FMPE Lecture Series Degree: B.Sc. Ag.

(Hons)

Welcome
Course code and name - AENGG 5211, Farm Machinery and Power

LECTURE-04:
Familiarization with different systems of IC engines: Air cleaning system ,
Cooling system, Lubrication system, Fuel supply system and Hydraulic control
system .

Designed and developed by:-

UG Coordinator:
Ranjeet Kumar, RMDCARS Ambikapur
Dr S.V. Jogdand, Professor
Debasish Padhee, BRSMCAE&T Mungeli
AK Shrivastava, CARS Saja Edited by:-
DK Roy, CARS Kawardha Dr. Anoop Kumar Dave,
AK Kerketta, SGCARS Jagdalpur Professor and Head
Familiarization with different systems of IC
engines:

 Air cleaning system

 Cooling system

 Lubrication system

 Fuel supply system and

 Hydraulic control system

Air cleaning system
 Air fuel ratio: 14-15:1
 Unfiltered air may contain millions of
particles of abrasive dust and other matter,
which could cause rapid wear.
 Air cleaning system cleans and filters the air
before entering into the combustion chamber
of the engine.
 The efficiency, performance and durability of
an engine depend mainly upon its cleaner.
Types of air cleaners:
(i) Dry air type and
(ii) Oil bath type air cleaner.
Dry air type air cleaner:
•It contains mainly three main parts, viz. pre-cleaner, main housing
and cleaning element.
•The main housing contains the cleaning element, usually of multi-
wire netting, or of nylon hair or paper.
•Air from the atmosphere enters from the pre-cleaner, passes
through the cleaning element and goes to the inlet manifold.
•The paper filter element is cleaned after 50-100 hours of service.
•Dry air cleaners are mounted (i) vertically in front of the tractor
radiator and (ii) horizontally on the overhead engine.
The following are the advantages of the dry air cleaner:
1. Easy to service.
2. Good performance in gradient and in rough fields.
3. More efficient at high speeds.
4. Straw and chaff cause less restriction to air passage.

Its main disadvantages are:

1. It is costlier to maintain than an oil bath because the filter
elements require replacements very often.
2. Sometimes, dust particles enter the cylinder.
Oil bath type air cleaner:
• In this oil is used for cleaning air.
• This type of air cleaner operates as follows,
air from atmosphere with dust enter the
intake stack, pass down the inlet passage and
impinges upon the surface of the oil, kept in
a container in the lower part of the casing.
The dust particles of the air are trapped and
then the air passes through a wire element.
As the air passes through a screen (filter) the
remaining dirt arrested. The air outlet is on
the side through which the clean air enters
the cylinders.
•In the bottom a removable cup is fitted for
convenient cleaning and servicing.
•Oil bath air cleaners are always mounted
vertically to the engine.
Cooling system:
•fuel is burnt inside the cylinder
•Temperature of the cylinder, piston
and valves raises above 1600 0C
•Because of heat the lubricating oil
also gets oxidized.
•Cooling system is necessary to
maintain the temperature of the
components
•It is estimated that about 40% of
the total heat produced in the
engine cylinder is passed to the
atmosphere by the exhaust gases,
about 30% is used to produce useful
power and rest 30% is to be removed
by cooling system.
Bad effect of high temperature in the engine
• Piston and cylinder may expand to such an extent that the piston
would seize in the cylinder and stop the engine.
• Lubricating quality of the oil inside the cylinder gets deteriorated
due to high temperature.
• Engine knocking as well as loss of power due to pre-ignition of fuel
mixture insides the cylinder.
Purpose of cooling
• To maintain optimum temperature of engine.
• To dissipate surplus heat for protection of engine components like
cylinder, cylinder head, piston, piston rings and valves.
• To maintain the lubricating property of the oil inside the engine
cylinder.
Methods of cooling the engine
• Air cooling
• Water cooling.
Air cooling
• heat is conducted from the
working components of the
engine to the atmosphere directly
using air as a medium.
• Fins are used over the cylinder to
increase the external surface area
of the cylinder.
• The length of these fins is greatest
where the cylinder is the hottest,
particularly near the cylinder head
and will progressively reduce
towards the crank case.
• Air cooling is usually employed for
light vehicles like motorcycle.
Advantages of air cooled engine
• It is simpler in design and construction.
• Water jackets, radiators, water pump, thermostat, pipes, hoses
etc. are eliminated.
• It is more compact.
• It is comparatively lighter in weight.
• Air-cooled engines operate well in both hot and cold climates.
• Air cooling is natural cooling and it is free from corrosive products.
• This system is more reliable and less maintenance is required.
• Air-cooled engines can operate at higher working temperatures
than equivalent liquid cooled.
• Air cooled engines have no coolant leakage (or) problems.
Disadvantages of air cooled engine
• There is uneven cooling of the engine parts.
• Each cylinder has to be cast individually.
• Fins design and casting is difficult.
• Used only in small engines like brush cutter and weeder engines,
portable engines, lawn mower engines, etc.,
Water cooling
• In water cooled engines water or
coolant (heavy water) is used as a
cooling medium.
• The liquid is circulated around the
cylinders in water jacket, to
absorb heat from the cylinder
walls and
• further the heated water is passed
through a radiator which helps in
cooling the water
Types of engine water cooling system:
i. Open jacket or hopper method
ii. Thermosiphon method
iii. Forced circulation method
Open jacket or hopper method
• In this method a hopper or a
jacket is provided around the
engine cylinder in which the
cooling water or coolant is
flowing.
• As long as the hopper contains
water, the engine continues to
operate satisfactorily. As soon as
the water starts boiling, it is
replaced by cold water.
• The hopper is large enough to run
for several hours without refilling.
• A drain plug is provided for
draining water.
• This system is not common in
present days.
Thermosiphon method
• It consists of a radiator, water jacket,
fan and hose connections.
• The system is based on the principle
that heated water which surrounds
the cylinder becomes lighter in
weight and it rises upwards.

