" is called the air conditioner condenser, which also needs to be cooled by the air flow entering

the engine compartment. You can find out more about the air conditioning condenser by going to our

article onAutomotive Air Conditioning. As long as the air conditioning is turned on, the system will

keep the fan running, even if the engine is not running hot. This is because if there is no air flow through

the air conditioning condenser, the air conditioner will not be able to cool the air entering the interior.

Pressure cap and reserve tank

As coolant gets hot, it expands. Since the cooling system is sealed, this expansion causes an increase in

pressure in the cooling system, which is normal and part of the design. When coolant is under pressure,the temperature where the liquid begins to boil is considerably higher. This pressure, coupled with the

higher boiling point of ethylene glycol, allows the coolant to safely reach temperatures in excess of 250

degrees.

The radiator pressure cap is a simple device that will maintain pressure in the cooling system up to a

certain point. If the pressure builds up higher than the set pressure point, there is a spring loaded valve,

calibrated to the correct Pounds per Square Inch (psi), to release the pressure.

When the cooling system pressure reaches the point where the cap needs to release this excess pressure, a

small amount of coolant is bled off. It could happen during stop and go traffic on an extremely hot day,

or if the cooling system is malfunctioning. If it does release pressure under these conditions, there is asystem in place to capture the released coolant and store it in a plastic tank that is usually not pressurized.

Since there is now less coolant in the system, as the engine cools down a partial vacuum is formed. The

radiator cap on these closed systems has a secondary valve to allow the vacuum in the cooling system to

draw the coolant back into the radiator from the reserve tank (like pulling the plunger back on a

hypodermic needle) There are usually markings on the side of the plastic tank marked Full-Cold, and Full

Hot. When the engine is at normal operating temperature, the coolant in the translucent reserve tank

should be up to the Full-Hot line. After the engine has been sitting for several hours and is cold to the

touch, the coolant should be at the Full-Cold line.
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Water Pump

A water pump is a simple device that will keep the coolant moving as long as the engine is

running. It is usually mounted on the front of the engine and turns whenever the engine is

running. The water pump is driven by the engine through one of the following:

A fan belt that will also be responsible for driving an additional component like an alternator or powersteering pump

A serpentine belt, which also drives the alternator, power steering pump and AC compressor among other

things.

The timing belt that is also responsible for driving one or

more camshafts.

The water pump is made up of a housing, usually made of

cast iron or cast aluminum and an impeller mounted on a

spinning shaft with a pulley attached to the shaft on theoutside of the pump body. A seal keeps fluid from

leaking out of the pump housing past the spinning shaft.

The impeller uses centrifugal force to draw the coolant in

from the lower radiator hose and send it under pressure

into the engine block. There is a gasket to seal the water

pump to the engine block and prevent the flowing coolant

from leaking out where the pump is attached to the block..

Thermostat

The thermostat is simply a valve that measures the temperature of the coolant and, if it is hot enough,

opens to allow the coolant to flow through the radiator. If the coolant is not hot enough, the flow to theradiator is blocked and fluid is directed to a bypass system that allows the coolant to return directly back

to the engine. The bypass system allows the coolant to keep moving through the engine to balance the

temperature and avoid hot spots. Because flow to the radiator is blocked, the engine will reach operating

temperature sooner and, on a cold day, will allow the heater to begin supplying hot air to the interior more

quickly.

The heart of a thermostat is a sealed copper cup that contains wax and a metal pellet. As the thermostat

heats up, the hot wax expands, pushing a piston against spring pressure to open the valve and allow

coolant to circulate.

The thermostat is usually located in the front, top part of the engine in a water outlet housing that also

serves as the connection point for the upper radiator hose. The thermostat housing attaches to the engine,

usually with two bolts and a gasket to seal it against leaks. The gasket is usually made of a heavy paper

or a rubber O ring is used. In some applications, there is no gasket or rubber seal. Instead, a thin bead of

special silicone sealer is squeezed from a tube to form a seal.

Bypass System

This is a passage that allows the coolant to bypass the radiator and return directly back to the engine.

