ignition, injection, cooling lubrication and governor

8/10/2019 Ignition, Injection, Cooling Lubrication and Governor

1/26

Prof. Santosh B. Bopche 1 Prof. S. A. K. Jilani

RCET BHILAI

UNIT 4

Ignition System, Injection system, Cooling system, Lubrication system and Governing of IC

Engines

University questions:

1) Why cooling of IC engines are essential?

2) Explain the working of a magneto ignition system with the help of neat sketch. Discuss its

relative merits and demerits over battery ignition system.

3)

Describe with the help of suitable sketches i) jerk pump system, ii) common rail system and

iii) distributor system. Discuss their relative advantages and disadvantages.

4) Discuss the functions of lubricant in an engine and describe a typical mist lubrication system

used for a two stroke engine with its advantages and disadvantages.

5) Discuss various methods of control for exhaust emission from petrol engines. (Unit 5)

6) Show by a diagram the energy flow in a reciprocating internal combustion engine.

7) What are the various methods of measuring friction power? Decribe Willians line method.

To which type of engine it is applicable. (The test is applicable only to compression ignition

engines).

8) Explain the terms: i) Quantity governing and ii) Quality governing

9)

Explain why vacuum advance mechanism and centrifugal advance mechanism are necessaryin ignition system. Describe its working with the help of neat sketches.

10) Describe i) Dry sump lubrication system and ii) working of Bosch fuel injection pump, with

the help of neat sketches.

11) Name the various types of liquid cooling system and describe with a sketch the forced

circulation system.

12) What are the main constituents of exhaust emission from petrol engine. Describe with

sketches the following method of petrol exhaust emission control. I) after burner and ii) Catalytic

converter. (Unit 5)

13) Write short notes on: i) Battery ignition system, ii) Wet sump lubrication system, iii) various

methods of governing of IC engines iv) Necessity of engine cooling, v) Fuel injector and its

construction, vi) Liquid cooling of automobile engines, vii) spark plug heat range, viii) working offuel injector, ix) Merits and Demerits of air and water cooling systems, x) Wet sump lubrication

system, xi) Electronic ignition system, xii) Spray penetration and spray direction of injection system,

xiii) Antifreeze mixture, iv) Mist lubrication system.

14) Draw the following performance curves of a SI engine and comment on nature of curve. i)

Indicated power vs speed at full throttle, ii) specific fuel consumption vs speed at full throttle.

15) What is nozzle lip and why is it provided.(Unit 3, Carburettor Qu.)

Answer: It is the difference in the levels of fuel in the float chamber and the fuel-nozzle tip. It is

provided to prevent spilling of fuel in the carburettor during vibration or slight non-horizontal

position of carburettor or during tilting of a vehicle for air filling task, or during aerobic tasks of an

aeroplane (i.e. during take-off or landing of a plane).

16)

Describe Morse test. What is the assumption made in this test? What precautions should betaken in performing this test. (unit 5)

17) Discuss various methods of control for exhaust emission from petrol engines.

18) Draw a typical heat release diagram of diesel engine.

19) Derive an expression for the amount of fuel injected per cycle in terms of brake horse power

and speed of a four stroke diesel engine.

20) Compare the transistorised ignition system with a capacitor discharges system. Highlight the

advantages of each system.

21) What is a flame ionisation detector?

22) Describe the working principle of: i) Bosch smoke meter, ii) Willins line, iii) Light spring

diagram, iv) Inrared gas analyser.

23)

Write the effect of pollution on human health and biosphere.24) Write the advantages and disadvantages of air cooling and water cooling system.

25) Write the operation of wet sump and dry sump lubrication system.


2/26


RCET BHILAI

26) Discuss with circuit diagram of battery ignition system. Write the operation vacuum ignition

advance.

27) Explain the crankcase dilution.

_____________________________________________________________________________

INTRODUCTION:

The function of ignition system is to initiate the flame propagation process at the end of compression

stroke.

The spark must be produced in a repeatable manner e.g., cycle by cycle.

When a spark is produced to ignite a homogeneous air fuel mixture in the combustion chamber of an

engine, it is called the spark ignition system. The ignition systems are classified depending upon

how the primary energyis made available to create a spark, as: i) Battery ignition system and ii)

Magneto ignition system.

REQUIREMENTS OF AN IGNITION SYSTEM:

1. It should provide a good sparkbetween the electrodes of the plugs at the correct timing.

2.

It should function efficientlyover the entire range of engine speed.3.

It should be light, effective and reliable in service.

4. It should be compact and easy to maintain.

5. It should be cheap and convenient to handle.

6. The interference from the high voltage source (waves) should not affect the functioning of

the radio and television receivers inside an automobile.