• Hot water goes to the radiator, where it passes through tubes surrounded
by air.
• Circulation of water takes place due to the density difference between the
hot water in the engine jacket and cold water in the radiator.
• These two are connected at both sides i.e. at the top and the bottom by
using the hose pipe.
• A fan is driven with the help of a V-belt connected to the crankshaft to suck
air through cells of the radiator unit, resulting in cooling.
• The disadvantage of the system is that circulation of water is greatly
reduced by accumulation of scale or foreign matter in the passage and
consequently it causes overheating of the engine.
Forced Circulation method
• In this method, a water pump is
used to force water from the
radiator to the water jacket of the
engine.
• After circulating in water jacket,
water comes back to the radiator
where it loses its heat.
• To maintain the correct engine
temperature, a thermostat valve is
placed at the outer end of cylinder
head. Cooling liquid is by-passed
through the water jacket of the
engine until the engine attains the
desired temperature. Then
thermostat valve opens and by-
pass is closed, allowing the water
to go to the radiator.
Over heating of engine is mostly due to:

• Accumulation of rust and scale in the radiator and water jacket

• Defective hose pipe

• Defective thermostat

• Defective water pump

• Loose fan belt

Care and maintenance of cooling system
• Clean and fresh water should be filled in the radiator.
• Salt free water should be used in the radiator as far as possible for
prevention of scale formation.
• In cold countries, water in the radiator gets converted into ice and
creates problems in initial starting of the engine. Hence ethyl
alcohol is mixed with water to avoid ice formation.
• Rotten or soft hose pipe should not be used in the system.
• The tension of the fan belt should be checked very frequently. A
loose belt will cause overheating, reduce battery charging and
increases belt wear. If the belt is very tight, it will cause wear on
the pulley of pump and dynamo.
• Oil and grease should always be kept away from the belt. Greasy
belts should be wiped clean.
• The bearing of the water pump should be lubricated regularly.
Care and maintenance of cooling system
• Very hot engines should never be filled with cold water, to avoid
fracture in the cylinder wall and the cylinder head.
• Radiator and water jackets should be flushed out with special air
pressure guns. Radiator can be cleaned by blowing air with
compressor. This process will remove bugs, leaves and dirt from
the radiator.
• The cooling system should be cleaned periodically to remove rust
and scale.
• The radiator cap should not be opened when the engine is hot.