Some engines use a rubber hose, or a fixed steel tube. In other engines, there is a cast in passage built

into the water pump or front housing. In any case, when the thermostat is closed, coolant is directed to


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this bypass and channeled back to the water pump, which sends the coolant back into the

engine without being cooled by the radiator.

Freeze Plugs

When an engine block is manufactured, a special sand is molded to the shape of the coolant passages in

the engine block. This sand sculpture is positioned inside a mold and molten iron or aluminum is pouredto form the engine block. When the casting is cooled, the sand is loosened and removed through holes in

the engine block casting leaving the passages that the coolant flows through. Obviously, if we don't plug

up these holes, the coolant will pour right out.

Plugging these holes is the job of the freeze-out plug. These plugs are steel discs or cups that are press fit

in the holes in the side of the engine block and normally last the life of the engine with no problems. But

there is a reason they are called freeze-out plugs. In the early days, many people used plain water in their

engines, usually after replacing a burst hose or other cooling system repair. "It is summer and I will

replace the water with.

As long as you are good about maintaining the cooling system, you need never worry about these plugsfailing on modern vehicles

Head Gaskets and Intake Manifold Gaskets

All internal combustion engines have an engine block and one or two cylinder heads. The mating

surfaces where the block and head meet are machined flat for a close, precision fit, but no amount of

careful machining will allow them to be completely water tight or be able to hold back combustion gases

from escaping past the mating surfaces.

In order to seal the block to the heads, we use a headgasket. The head gasket has several things it needs to

seal against. The main thing is the combustion pressure

on each cylinder. Oil and coolant must easily flow

between block and head and it is the job of the head

gasket to keep these fluids from leaking out or into the

combustion chamber, or each other for that matter.

A typical head gasket is usually made of soft sheet

metal that is stamped with ridges that surround all leak

points. When the head is placed on the block, the head

gasket is sandwiched between them. Many bolts, calledhead bolts are screwed in and tightened down causing

the head gasket to crush and form a tight seal between

the block and head.

Head gaskets usually fail if the engine overheats for a sustained period of time causing the cylinder head

to warp and release pressure on the head gasket. This is most common on engines with cast aluminum

heads, which are now on just about all modern engines.

Once coolant or combustion gases leak past the head gasket, the gasket material is usually damaged to a

point where it will no longer hold the seal. This causes leaks in several possible areas. For example:


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combustion gases could leak into the coolant passages causing excessive pressure in the

cooling system.

coolant could leak into the combustion chamber causing coolant to escape through the

exhaust system, often causing a white cloud of smoke at the tailpipe.

Other problems such as oil mixing with the coolant or being burned out the exhaust are also possible.

Some engines are more susceptible to head gasket failure than others. I have seen blown head gaskets on

engines that just started to overheat and were running hot for less than 5 minutes. The best advice I can

give is, if the engine shows signs of overheating, find a place to pull over and shut the engine off as

quickly as possible.

Head gaskets themselves are relatively cheap, but it is the labor that's the killer. A typical head gasket

replacement is a several hour job where the top part of the engine must be completely disassembled.

These jobs can easily reach $1,000 or more.

On V type engines, there are two heads, meaning two head gaskets. While the labor won't double if bothhead gaskets need to be replaced, it will probably add a good 30% more labor to replace both. If only one

head gasket has failed, it is usually not necessary to replace both, but it could be added insurance to get

them both done at once.

A head gasket replacement begins with the diagnosis that the head gasket has failed. There is no way for

a technician to know for certain whether there is additional damage to the cylinder head or other

components without first disassembling the engine. All he or she knows is that fluid and/or combustion is

not being contained.

Heater Core

The hot coolant is also used to provide heat to the interior of the vehicle when needed. This is a simple

and straight forward system that includes a heater core, which looks like a small version of a radiator,

connected to the cooling system with a pair of rubber hoses. One hose brings hot coolant from the water

pump to the heater core and the other hose returns the coolant to the top of the engine. There is usually a

heater control valve in one of the hoses to block the flow of coolant into the heater core when maximum

air conditioning is called for.

A fan, called a blower, draws air through the heater core and directs it through the heater ducts to the

interior of the car. Temperature of the heat is regulated by a blend door that mixes cool outside air, or

sometimes air conditioned air with the heated air coming through the heater core. This blend door allowsyou to control the temperature of the air coming into the interior. Other doors allow you to direct the

warm air through the ducts on the floor, the defroster ducts at the base of the windshield, and the air

conditioning ducts located in the instrument panel.