I. BATTERY IGNITION SYSTEM

Most of the modern SI engines use battery ignition system. In this system the energy required for

producing spark is obtained from a 6 or 12 volt battery.

Practical applications: Passengers cars, light trucks, some motorcycles and large stationary engines

are fitted with battery ignition system. The essential components of the system are:Elements of battery ignition system

1. IGNITION COILIgnition coil is the source of ignition energy in the conventional ignition system. This coil stores the

energy in its magnetic field and delivers it at the appropriate time in the form of a ignition pulse

through the high tension ignition cables to the respective spark plug.

The purpose of the ignition coil is to step up the 6-12 volts of the battery to a high voltage, sufficient

to induce an electric spark across the electrodes of the spark plug.

2. BATTERYTo provide electrical energy for ignition, a storage battery is used. It is charged by a dynamo driven

by the engine. Due to the electro-chemical reactions, it is able to convert the chemical energy intoelectrical energy. Two types of batteries are used for spark ignition engines, the lead acid battery and

the alkaline battery.

3.

CAPACITORThe principle of construction of the ignition capacitor is the same as that of every capacitor, which is

very simple; two metal plates separated by an insulating material- are placed face to face.

4. CONTACT BREAKERThis is a mechanical device for making and braking the primary circuit of the ignition coil. It

consists essentially of a fixed metal point against which, another metal point bears which is being on

a spring leaded pivoted arm. The metal used is invariably one of the hardest metals, usually tungstenand each point has circular flat face of about 3 mm diameter.


3/26


RCET BHILAI

5. DISTRIBUTOR

The function of the distributor is to distribute the ignition surges to the individual spark plugs in the

correct sequence and at the correct instants of time. Depending upon the number of cylinders 4, 6 or

8, there are 4, 6 or 8 ignition pulses generated for every rotation of the distributor shaft. There are

two types of distributors, the brush type and the gap type.

Fig. 1 Battery ignition system

6.

SPARK PLUG

The spark plug provides the two electrodes with a proper gap across which the high potential

discharges to generate a spark and ignite the combustible mixture within the combustion chamber. A

spark plug consists essentially of a steel shell, an insulator and two electrodes. The electrodes are

usually made of high nickel alloy to withstand the severe erosion and corrosion to which they are

subjected in the combustion chamber.

7. BALLAST RESISTOR

A Ballast resistor is provided in series with the primary winding to regulate the primary current. The

objective of this is to prevent injury to the spark coil by overheating if the engine should be operated

for a long time at low speed.

8.

IGNITION SWITCH (Starter key)The function of ignition switch is to turn on or off the ignition system.

OPERATION OF A BATTERY IGNITION SYSTEM

The source of ignition energy in the battery ignition system is the ignition coil. This coil stores the

energy in its magnetic field and delivers it at the instant of ignition (firing point). The ignition coil

consists of two coils (windings), primary and secondary. When the ignition switch is closed, the

primary current flow through the primary winding and induces a magnetic field in the secondary

winding. The condenser does the job of storage and creation of high voltage impulse in the

secondary winding, which assists in production of spark across the terminals of the spark plug. The

distributor distributes the ignition surges across the respective surges, as per the firing order.

II.

MAGNETO IGNITION SYSTEM

Magneto is a special type of ignition system with its own electric generator to provide the necessary

energy for the system. It is mounted on the engine and replaces all the components of the battery


4/26


RCET BHILAI

ignition system except the spark plug. A magneto when rotated by the engine is capable of

producing a very high voltage and does not need battery as a source of external energy.

A special type with its own electric generator to provide energy.

It is mounted on engine & replaces the components of battery ignition system except spark plug.

Very high voltage is produced by rotation of magnet.

It doesnt need a battery as an external source of energy.

Fig. 2 Magneto ignition systemThe working principle of magneto ignition system is exactly same as the battery ignition system.

With the help of a cam the primary circuit flux is changed and a high voltage is produced in the

secondary circuit.

The current generated is low when the cranking speed is low. As the engine speed increases the flowof current also increases. Thus, with the Magneto ignition system there is always a starting difficulty

and sometimes it needs separate battery for starting.

Comparison or difference between Battery and Magneto Ignition system:

Battery Ignition system Magneto Ignition system

Battery is necessary No battery is required

Difficult to start the engine when battery is

discharged.