Procedure followed to remove scale from the system is as below

• One kg of washing soda and 0.5 kg of kerosene oil mixed with 10
kg fresh water and the mixture is fed into the radiator and allowed
to remain in the radiator for 8 to 10 hours. After this, the engine is
started and run at medium speed. After 15 to 20 minutes, the
solution is drained out and radiator is flushed with clean water.
Lubrication system
• Internal combustion engines are made up of many moving parts.

• Due to continuous movement of two metallic surfaces over each

other,
– there is continuous wearing of moving parts,
– generation of heat and
– loss of power in the engine.

• To prevent all these harmful effects, the lubrication system is

essential.
Purpose of lubrication
• Reducing the friction: The primary function of the lubrication is to
reduce the friction and wear and tear of the two rubbing parts.
Two rubbing parts always produce friction and continuous friction
produces heat, which causes wearing of the different parts of the
engine and power loss. This friction can be reduced by proper
lubrication. The lubricating oil forms a thin oil film between
moving surface and avoids direct contact. This also reduces noise
produced by the movement of two metal surfaces.
• Cooling effect: The heat generated in piston, cylinder and bearings
is removed by lubricant to a great extent. Thus, lubrication creates
cooling effect on the engine parts and acts as coolant.
• Sealing effect: The lubricant enters into the gap between the
cylinder liner, piston and piston rings. Thus it acts as a seal
preventing the leakage of the gas.
• Cleaning effect: Lubrication keeps the engine parts clean by
removing dirt or carbon from the engine along with the oil.
Types of Lubricants
• There are different types of lubricants such as Solid lubricants
(Graphite, Mica, Talc powder), Liquid lubricants (animal fat oil,
vegetable oil, mineral oil) and Semi solid (Grease).
• The lubricants made of animal fat does not withstand much heat,
it becomes gummy and waxy and hence not suitable for machines.
• Vegetable lubricants are obtained from seeds and plants such as
cotton seed, olive oil, linseed oil and castor oil are used as
lubricant in small machines.
• Mineral lubricants are most popular for engines and machines. It
is obtained from crude petroleum, which is a natural resource.
Mineral lubricants are less expensive.
• Now a days, synthetic oil, which are produced from sand and coal
such as poly alkaline and glycol are also used as lubricants.
Properties of lubricating oil
• Viscosity- It is the property of a lubricant by virtue of which it
offers resistance to flow. The oil should be viscous enough to
maintain a fluid film between the two mating surfaces. The
viscosity is measured by an instrument called viscometer and
expressed in terms of viscosity number. The unit of viscosity in SI
system is Newton-second per square meter (N-s/m2) or Pascal
seconds (Pas). Viscosity is inversely proportional to temperature
i.e., as the temperature increases the viscosity decreases and vice
versa.
• Flash point and Fire point- When the oil is heated, vapors are
released. Flash point is the lowest temperature at which oil is to
be heated until sufficient inflammable vapour come off which
produces a momentary flash when brought to flame. When the
vapours are released continuously and the flame persists for
longer period, then that temperature is called fire point. A good
lubricant has its flash and fire point above the temperature at
which engine work, so that fire hazards are reduced.
Properties of lubricating oil
• Cloud point and Pour point- When lubricating oil is cooled, the
temperature at which wax and other substance in the oil crystallize
and separate out from oil is called cloud point. The lowest
temperature at which the oil ceases to flow when cooled is called
pour point. Cloud point and Pour point indicates the suitability of
lubricant for use in cold conditions. A good lubricant required to give
service at low temperature should possess low pour point and cloud
point.
• Oiliness and Wettability- The ability of the lubricating oil to adhere to
the surface is known as oiliness which depends upon on its
wettability and surface tension. A good lubricant should have oiliness
enough to adhere to the surface even at very high pressure.
• Volatility: A good lubricant should have low volatility at working
temperature.
• Carbon residue: Lubricating oil has higher percentage of carbon in
the combined form. A good lubricant should not deposit carbon
when used at high temperature.
Engine lubrication system
• The lubricating system of an engine is an arrangement of mechanism
which maintains supply of lubricating oil to the rubbing surfaces of
the engine at correct pressure and temperature.
• The engine parts which are to be lubricated are
– internal surfaces of cylinder walls,
– piston pin,
– piston rings,
– crankshaft,
– big and small end of the connecting rod,
– crankpin,
– valve operating mechanism,
– camshaft bearings,
– cooling fan,
– water pump and ignition mechanism.