Hoses

There are several rubber hoses that make up the plumbing to connect the components of the cooling

system. The main hoses are called the upper and lower radiator hoses. These two hoses are

approximately 2 inches in diameter and direct coolant between the engine and the radiator. Two

additional hoses, called heater hoses, supply hot coolant from the engine to the heater core. These hoses

are approximately 1 inch in diameter. One of these hoses may have a heater control valve mounted in-

line to block the hot coolant from entering the heater core when the air conditioner is set to max-cool. A


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fifth hose, called the bypass hose, is used to circulate the coolant through the engine,

bypassing the radiator, when the thermostat is closed. Some engines do not use a rubber

hose. Instead, they might use a metal tube or have a built-in passage in the front housing.

These hoses are designed to withstand the pressure inside the cooling system. Because of

this, they are subject to wear and tear and eventually may require replacing as part of routine

maintenance. If the rubber is beginning to look dry and cracked, or becomes soft and spongy, or younotice some ballooning at the ends, it is time to replace them. The main radiator hoses are usually molded

to a shape that is designed to rout the hose around obstacles without kinking. When purchasing

replacements, make sure that they are designed to fit the vehicle.

There is a small rubber hose that runs from the radiator neck to the reserve bottle. This allows coolant

that is released by the pressure cap to be sent to the reserve tank. This rubber hose is about a quarter inch

in diameter and is normally not part of the pressurized system. Once the engine is cool, the coolant is

drawn back to the radiator by the same hose.


1. What is mean of cooling system and ignition system in automobile?2. What do you mean by Lubrication of engine?3. What is difference between coil and magneto ignition system?4. Where are the main components of cooling system?5. Explain the working of ignition system in S.I. Engine?6. What is the purpose of cooling in engine?7. What is the purpose of lubrication in engine?


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OBJECT - To study various types of Boilers and to study Boiler

mounting and accessories.

BOILER:

A boiler is used to generate steam at a desired pressure and temperature by

transferring heat produced by burning fuel to water to change it to steam.

It is a term applied to that device which generates steam at minimum pressure of 3.5

bar having minimum capacity of 22.75 litres.

FIRE TUBE BOILER:

In fire tube boiler, hot gases pass through the tubes and water surrounds them. Heat

from the gases (produced by combustion) is transferred to water, which is thenconverted to steam.

WATER TUBE BOILER:

In water tube boiler, water flows inside the tubes and the hot gases flow outside the tubes.

INDIAN BOILER REGULATION

The Indian Boilers Act was enacted to consolidate and amend the law relating to steam boilers. Indian

Boilers Regulation (IBR) was created in exercise of the powers conferred by section 28

& 29 of the Indian Boilers Act.

IBR Steam Boilers means any closed vessel exceeding 22.75 liters in capacity and which is used

expressively for generating steam under pressure and includes any mounting or other fitting attached

to such vessel, which is wholly, or partly under pressure when the steam is shut off.

IBR Steam Pipe means any pipe through which steam passes from a boiler to a prime mover or other

user or both, if pressure at which steam passes through such pipes exceeds 3.5 kg/cm2 above atmospheric

pressure or such pipe exceeds 254 mm in internal diameter and includes in either case any connected

fitting of a steam pipe.

Boiler Systems

The boiler system comprises of: feed water system, steam system and fuel system. The feed water

system provides water to the boiler and regulates it automatically to meet the steam demand. Various

valves provide access for maintenance and repair. The steam system collects and controls the steam

produced in the boiler. Steam is directed through a piping system to the point of use. Throughout the

system, steam pressure is regulated using valves and checked with steam pressure gauges. The fuel

system includes all equipment used to provide fuel to generate the necessary heat. The equipment

required in the fuel system depends on the type of fuel used in the system. A typical boiler room

schematic is shown in Figure 2.1.


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Figure 2.1 Boiler Room Schematic

The water supplied to the boiler that is converted into steam is called feed water. The two sources of

feed water are: (1) Condensate or condensed steam returned from the processes and (2) Makeup water

(treated raw water) which must come from outside the boiler room and plant processes. For higher boiler

efficiencies, the feed water is preheated by economizer, using the waste heat in the flue gas.