No battery, no discharge and starting problems

Maintenance problems are more due to battery Maintenance problems are less

The current obtained for primary circuit is

obtained from the battery

The required current is generated by the

magneto

A good spark is available at lower speeds also At low speeds the quality of spark is poorIt occupies more space It occupies lesser space

The efficiency decreases in reduction of spark

intensity as the speed rises

The efficiency improves with increasing

intensity of spark at high speeds

It is employed in cars Mainly used in racing cars

SPARK PLUG HEAT RANGE

The term heat range refers to spark plug thermal characteristics, ability to transfer

combustion heat from its firing end to engine cylinder head.

The plug operating temperatures are governed by amount of heat transfer.

Heat transfer rate depends on the length of heat transfer path & area exposed to thecombustion heat.

A cold running spark plug transfers heat rapidly from its firing end where as hot running

spark plug transfers less heat.


5/26


RCET BHILAI

A cold plug will have a short insulator tip and short heat rejection path.

A Cold spark plug reduces overheating of combustion chamber.

A Cold spark plug is used in heavy duty or racing engines.

A hot plug will have a long insulator tip and long heat rejection path.

Disadvantages of conventional ignition systems (discussed above):

1) Reduction of spark intensity at higher engine speed, (it is due to reduction in time available

to build up the stored energy in the primary circuit, at higher speeds)

2)

Electrical wear and mechanical wear, which demands regular maintenance

3) Short life of breaker points

In order to overcome these disadvantages, modern electronic systems with the use of electronic

circuits came into existence.

MODERN IGNITION SYSTEMS OR ELECTRONIC IGNITION SYSTEM

There are two types of electronic ignitions systems:

1. Transistorized coil ignition system

2. Capacitive discharge ignition system

1.

TRANSISTORIZED COIL IGNITION SYSTEMThese electronic systems are also called high energy electronic ignition systems.

Following are the advantages of electronic ignition system:

a) It reduces the ignition system maintenance

b) It reduces the wear of the components

c) It increases the reliability

d) It extends the life of spark plug

e) It assists the ignition of lean mixture.

The circuit diagram is as shown in Figure 3.

The contact breaker and the cam assembly of the conventional ignition system are replaced by a

magnetic pulse generating system which detects the distributor shaft position and sends electrical

pulse to an electronic control module.The module then switches-off the flow of current to the primary winding, which induces a high

voltage in the secondary winding which is distributed to the spark plugs.

Fig. 3. Transistorized coil ignition system

2. Capacitive discharge ignition (CDI) system

In a capacitor discharge ignition system, a capacitor is used as a means of energy storage. The

ignition transformer (coil) steps up the primary voltage, generated at eh time of spark by the

discharge of the capacitor through the resistor (thyristor, RC), to the high voltage required at thespark plug.


6/26


RCET BHILAI

Fig. 4. Capacitive discharge ignition system (TDI)

The CDI trigger box contains the capacitor, thyristor (RC), power switch, charging device andcontrol unit. The main advantages of CDI system are:

1. The capacitor can store several thousands times more energy per unit of capacitance.

2. The internal resistance is very small, the system is insensitive to side tracking.

3. The breaker points serve as a trigger only. This avoids frequent maintenance and prolongs

contact point life.

4. The current drawn from the magneto is less at low speeds and increase with increase in speed

of the engine. Whereas higher current is drawn at low speeds in electronic ignition systems.

5. The output voltage is relatively independent of engine speed. This eliminates chances of

misfiring of even the fouled spark plugs.

Disadvantage:Because of fast discharging of the capacitor the spark is strong but short. This

can lead to ignition difficulties under rich mixture operation.

FIRING ORDER

The order in which various cylinders of a multi cylinder engine fire is called the firing order.

Four cylinder engine firing orders are

1-3-4-2 or 1-2-4-3 Six cylinder engine firing orders are

1-5-3-6-2-4 or 1-5-4-6-2-3

The main purpose of firing order is: i) to minimize engine vibrations by reducing load on the

bearings, ii) to assist engine cooling and iii) to minimize development of back pressure by exhaust

gases from the exhaust gas manifold.

IGNITION TIMING

To obtain more power ignition timing is required.

Factor affecting it are as

1. Engine speed

2. Mixture strength

3. Part load operation

4. Type of fuel

INJECTION SYSTEM

The fuel injection system is the most vital component in the working of CI engines. Functional requirements of fuel injection system

Accurate metering of the fuel per cycle: The quantity of fuel metered should vary to meet

changing speed and load requirements of the engine.


7/26


RCET BHILAI

Timing the injection of fuel correctly in the cycle so that maximum power is obtained.

Proper control of rate of injection: It is for the desired heat release pattern

Proper atomization of the fuel in to very fine droplets

Proper spray pattern to ensure rapid mixing of the fuel and air

Uniform distribution of fuel droplets throughout the combustion chamber

To supply equal quantities of metered fuel to all cylinders in case of multi-cylinder engines

No lag during beginning and end of injection.