• There are four method of lubrication systems used in engines:

• - Petro-oil lubrication system.
There are four method of lubrication systems used in engines:
• Petro-oil lubrication system.
• Splash lubrication system
• Forced feed or pressure lubrication system
• Combination of splash and forced feed system
Petro-oil lubrication system
• In this method of lubrication system, about 3 to 6% of the lubricating
oil is mixed with the petrol and fed in to the engine cylinder during
the suction stroke.
• The droplets of the lubricants cause the lubricating effect in the
engine cylinder.
• This method of lubrication is used in small engines like motorcycles
and scooters.
• This method is not much effective in large engines.
• When less lubricating oil is the added, there will be insufficient
lubrication and even result in seizure of the engine.
• If the added oil is more, it will lead to excess exhaust smoke and
carbon deposits in the cylinder exhaust port and spark plugs.
Splash lubrication system
• In this system, the lubricating oil is filled in the sump at the bottom of
the crank case. Scoops/dippers are attached to the big end of the
connecting rod. The pan receives oil supply from the oil sump either
by means of a gear pump or by gravity. The dipper dips into the oil
pan and splashes oil out of the pan. The splashing action of oil
maintains a fog or mist of oil that drenches the inner parts of the
engine such as bearings, cylinder walls, pistons, piston pins, timing
gears etc. The splashed oil then drips back into the sump.
• This system is commonly used in single cylinder engine with closed
crankcase.
• This system is very effective if the oil is clean and undiluted.
Disadvantages of Splash lubrication system
• lubrication is not very uniform and when the rings are worn,
• the oil passes through the piston into combustion chamber, causing
carbon deposition, smoke and spoiling the plugs.
• There is every possibility that oil may become very thin through
crankcase dilution.
• The worn metal, dust and carbon may be collected in the oil chamber
and be carried to different parts of the engine, causing wear and tear.
Forced feed or pressure lubrication system
• The oil is pumped directly to the crankshaft, connecting rod, piston
pin, timing gears and camshaft of the engine. Lubricating oil pump is
a positive displacement pump, gear type or vane type.
• Oil first enters the main gallery, which may be a pipe or a channel in
the crankcase casting.
• From this pipe, it goes to each of the main bearings through holes.
• From main bearings, it goes to big end bearings of connecting rod
through drilled holes in the crankshaft.
• From there, it goes to lubricate the walls, pistons and rings.
• There is separate oil gallery to lubricate timing gears.
• The oil also goes to valve stem and rocker arm shaft under pressure
through an oil gallery.
• The excess oil comes back from the cylinder head to the crankcase.
• This system is commonly used on high speed multi cylinder engine in
tractors, trucks and automobiles.
Combination of splash and forced feed system
• In this system, the engine component, which are subjected to very
heavy load are lubricated under forced pressure, such as main
bearing, connecting rod bearing and camshaft bearing.
• The rest of the parts like cylinder liners, cams, tappets etc. are
lubricated by splashed oil.
Parts of lubrication system
• Oil pump- Oil pump is a positive displacement pump usually a gear
pump, is used to force oil into the oil pipe. The pump is driven by the
camshaft of the engine. The lower end of the pump extends down
into the crankcase which is covered with a screen to check foreign
particles. A portion of the oil is forced to the oil filter and the
remaining oil goes to lubricate various parts of the engine.
• Oil pressure gauge- An oil pressure gauge fitted in the line, indicates
the oil pressure in the lubricating system. About 3 kg/cm2 pressure is
developed in the lubrication system of a tractor engine. If the oil
pressure gauge indicates low pressure in the line, there is some
defect in the system which must be checked immediately.
• Oil filters- Lubricating oil in an engine becomes contaminated with
various materials such as dirt, metal particles and carbon. An oil filter
removes all the dirt. It is a type of strainer using cloth, paper, and
wire screen. Some oil filters can be cleaned by washing but in general
oil filters are replaced by new filters at specified interval. Oil filters
are of two types 1. Full-flow filter 2. By-pass filter
Troubles in lubrication system
• Excessive oil combustion,
• Low oil pressure and
• Excessive oil pressure.