Boiler Types and Classifications

There are virtually infinite numbers of boiler designs but generally they fit into one of two categories:

Fire tube or fire in tube boilers; contain long steel tubes through which the hot gasses from afurnace pass and around which the water to be converted to steam circulates. (Refer Figure 2.2). Fire

tube boilers, typically have a lower initial cost, are more fuel efficient and easier to operate, but they are

limited generally to capacities of 25 tons/hr and pressures of 17.5 kg/cm2.


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.


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Figure 2.2 Fire Tube Boiler

Water tube or water in tube boilers in which the conditions are reversed with the water passingthrough the tubes and the hot gasses passing outside the tubes (see figure 2.3). These boilers can be of

single- or multiple-drum type. These boilers can be built to any steam capacities and pressures, and have

higher efficiencies than fire tube boilers.

Figure 2.3 Water Tube Boiler

Packaged Boiler: The packaged boiler is so called because it comes as a complete package. Once

delivered to site, it requires only the steam, water pipe work, fuel supply and electrical connections

to be made for it to become operational. Package boilers are generally of shell type with fire

tube design so as to achieve high heat transfer rates by both radiation and convection (Refer Figure

2.4).


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Figure 2.4 Packaged Boiler

The features of package boilers are:

Small combustion space and high heat release rate resulting in faster evaporation.

Large number of small diameter tubes leading to good convective heat transfer.

Forced or induced draft systems resulting in good combustion efficiency.

Number of passes resulting in better overall heat transfer.

Higher thermal efficiency levels compared with other boilers.

These boilers are classified based on the number of passes the number of times the hot combustiongases pass through the boiler. The combustion chamber is taken, as the first pass after which there maybe one, two or three sets of fire-tubes. The most common boiler of this class is a three-pass unit with

two sets of fire-tubes and with the exhaust gases exiting through the rear of the boiler.

Boiler mountings and accessories:

Boilers are equipped with two categories of components: boiler mountings and boiler accessories.

Boiler mountings are the machine components that are mounted over the body of the boiler itself for the

safety of the boiler and for complete control of the process of steam generation.

Various boiler mountings are as under:

1) Pressure gauge.

2) Fusible plug.

3) Steam stop valve

4) Feed check valve

5) Blow off cock


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6) Man and mud holes.

1. Pressure gauge:

To record the steam pressure at which the steam is generated in the boiler. A bourden

pressure gauge in its simplest form consists of elliptical elastic tube ABC bent into an arc

of a circle as shown in figure. This bent up tube is called as BOURDENS tube. One end of tube gauge is

fixed and connected to the steam space in the boiler. The other end is connected to a sector through a link.

2. Fusible plug:

To extinguish fire in the event of water level in the boiler shell falling below a certain specified limit.

It protects fire tubes from burning when the level of the water in the water shell falls

abnormally low and the fire tube or crown plate which is normally submerged in the

water, gets exposed to steam space which may not be able to keep it cool. It is installed below boiler's

water level. When the water level in the shell falls below the top of the plug, the steam

cannot keep it cool and the fusible metal melts due to over-heating. Thus the copper

plug drops down and is held within the gunmetal body by the ribs. Thus the steam

space gets communicated to the firebox and extinguishes the fire. Thus damage tofire box which could burn up is avoided. By removing the gun metal plug and copper

plug the fusible plug can be put in position again by interposing the fusible metal

usually lead or a metal alloy.

3. Steam stop valve

A valve is a device that regulates the flow of a fluid (gases, fluidizeds olids, slurries, or liquids) by

opening, closing, or partially obstructing various passageways to shut off or regulate the flow of steam

from the boiler to the steampipe or steam from the steam pipe to the engine.

When the hand wheel is turned, the spindle which is screwed through the nut israised or lowered depending upon the sense of rotation of wheel. The passage for

flow of steam is set on opening of the valve.

4. Feed check valve:

i) To allow the feed water to pass into the boiler.

ii) To prevent the back flow of water from the boiler in the event of the failure of the feed pump.