TYPES OF SOLID OR MECHANICAL INJECTION SYSTEM

Individual pump and nozzle system

The details of the individual pump and nozzle system are shown in Fig. (a) and (b). In this

system each cylinder is provided with one pump and one injector. In this arrangement a separate

metering and compression pump is provided for each cylinder. The pump may be placed close to

the cylinder as shown in Fig. (a) or they may be arranged in a cluster as shown in Fig. (b).

Unit injector system

The unit injector system is one in which the pump and the injector nozzle are combined in one

housing. Each cylinder is provided with one of these injectors.

Common rail system( It is used in todays modern four wheelers)

In this system, a HP pump supplies fuel, under high pressure to a common fuel heater. High

pressure in the heater forces the fuel to each of the nozzles located in the cylinders.

Distributor system

In this system, the pump which pressurises the fuel also meters and times it. The fuel pump

supplies metered fuel to a rotating distributor at the correct time.

Fig. 5. Types of solid injection system

FUEL INJECTION PUMP (Bosch)

The main objective of the pump is to deliver accurately the metered quantity of fuel under high

pressure (in the range of 120 to 200 bars). Injection pumps are of two types, 1) Jerk type pump,

2) Distributor type pump.

1) Jerk type pump

It consists of a reciprocating plunger inside a barrel. The plunger is driven by a camshaft. The

working principle of jerk pump is shown in Fig.Fig. (a) A sketch of a typical plunger

Fig. (b) A schematic diagram of the plunger within the barrel. Near the port A fuel is always

available under relatively low pressure. The axial movement of the plunger is through camshaft and


8/26


RCET BHILAI

its rotational movement about its axis is by means of rack D (connected to accelerator of the

vehicle). Port B is the orifice through which fuel is delivered to the injector. It is closed by means

of spring loaded check valve.

When the plunger is below port A, the fuel gets filled in the barrel above it. As the plunger rises and

closed port A the fuel will flow out through port C.

Fig. (c) At this stage rack rotates the plunger and as a result port C also closes. The only escape route

for the fuel is past the check valve through orifice B to the injector. This is the beginning of injection

and also the effective stroke of the plunger.

Fig. (d) The injection continues till the helical indentation (groove) on the plunger uncovers port C.

Now, the fuel will take the easy way out through C and the check valve will close the orifice B. The

fuel injection stops and the effective stroke end. Maximum quantity of fuel in injected for this

plunger position.

Fig. (e) and (f) The plunger is rotated to the position shown. The same sequence of events occurs.

But in this case port C is uncovered sooner. Hence the effective stroke is shortened and minimum

quantity of fuel is injected for this plunger position.

Fig. 6 Bosch Injection fuel Pump


9/26


RCET BHILAI

(Bosch fuel injection pump)

TYPES OF FUEL INJECTOR

Blast injector

Mechanically operated injector

Automatic injector

FUNCTIONS OF NOZZLE

a) Atomization of fuel, b) Proper and uniform distribution of fuel, c) Higher should be the

injection pressure for better dispersion and penetration of the fuel. d) Nozzle design should

be such that fuel is prevented from impinging on the walls. e) Mixing of fuel and air should

be taken care of by the nozzle.

TYPES OF NOZZLE

1. The pintle nozzle

The stem of nozzle valve is extended to from a pin or pintle which protrudes through mouth of

nozzle. It provides a spray operating at low injection pressures of 8 to 10 MPa. Advantage of this

nozzle is such that it avoids weak injection and dribbling. It prevents the carbon deposition on the

nozzle hole.

2. The single nozzle

At the centre of the nozzle body there is a single hole which is closed by the nozzle valve. Major

disadvantage of such nozzle is that it tend to dribble.

3.

The Multi hole nozzleIt consists of number of holes bored in tip of the nozzle. The number of holes varies from 4 to 18 and

the size is from 35 to 200 m. Its advantage lies in the ability to distribute the fuel properly even

with lower air motion available in open combustion chambers.

4. Pintaux nozzle

It is a type of pintle nozzle which has an auxiliary hole drilled in the nozzle body. It injects a small

amount of fuel through this additional hole slightly before the main injection (during low

acceleration or starting condition of the vehicle). The needle valve doer not lift fully at low speeds

and most of the fuel is injected through the auxiliary hole. Main advantage of this nozzle is better

cold starting performance.


10/26


RCET BHILAI

Fig. 7. Types of Nozzles


11/26


RCET BHILAI

Lubrication System: Functions of lubricating system, properties of lubricants. Wet, Dry and

Mist lubrication system.