1. Excessive oil consumption: The reasons for excessive oil consumption

are:
(a) More oil goes to combustion chamber and gets burnt - Oil can
enter the combustion chamber through rings and cylinder walls.
(b) Leakage occurs in some part of the line and
(c) Loss of oil in form of vapour through ventilating system.
2. Low oil pressure: Low oil pressure is due to:
(a) Weak relief valve spring
(b) Worn oil pump
(c) Cracked oil line
(d) Obstruction in the oil lines
(e) Very thin oil and
(f) Worn out bearings

Care should be taken to remove these defects as far as possible to

increase the oil pressure in the lubricating system. Sometimes
defective oil pressure indicator shows low oil pressure. This should be
checked.
3. Excessive oil pressure: Excessive oil pressure may result due to:
(a) stuck relief valve
(b) strong valve spring
(c) clogged oil line and
(d) very heavy oil

These defects should be removed to reduce the excessive oil pressure in

the lubricating system. Sometimes defective oil pressure indicator
records high oil pressure. Care should be taken to check this defect.
Care and maintenance of lubrication system
The following care and maintenance should be taken to work lubrication
system properly
1. A good design of oil circulation system should be chosen.
2. Correct grade of lubricant ensures long and trouble free service.
3. Oil should be maintained at desired level in the oil chamber.
4. Oil should be cleaned regularly and after specified period of use,
old filters should be replaced by new filters.
5. Connections, pipes, valves and pressure gauge should be checked
regularly.
6. Oil should be changed regularly after specified interval of time.
Before putting the new oil, the crankcase should be cleaned and
flushed well with a flushing oil.
7. Precautions should be taken to keep the oil free from dust and
water.
Fuel supply system
Fuel is a substance consumed by the engine to produce power. The
common fuel for Internal Combustion engines are
1. Petrol
2. Power kerosene
3. High speed diesel

Quality of fuel
The quality of fuel mainly depends on following properties:
• Volatility of fuel
• Calorific value of fuel
• Ignition quality of fuel
Volatility: Volatility of fuel has considerable effect on the
performance of the engine by affecting the following:
(i) Ease of starting the engine.
(ii) Degree of crankcase oil dilution,
(iii) Formation of vapour lock in the fuel system,
(iv) Accelerating characteristics of the engine,
(v) Distribution of fuel in multi-cylinder engine.

In I. C. engine, all the liquid fuel must be converted into vapour fuel
before burning. High speed diesel oil is most difficult to
vapourise. Vapourising temperature of high speed diesel oil is
higher than that of the petrol, hence the petrol vapourises
quicker than diesel oil in the engine cylinder. This helps in easy
starting of petrol engines.
Calorific value of fuel
• The heat liberated by combustion of a fuel is known as calorific
value or heat value of the fuel. It is expressed in kcal/kg of the
fuel

Sl. No Name of fuel Calorific value, kcal/kg

1 Light Diesel Oil (L.D.O) 10300
2 High speed diesel oil (HSD) 10550
3 Power kerosene 10850
4 Petrol 11100
Ignition quality: Ignition quality refers to ease of burning the oil in the
combustion chamber. Octane number and cetane number are the
measures of ignition quality of the fuel.
(a) Octane number: It is a measure of knock characteristics of a fuel.
The percentage of iso-octane (C8 H18) in the reference fuel consisting
of a mixture of iso-octane and normal heptane (C7H16), when it
produces the same knocking effect as the fuel under test, is called
octane number of the fuel. Iso-octane has excellent antiknock
qualities and is given a rating of 100. Normal heptane would knock
excessively and hence it is assigned a value of zero.
(b) Cetane number: The percentage of cetane in a mixture of cetane
(C16 H34) and alphamethyl naphthelene (C11 H16) that produces the
same knocking effect as the fuel under test is called cetane number
of the fuel. Diesel fuels are rated according to cetane number which
is the indication of ignition quality of the fuel. The higher the cetane
number the better the ignition quality of the diesel fuel. The
commercial diesel fuels have got cetane rating varying from 30 to 60.
• Detonation (Knocking): Detonation or engine knocking refers to
violent noises, heard in an engine, giving a pinging sound during the
process of combustion. It is an undesirable combustion and results in
sudden rise in pressure, a loss of power and overheating of the
engine. It is caused by improper combustion chamber, high
compression pressure, early ignition timing, improper fuel and
inadequate cooling arrangement.