5. Blow off cock.

To drain out the water from the boiler for internal cleaning, inspection or other purposes.

6. Man and mud holes:

To allow men to enter inside the boiler for inspection and repair. Boiler accessories are those components

which are installed either inside or outside the boiler to increase the efficiency of the plant and to help in

the proper working of the plant. Various boiler accessories are:

1)AirPreheater 2)Economizer 3)Superheater


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Object: Study of various types of Dynamometers.

Theory:

Dynamometer:

dynamometer, "dyno" or "dyn'r" for short, is a machine used to measuretorque androtational speed (rpm)

from whichpowerproduced by anengine,motor or other rotatingprime mover can be calculated.

A dynamometer can also be used to determine the torque and power required to operate a driven machine

such as a pump. In that case, a motoring or driving dynamometer is used. A dynamometer that is designed

to be driven is called an absorption dynamometer. A dynamometer that can either drive or absorb is called

a universal dynamometer.

In the medical realm, hand dynamometers are used for routine screening of grip strength and initial and

ongoing evaluation of patients with hand trauma and dysfunction.

Principles of operation:

An absorbing dynamometer acts as a load that is driven by the prime mover that is under test. The dyno

must be able to operate at any speed, and load the prime mover to any level of torque that the test

requires. A dynamometer is usually equipped with some means of measuring the operating torque and

speed.

The dynamometer must absorb the power developed by the prime mover. The power absorbed by the

dynamometer must generally be dissipated to the ambient air or transferred to cooling water.

Regenerative dynamometers transfer the power to electrical power lines.

Dynamometers can be equipped with a variety of control systems. If the dynamometer has a torque

regulator, it operates at a set torque while the prime mover operates at whatever speed it can attain while

developing the torque that has been set. If the dynamometer has a speed regulator, it develops whatever

torque is necessary to force the prime mover to operate at the set speed.

A motoring dynamometer acts as a motor that drives the equipment under test. It must be able to drive the

equipment at any speed and develop any level of torque that the test requires.Only torque and speed can

be measured;Power must be calculated from the torque and speed figures according to the formula:

Where K is determined by the units of measure used as can be seen below:

To calculate power inhorsepower (hp) use:
http://en.wikipedia.org/wiki/Torquehttp://en.wikipedia.org/wiki/Rotational_speedhttp://en.wikipedia.org/wiki/Revolutions_per_minutehttp://en.wikipedia.org/wiki/Power_(physics)http://en.wikipedia.org/wiki/Heat_enginehttp://en.wikipedia.org/wiki/Motorhttp://en.wikipedia.org/wiki/Prime_moverhttp://en.wikipedia.org/wiki/Power_(physics)http://en.wikipedia.org/wiki/Horsepowerhttp://en.wikipedia.org/wiki/Horsepowerhttp://en.wikipedia.org/wiki/Power_(physics)http://en.wikipedia.org/wiki/Prime_moverhttp://en.wikipedia.org/wiki/Motorhttp://en.wikipedia.org/wiki/Heat_enginehttp://en.wikipedia.org/wiki/Power_(physics)http://en.wikipedia.org/wiki/Revolutions_per_minutehttp://en.wikipedia.org/wiki/Rotational_speedhttp://en.wikipedia.org/wiki/Torque


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where:

Torque is inpound-feet (lbfft)

Rotational speed is inrevolutions per minute (rpm)

To calculate power inkilowatts use:

where:

Torque is innewton-metres (Nm)

Rotational speed is in revolutions per minute (rpm)

(On graphs of torque vs. rpm the numerical values of torque and power are always equal when the rpm

value is equal to the constant, K. The numerical values of horsepower and lbfft of torque are always

equal at 5252 rpm because 5252 rpm in the numerator cancels out the constant, 5252 in the denominator

leaving only the torque figure equal to the power figure.)

Electrical dynamometer setup showing engine, torque measurement arrangement and tachometer

A dynamometer consists of an absorption (or absorber/driver) unit, and usually includes a means for

measuring torque and rotational speed. An absorption unit consists of some type of rotor in a housing.