Lubrication:- It is an art of admitting a lubricant (oil, grease, etc.) between two surfaces thatare in contact and in relative motion to reduce friction and wear between them.

Functions

1. To reduce friction and wear between the moving parts and to increase the life of the engine.2. It reduces friction losses and increases the efficiency of the engine.

3. To provide sealing action of piston rings effectively to reduce the leakage of high pressure

gates from the cylinder to crankcase.

4. To cool the surfaces by carrying away the heat generator in the engine components.

5. To clean the surfaces by washing away carbon and metal particles caused by wear.

6. The lubrication film between two surfaces which are in contact reduces vibrations.

Lubrication of Engine components [which are mainly req.] In I.C. Engine there are many

surfaces in contact which requires lubrication. The principal friction surfaces requires lubrication

are

i. Piston and cylinder,ii. Crankshaft and their bearings,

iii. Crankpin and their bearings,

iv. Wrist pin and their bearings,

v. Value gear.

Lubrication System Types

The different types of lubrication system used in I.C. Engine are:

I. MIST Lubrication System.

II. WET SUMP Lubrication system.

A. The splash system. B. The splash and pressure system

C. The pressure feed system.

III. DRY SUMP Lubrication SystemI MIST Lubrication Systems:

This system is used where crankcase lubrication is not suitable for an engine.

It is used in specially is Two-Stroke Engines. [Because is such engines charge is

compressed is the crank case and not possible to have the lubricating oil in the sump]

In this system, the lubricating oil is mixed with fuel [3% to 6%] and this mixture is

induced into cylinder through carburetor.

The oil in the form of mist goes into the cylinder via the crank case.

The oil which strikes the crankcase walls lubricates the main and connecting rodbearings.

The rest of the oil lubricates the piston, piston rings and the cylinder.

Advantages:1. The system is very simple.

2. The cost is low,

3. It does not require oil pump and filter.

Disadvantages:

1. It gives heavy exhaust smoke due to burning of lubricating oil.

2. It forms carbon deposits on piston crown and exhaust part which effect engine

efficiency and due to which maintenance problems also increases.

3. It increases the corrosion because the oil contacts with acidic vapours produced in

combustion.4. It requires a proper mixing of oil with feed for effective lubrication.

5. It requires some additives to give the oil good mixing characteristics.


12/26


RCET BHILAI

6. During close throttle operation, the engine will suffer from insufficient lubrication as

the supply of fuel is less.

II WET SUMP Lubrication System.

This system contains a pump placed in the oil sump at the bottom of the crankcase of the

engine.

And the pump supplies oil to various engine components.

After lubrication, the oil returns back by gravity and is re-circulated.

A.

Splash System:-

* It is used in light duty engines.

* The lubricating oil is charged into the bottom of the crankcase and maintained at a

predetermined level.

* The oil is pumped to oil (splash) troughs located under the big end of all the

connecting rods and a constant level is maintained.

* A splasher or dipper is provided under each connecting rod cap which dips into the

oil in the trough at every revolution and oil is splashed all over the interior of the

crankcase, into pistons and onto the oil the exposed portions of the cylinder walls.* A hole is drilled through the connecting rod cap through which oil will pass to the

bearing surface.

* Oil pockets are also provided to catch the splashing oil, over main bearings and also

over camshaft bearings.

* From oil pockets the oil will reach the bearing surface through a drilled hole.

* After lubrication the oil return back to sump by gravity and it is cooled by the air and

it is recalculated.

B The splash and pressure lubrication system.

In this system, the lubricating oil is supplied under pressure to main and cam shaftbearings.

Oil is also supplied under pressure to pipes which direct stream of oil against the dipperson the big end of connecting rod bearing cup.

The crankpin bearing are lubricated by the splash or spray of oil thrown up by the dipper.


13/26


14/26


RCET BHILAI

Dry Sump Lubrication System.

In this system, the oil is supplied from an external tank. The oil pump draws oil from the tank and circulates it under pressure to the various

bearings of the engine.

Oil dripping from the cylinders and bearings into sump is removed by a scavenging pumpwhich in turn the oil is passed through a filter and is fed back to the supply tank.

This prevents accumulation of oil in the base of engine.

A filter with a bypass valve is placed in between the scavenging pump and supply tanks.

A separate oil cooler with either water of air as the cooling medium is provided to

remove heat from the oil.

Properties of Lubricants

The lubricants should have the following properties:

i. Suitable viscosity.

ii. Oiliness to ensure less friction and wear and as a protective covering against corrosion.