• Pre-ignition: Burning of air-fuel mixture in the combustion chamber

before the piston has reached the top dead centre is called pre-
ignition. Pre-ignition occurs when the charge is fired too far ahead of
the top dead centre of the piston due to excessive spark advance or
excessive heat in the cylinder.
Fuel supply system in spark ignition engine
The fuel supply system of spark ignition engine consists of
1. Fuel tank
2. Sediment bowl
3. Fuel lift pump
4. Carburetor
5. Fuel pipes
In some spark ignition engines the fuel tank is placed above the level of
the carburetor. The fuel flows from fuel tank to the carburetor under
the action of gravity. There are one or two filters between fuel tank
and carburetor. A sediment bowl is also provided to hold the dust and
dirt of the fuel. If the tank is below the level of carburetor, a lift pump
is provided in between the tank and the carburetor for forcing fuel
from tank to the carburetor of the engine. The fuel comes from fuel
tank to sediment bowl and then to the lift pump. From there the fuel
goes to the carburetor through suitable pipes. From carburetor the
fuel goes to the engine cylinder through inlet manifold of the engine.
Carburetor- The process of preparing air-fuel mixture away from the
engine cylinder is called carburetion and the device in which this
process takes is called carburetor.

Functions of carburetor
1. To mix the air and fuel thoroughly.
2. To atomize the fuel.
3. To regulate the air-fuel ratio at different speeds and loads on the
engine.
4. To supply correct amount of mixture at different speeds and loads
Fuel supply system in diesel engine
Fuel supply system of diesel engine consists of following components
1. Fuel tank
2. Fuel lift pump or fuel feed pump
3. Fuel filter
4. Fuel injection pump
5. High pressure pipe
6. Over flow valve
7. Fuel injector
• Fuel tank: It is a storage tank for diesel. A wire gauge strainer is
provided under the cap to prevent foreign particles entering the tank.
• Fuel lift pump: It transfers fuel from fuel tank to inlet gallery of fuel
injection pump.
• Preliminary filter (sediment bowl assembly): This filter is mostly
fitted on fuel lift pump. It prevents foreign materials from reaching
inside the fuel line. It consists of a glass cap with a gasket.
Fuel filter:
• It is a device to remove dirt from fuel oil to ensure trouble free fuel
supply.
• A filter consists of a hollow cylindrical element contained in a shell,
an annular space being left between the shell and the element.
• The filtering element consists of metal gauge in conjunction with
various media such as packed fibres, woven cloth, felt, paper etc.
• These filters are replaced at certain intervals, specified by the
manufacturer.
Mostly two stage filters are used in diesel engines
1. Primary filter 2. Secondary filter.
• Primary filter removes coarse materials, water and dust.
• Secondary filter removes fine dust particles.
Fuel injection pump:
• It is a high pressure pump which supplies fuel to the injectors
according to the firing order of the engine.
• It is used to create pressure varying from 120 kg/cm2 to 300 kg/cm2.
• It supplies the required quantity of fuel to each cylinder at
appropriate time.
• Tractor engines may use two types of fuel injection pump:
(i) Multi-element pump and
(ii) Distributor (Rotary) type pump.
Fuel Injector:
• It is the component, which delivers finely atomised fuel under high
pressure to the combustion chamber of the engine.
• Modern tractor engines use fuel injectors, which have multiple holes.
• Main parts of injector are: nozzle body and needle valve.
• The nozzle body and needle valve are fabricated from alloy steel.
• The needle valve is pressed against a conical seat in the nozzle body
by a spring.
• The injection pressure is adjusted by adjusting the screw.
Fuel supply system in diesel engine
• Fuel is drawn from fuel tank by fuel feed pump and forced to
injection pump through fuel filter.
• The injection pump supplies high pressure fuel to injection nozzles
through delivery valves and high pressure pipes.
• Fuel is injected into the combustion chamber through injection
nozzles.
• The fuel that leaks out from the injection nozzles passes out through
leakage pipe and returns to the fuel tank through the over flow pipe.
• Over flow valve installed at the top of the filter keeps the feed
pressure under specified limit. If the feed pressure exceeds the
specified limit, the over flow valve opens and then the excess fuel
returns to fuel tank through over flow pipe.
Fuel injection system
The system using injectors, fuel injection pump, fuel filter, and fuel lines
for fuel injection is called fuel injection system.
The main functions of fuel injection system are:
(i) To measure the correct amount of fuel required by engine at a
given speed and load,
(ii) To maintain correct timing for beginning and end of injection,
(iii) To inject the fuel into the combustion space against high
compression pressure.
(iv) To atomise the fuel for quick ignition.
Process of fuel injection in diesel engine:
(i) Air injection
(ii) Solid injection.