The rotor is coupled to the engine or other equipment under test and is free to rotate at whatever speed is

required for the test. Some means is provided to develop a braking torque between dynamometer's rotor

and housing. The means for developing torque can be frictional, hydraulic, electromagnetic etc. according

to the type of absorption/driver unit.
http://en.wikipedia.org/wiki/Foot-pound_forcehttp://en.wikipedia.org/wiki/Rotational_speedhttp://en.wikipedia.org/wiki/Revolutions_per_minutehttp://en.wikipedia.org/wiki/Watthttp://en.wikipedia.org/wiki/Torquehttp://en.wikipedia.org/wiki/Newton_metrehttp://en.wikipedia.org/wiki/Image:Dynamometer01CJC.pnghttp://en.wikipedia.org/wiki/Image:Dynamometer01CJC.pnghttp://en.wikipedia.org/wiki/Image:Dynamometer01CJC.pnghttp://en.wikipedia.org/wiki/Newton_metrehttp://en.wikipedia.org/wiki/Torquehttp://en.wikipedia.org/wiki/Watthttp://en.wikipedia.org/wiki/Revolutions_per_minutehttp://en.wikipedia.org/wiki/Rotational_speedhttp://en.wikipedia.org/wiki/Foot-pound_forcehttp://en.wikipedia.org/wiki/Image:Dynamometer01CJC.png


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Types of dynamometers:

In addition to classification as absorption, motoring or universal as described above,

dynamometers can be classified in other ways. A dyno that iscoupled directly to an engine

is known as an engine dyno. A dyno that can measure torque and power delivered by the

power train of a vehicle without removing the engine from the frame of the vehicle, is known as a chassis

dyno.

Dynamometers can also be classified by the type of absorption unit or absorber/driver that they use. Some

units that are capable of absorption only can be combined with a motor to construct an absorber/driver or

universal dynamometer. The following types of absorption/driver units have been used:

Types of absorption/driver unitsWater brake (absorption only)

Fan brake (absorption only)

Electric motor/generator (absorb or drive)

Mechanical friction brake orProny brake (absorption only)

Hydraulicbrake (absorption only)

Eddy current orelectromagnetic brake (absorption only)

1.Water brake dynamometer

Thewater brake dynamometers are very popular, due to their high power capability, controllability, and

relatively low cost compared to other types. The schematic shows the most common type of water brake,

the variable level type. Water is added until the engine is held at a steady rpm against the load. Water is

then kept at that level and replaced by constant draining and refilling, which is needed to carry away the

heat created by absorbing the horsepower (which in itself is a measure of power output of the engine).

The housing attempts to rotate in response to the torque produced but is restrained by the scale or torque

metering cell which measures the torque.
http://en.wikipedia.org/wiki/Couplinghttp://en.wikipedia.org/wiki/Electric_motorhttp://en.wikipedia.org/wiki/Electric_generatorhttp://en.wikipedia.org/wiki/De_Prony_brakehttp://en.wikipedia.org/wiki/Hydraulichttp://en.wikipedia.org/wiki/Electromagnetic_brakehttp://en.wikipedia.org/wiki/Water_brakehttp://en.wikipedia.org/wiki/Water_brakehttp://en.wikipedia.org/wiki/Electromagnetic_brakehttp://en.wikipedia.org/wiki/Hydraulichttp://en.wikipedia.org/wiki/De_Prony_brakehttp://en.wikipedia.org/wiki/Electric_generatorhttp://en.wikipedia.org/wiki/Electric_motorhttp://en.wikipedia.org/wiki/Coupling


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This schematic shows a water brake which is actually a fluid coupling with the housing restrained from

rotating. It is very similar to a water pump with no outlet.

2.Electric motor/generator dynamometer

Electric motor/generator dynamometers are a specialized type of adjustable-speed drives. The

absorption/driver unit can be either an alternating current (AC) motor or a direct current (DC) motor.

Either an AC motor or a DC motor can operate as a generator which is driven by the unit under test or a

motor which drives the unit under test. When equipped with appropriate control units, electric

motor/generator dynamometers can be configured as universal dynamometers. The control unit for an AC

motor is avariable-frequency drive and the control unit for a DC motor is aDC drive. In both cases,regenerative control units can transfer power from the unit under test to the electric utility. Where

permitted, the operator of the

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