15/26


RCET BHILAI

iii. High strength to prevent the metal to metal contact and seizure under heavy load.

iv. Should not react with the lubricating surfaces.

v. Should have a low pour point to allow flow of the lubricant at low temperatures to the oil

pump.

vi. No tendency to form deposits by reacting with air water, fuel of the products of combustion.

vii. Should have cleaning ability.

viii. Should have non-foaming characteristics.

ix. Should be nontoxic and non-inflammable.

x. Should be low cost.


16/26


RCET BHILAI

Cooling System:-Cooling System: cooling requirement, air cooling, liquid cooling, type of liquid cooling system,

Advantages and disadvantages of air cooling system, Antifreeze mixture.

Introduction:-Only a part of the total fuel energy supplied to the I.C.E. is converted into useful work. The rest of

energy is rejected as follows.i. Heat from the engine boundaries due to radiation, convection and to a small extent

conduction.

ii. Heat rejected to exhaust gases.

iii. Heat rejected to coolant.

Heat balance for a typical C.I. Engine

Heat to exhaust

Gases (33%)

Heat to

Cooling water (31%)

Heat to F.P

(10%)

Heat supplied Heat to I.P Heat to B.P

(100%) (36%) (26%)

Necessity of Engine cooling:-

1. The lubrication properties of oil depends upon temperature and ability decreases with

increase in temperature. Due to increase in temperature and it might even evaporate and burn

and also damages piston and cylinder surfaces.

2. Due to overheating, the piston may seizure from failure of lubrication.

3. The strength of the materials usually decreases with an increase in temperature. This permitsmaximum operating temperature.

Ex.:- For water cooled Engine; the maximum temperature of cylinder head should not

exceed 270oC and it is 200

oC for an Air cooled engine.

4. The high temperatures in engine results in excusive thermal stresses due to uneven expansion

of various engine parts and may result in cracking.

5. High temperatures in Engine may result in very hot exhaust value which in turn may give rise

to pre ignition and detonation.

6. If the cylinder head temperature is high, the volumetric efficiency and power output of the

Engine is reduced.

Hence to avoid the above problems and to increase efficiency of the engine, the cooling ofengine is necessary.


17/26


18/26


RCET BHILAI

1.Thermo-Syphon Cooling:-

The main principle is that water becomes light on heating.

* The top of the radiator is connected to the top of water jacket by a pipe and bottom is

connected to the bottom.

* Water travels down the radiator across which air is passed to cool it.

* The air flow can take place due to vehicle motion or by a fan.

* The main drawback is cooling depends only on the temperature and is independent of

the engine speed.

* The circulation of water is slow and insufficient and it starts only after the engine has

become not enough to cause thermo-syphon action.

* The radiator should be located above the engine for gravity flow of water.

2. Forced or Pump Systems:-

* In this system a pump is used to cause positive circulation of water in the water jacket

and it is belt driven by the engine.

* The advantage of this system is that the cooling of the engine done under alloperating conditions.

* The water is passed through the radiator where it is cooled by air which is drawn by a

fan and by the air draft due to the forward motion of the vehicle.


19/26


RCET BHILAI

* This system mainly four components a radiator, fan, water pump.

* The main drawback is cooling is insufficient when the vehicle is moving uphill due to

more fuel is burned and coolant circulation is reduced due to declare in speed.

* The cooling system is stopped when engine is not in a running condition, this is

undesirable because cooling must continue till the temperature is reduced to normal.

The cooling is independent of temperature, this may result in overcooling the engine.

3.

Thermostat Cooling [Forced or pump system with thermostat]

This system is similar to forced system except a thermostat which controls the flow of

coolant.* This system overcomes the problem of overcooling of the engine.

* The flow of coolant depends upon cylinder temperature.

* Most of modern cooling systems equipped with a thermostatic device which prevents.

Water from circulating through the radiator for cooling until its temperature has

reached to a value suitable for efficient on operation.

* The thermostat is fitted between the engine and the radiator top.

* A the temperature increases the value is opened to allow coolant to go to the radiator,

when temperature falls the value is closed by passing the water.

* The main advantage is that engine warms up quickly after starting.

* The draw back is there is no method to increase cooling action when engine is very

hot.


20/26


RCET BHILAI

4. Pressurized Water Cooling:-

The boiling point of the coolant can be increased by increasing its pressure. This

allows a greater heat transfer in the radiator due to a large temperature differential.The water pressure is kept between 1.5 bar to 2.0 bar. This system consists of a

vaccum value to avoid formation of vaccum when the water is cooled after engine has

been stopped.

A safety value is also provided so that whenever pressure is relieved; when required.