• Air injection: In this process, the engine uses compressed air to force
the fuel into the cylinder. It is a bulky system and hence it is not
considered very suitable for vehicles and tractors. It is mostly used on
heavy-duty stationary engines.

• Solid injection: A high-pressure pump is used for forcing the fuel into
the combustion chamber.
Ignition system
There are four different systems used for igniting fuel:
(a) Ignition by electric spark i.e. spark ignition
(b) Ignition by heat of compression i.e. compression ignition
(c) Ignition by hot tube or hot bulb and
(d) Ignition by open flame.

• Only the first two are important methods for modern engines.
Spark ignition
• The purpose of spark ignition is to deliver a perfectly timed surge of
electricity across an open spark plug gap in each cylinder at the exact
moment so that the charge may start burning with maximum
efficiency.
• There are two methods in spark ignition:
(a) Battery ignition and
(b) Magneto ignition.
Battery ignition:
Battery ignition system includes two circuits:
(i) Low voltage (primary circuit) and
(ii) high voltage (secondary circuit).

The low-voltage circuit consists of:

(i) battery (ii) ignition switch (iii) a series register (iv) primary winding
and (v) contact breaker. All are connected in series.

The high voltage circuit consists of:

(i) secondary winding (ii) distributor rotor (iii) high voltage wiring and
(iv) spark plugs.
Working of Battery ignition system:
• When the ignition switch is closed, current flows from the battery
through the primary winding of the ignition coil, provided that the
contact breaker points are closed. They produce magnetic field
around the winding.
• When the piston is at the end of compression stroke, the contact
breaker point opens. Thus the flow of current in primary winding
causes the magnetic field to collapse.
• As the field collapses, its lines of force cut the wire turnings of the
secondary winding.
• This increases the voltage across the secondary winding terminals to
a value of 20 to 24 thousand volts.
• The high-voltage surge is delivered to the centre terminal of the
distributor cap where it is picked up by the rotor and directed to the
proper spark plug.
• A spark jumps the plug gap and ignites the compressed air-fuel
mixture.
Hydraulic control system
• It is a mechanism used in a tractor to raise, hold or lower the
mounted or semi-mounted equipments by hydraulic means.

Working principle: The working principle of hydraulic system is based on

Pascal's law. This law states that the pressure applied to an enclosed
fluid is transmitted equally in all directions. Small force acting on
small area can produce higher force on a surface of larger area.
Basic components of hydraulic system
• The basic components are: (i) Hydraulic pump (ii) Hydraulic cylinder
and piston (iii) Hydraulic tank (iv) Control valve (v) Safety valve (vi)
Hose pipe and fittings and (vii) Lifting arms.
Operation:
• The hydraulic pump draws up oil from the oil reservoir and sends it to
the control valve under high pressure.
• From the control valve, the oil goes to the hydraulic cylinder to
operate the piston, which in turn, raises the lift arms.
• The lift arms are attached to the lower link through lift road and the
lower link is attached with implements.
• The hydraulic pump is operated by suitable gears, connected with
engine.