5. Evaporative Cooling:- [Steam of vapour cooling]

In this system, the cooling water is allowed to reach a temperature of 100oC. This

method of cooling utilizes the high latent heat of vaporization to obtain cooling with

minimum of water.

* The steam formed is flashed off in a separate vessel.

* The make up water so formed is sent back for cooling.

* This system is used for cooling of Industrial Engines.


21/26


RCET BHILAI

Applications of Water Cooling System.

1. W.C.S. is usually used for larger size engines [Cars, buses, etc.]

2.It is used in Industrial applications.

Comparison of Liquid and Air Cooling Systems.

Advantages of Water Cooling

1. High specific output engines have no problem with water cooling with power

required for cooling system.

2. Due to high rate of heat transfer, the size of engine is compact.

3. The fuel consumption of high compressor liquid cooled engines is lower than the air

cooled engines.

4. Even cooling of cylinder barrel and head may be possible.

5. The cooling system can be conveniently located wherever required. This is not

possible in case of ACS.

6. The size of engine does not involve serious problems as for as the design of cooling

system is concerned.

Disadvantages Water Cooling -

1. This is a dependent system in which water circulation in the jackets is to be ensured.

2. Power absorbed by the pump is considerable and its affects the power output.

3. In case of failure of the cooling system serious damage may be caused to the engine.

4. Cost is high.

5. Requires maintenance.

Advantages of Air Cooling-1. Design of engine is simple

2. Absence of cooling pipes, radiator3. No danger of coolant

4. Weight is less as compared to liquid system

5. Installation is easier

6. Engine is not subject to freezing troubles

Disadvantages of Air Cooling-1. Applied to small and medium sized engine

2. Cooling is not uniform

3. Higher working temperature compared to liquid cooling

4. Produce more aerodynamic noise

5. Specific fuel consumption is slightly higher

Anti-freeze Mixture:

These are the chemical substances added to the water in water cooling system to reduce the

freezing point of water and to avoid freezing. They helps in easy starting of engine in cold weather

conditions.

The commonly used anti-freeze materials are Kerosene, Wood Alcohol,

Glycerin, Sugar solution, Calcium or Magnesium Chloride.


22/26


RCET BHILAI

Governing System

Necessity of governing, various methods of governing

Function of Flywheel:The function of a flywheel is to limit the cyclic variations of speed due to fluctuation of

energy.The flywheel stores the energy in the form kinetic energy during power stroke and it delivers

the same to complete the compression and exhaust strokes.

The is not able to control the changes in speed due to variation of load on the engine.

Governor and Function:The speed of the engine increases with decrease in load because the power developed by

engine is same .

The speed can be maintained constant by decreasing the fuel supply or by other means. The

device by which the above can be achieved is calledGovernor

When the fuel supply is decreased by the governor, the speed of the engine will decrease till

the equilibrium is again maintained between the power developed by the engine and new load.

The function of governoris to control the fluctuations of speed the engine within limits withvariation of load from no-load to maximum load on the engine over period of time.

Governing in I.C. Engines:

In S.I. Enginesthe method of governing is simple and usually by throttle governing.

InC.I. Enginesof variable load, the requirement of control of fuel are more demanding since

the engine is required to adjust fuel not only to meet the requirement of load, in addition it needs to

meet the power requirements of variable frictional loads with speed.

The various methods employed for governing of I.C. Engines and they are,

1) Hit and miss governing: In this method the fuel supply is completely cut-off in one or

more number cycles producing an idle stroke.

2) Quality governing: In this method of governing the air-fuel ratio is varied by varying the

mass of fuel to be supplied per cycle as in case of C.I. Engine.

3) Quantity governing: In this method the air-fuel ratio is constant and quantity of mixture

per cycle is varied. This is achieved by the varying the quantity of both air and fuel supply to

the engine as in case of S.I. Engine.

1.

Hit and Miss Governing:The speed of the engine increases with decrease in load because the power developed by

engine is same . In this method the speed is controlled by restricting the combustion process in one

or more number cycles.

In S.I. Engines the gas supply is cut-off while in case of C.I. Engines the fuel supply is cut-

off.

1.1Hit and Miss Governing for S.I. Engines:

When the speed is normal the gas valve is lifted from seat in every stroke and the gas is supplied to

the engine.

The lift of valve is obtained with the help of cam and lever (EFG) arrangement as shown in fig. The

end(E) is lifted once in two revolutions of the crankshaft.


23/26


RCET BHILAI

When the speed of the engine increases beyond the certain limit of mean speed due to

decrease in load on the engines, the balls of the centrifugal governor will fly-out due to increased

centrifugal force, the sleeve (A) lifts in the upward direction.This operates the bell-crank lever(ABC) and its end (C) moves to the right.

It also makes the end(D) to move to the right due to motion of link(CD).

It prevents the lifting of gas valve from its valve seat and the gas supply to the engine is cut-

off. When the speed of the engine drops, the valve is again operated due to the movement of point(D)

to the left consequent to the sleeve movement in the downward direction.

1.2 Hit and Miss Governing for C.I. Engines:

When the shaft rotates, it operates the end (C) of the lever (ABC) once in two revolutions of

the crankshaft.

The other end of the lever(A) connected to pecker piece(R), strikes against the distance

piece(F) which is connected to the fuel pump plunger and fuel is supplied to cylinder.

The operation of fuel injection pump continues up to a certain speed of the engine.

When the speed of the engines exceeds the limiting speed due to reduction in load one the

engine, the balls of the governor fly out due to increased centrifugal force and the sleeve is lifted.

This causes the distance piece to be lifted from its position and pecker piece misses the hit todistance piece making the fuel injection pump to be out of action during that stroke.

When the speed of the engine falls the regular action of fuel supply continues.


24/26


RCET BHILAI

Advantages:

1. Provides better fuel economy at low speeds.

2. System is simple and cheap.

Disadvantages:

1. Engine needs bigger size of flywheel since the fluctuation of energy increases

during the period of omission of power strokes.

2. Engine is subjected to large variations in speed during the cycle.

3.

Engine efficiency is reduced.

Application:

This type of governing is usually employed for small capacity engines upto 20kW and the

engines not requires strict speed variations.

2. Quality Governing:In this method of governing the air-fuel ratio is varied by varying the mass of fuel to be

supplied (mass of air remains constant) according to load on the engine. In other words the air fuel

ratio is changed from cycle to cycle.

In case of C.I. Engines the amount of fuel is varied usually by Spring loaded mechanical

governors or by hydraulic governors.The system may vary the quantity of fuel injected to the cylinder either by varying the stroke

of the fuel pump or it may by-pass part of the fuel back to the fuel tank or it may delay the closing

action of the fuel pump.

2.1 SPRING LOADED MECHANICAL (HARTNELL)GOVERNER:

The spindle of the governor and the yoke receives its rotation from the crankshaft through

gearing.

The governor has two fly balls fixed at the end of vertical arm of a bell-crank lever pivoted

at(A) and (B) mounted on the yoke.

When the engine runs at a certain speed, the centrifugal force exerted by the governor balls is

controlled by the spring force and the sleeve weight.When the engine speed is constant the power developed by the engine equals to the load on

the engine and the governor also rotates at uniform speed.

Working:

Consider a case when the speed of the engine therefore that of the governor increases due to

reduced load on the engine. The governor balls will fly out due to increased centrifugal force.


25/26


RCET BHILAI

The bell crank lever will be actuated about their fulcrums A and B which pushes the sleeve to

move in the upward direction and turns the lever DE such that it reduces the fuel supply to the

engine.

Reverse will be the action of governor if the load on the engine increases from its equilibrium

condition. Increased load will reduce the speed of the governor since the power developed by the

engine would becomes less than the load on the engine.

2.2

Hydraulic Governor:

In order to overcome the disadvantages of the spring loaded governors of supplying low fuel at

reduced load it requires an arrangement to supply an independent source of energy which can

operate the fuel control mechanism.

One method is to supply this energy by the oil under pressure controlled by an oil pump. The

governors using such methods are called hydraulic governors.

Consider a case when the load on the engine falls, the speed on the engine and the governor

increases.

The fly balls fly out due to increased centrifugal force and lifts the sleeve along with the pilot

valve. It allows the oil to flow from power piston via the needle valve and across pipeline to the

oil sump.

It reduces the oil pressure on power piston and the spring B forces this piston to move towardsright which simultaneously operates the fuel control mechanism and reduces the fuel supply to

the engine.

The engine now develops less power and allows the engine and governor speed to reduce.

Disadvantage: It tends to hunt continuously in order to maintain the equilibrium speed.


26/26

RCET BHILAI

3.

Quantity Governing:

In this method of governing the power of the engine is regulated by the quantity of charge which

enters the cylinder.

This is achieved by throttling the charge supplied by the carburetor before entering the

cylinder.

The throttle valve opening and closing is controlled with help of centrifugal governor .This

method is used in static S.I. Engines and gas engines.

In case of automobiles, the throttle valve is either hand operated or by accelerator pedal.

ignition, injection, cooling lubrication and governor

Documents