EXPERIMENT NO: Date:
STUDY OF TWO STROKE I.C.ENGINES
After studying this practical, students are able to know
(1) Principles construction & working of 2-S Petrol & Diesel engine.
In this engine, the working cycle is completed in two strokes of the piston or one
revolution of the crank shaft.
In case of two strokes engine, the valves are replaced by ports. Two rows of ports at
different levels are cut in the cylinder walls as shown in fig. These are known as
exhaust ports and transfer ports. In the case of single cylinder engines, a third row of
ports is provided below the first two and these are known as inlet ports.
A specific shape is given to the piston crown as shown in fig Which helps to prevent
loss of incoming fresh charge entering into the engine cylinder through the transfer
port and helps in exhausting only burnt gases.
• The charging of cylinder with air fuel mixture in case of petrol engine or with air in
case of diesel engine, compression of the mixture or air, expansion of gases and
exhausting of the burnt gases from the cylinder are carried out in two strokes.
This can be done by using the following two methods.
1. By using closed crank case compression. In this method crank case works as
an air pump as the piston moves up and down. The charge or air to be
admitted in the cylinder is compressed in crank case, by the pumping action of
underside of piston. This method is known as three channel system & used for
single cylinder small power engines like scooters & motorcycles.
2. A separate pump outside the cylinder is provided to compress the charge or air
before forcing it into the cylinder. This pump is an integral part of an engine &
driven by engine it self. This method of charging is used for large capacity
WORKING OF TWO STROKE PETROL ENGINE:
It will be easier to describe the cycle beginning at the point when the piston
has reached to TDC completing the compression stroke.
The position of the piston at the end of compression as shown in fig.( ). The
spark is produced by spark plug as the piston reaches the TDC (Top Dead Centre).
The pressure and temperature of the gases increases and the gases push the piston
downwards producing power stroke, when the piston downwards producing power
stroke. When the piston uncovers (opens) the exhaust port as shown in fig ( ) during
downward stroke, the expanded burnt gases leave the cylinder through the exhaust
port. A little later, the piston uncovers (opens) the transfer port also as shown in (a).
In this condition the crank case is directly connected to cylinder through port. During
the downward stroke of piston, the charge in crank case is compressed by the
underside of the piston to a pressure of 1-4bar. At this position, as shown in fig.( ),
the compressed charge (fuel & air) is transferred through the transfer port to the
upper port of the cylinder. The exhaust gases are swept out with the help of fresh
charge (scavenging). The piston crown shape helps in this sweeping action as well
as it prevents the loss of fresh charge carried with the exhaust gases. This is
continued until the piston reaches BDC position. During this stroke of piston
(downward stroke) the following processes are completed.
1. Power is developed by the downward movement of piston.
2. The exhaust gases are removed completely from the cylinder by scavenging.
3. The charge is compressed in the crank case with the help of underside of the
As the piston moves upward, it covers transfer ports stopping flow of fresh
charge into the cylinder. A little later, the piston covers exhaust ports and actual
compression of charge begins. This position of piston is shown in fig. The upward
motion of the piston during this stroke lowers the pressure in the crank case below
atmosphere, therefore, a fresh charge is admitted/induced in the crank case through
the inlet port as they are uncovered by the piston.
The compression of charge is continued until the piston reaches its original position
(TDC) and the cycle is completed.
In this stroke of the piston, the following processes are completed.
1. Partly scavenging takes place as the piston moves from BDC to position shown in
2. The fresh charge is sucked in the crank case through the Carburettor.
3. Compression of charge is completed as the piston moves from the position shown
in fig.( ) to TDC as shown in fig.( ).
The cycle of engine is completed within two strokes of the piston.
WORKING OF TWO STROKE DIESEL ENGINE:
As the piston moves down on the power stroke, it first uncovers the exhaust
port, and the cylinder pressure drops to atmospheric pressure as the products of
combustion come out from the cylinder. Further downward movement of the piston
uncovers the transfer port (TP) and slightly compressed air enters the engine cylinder
from the crank case. Due to deflector on the top of the piston, the air will move up to
the top of the cylinder and expels out the remaining exhaust gases through the
exhaust port (EP).
During the upward movement of the piston, first the transfer port and then the
exhaust port closes. As soon as the exhaust port closes the compression of the air
starts. As the piston moves up, the pressure in the crank case decreases so that the
fresh air is drawn into the crank case through the open inlet port as shown in fig. Just
before the end of compression stroke the fuel is forced under pressure in the form of
fine spray into the engine cylinder through the nozzle into this hot air. At this moment
the temperature of the compressed air is high enough to ignite the fuel. It suddenly
increases the pressure and temperature of the products of combustion. The rate of
fuel injection is such as to maintain the gas pressure constant during the combustion
period. Due to increased pressure the piston is pushed down with a great force. Then
the hot products of combustion expand. During expansion some of the heat energy
produced is transformed into mechanical work. When the piston is near the bottom of
the stroke it uncovers exhaust port which permits the gases to flow out of the
cylinder. This completes the cycle and the engine cylinder is ready to suck the air
Answer the following questions:
(1) What is crankcase compression? Explain?
(2) Write function of deflector?
(3) When piston moves from TDC to BDC which strokes are performed? When piston
moves from BDC to TDC which strokes are performed?
(4) Explain working of any two stroke with diagram?
(5) Compare 4-S cycle engine & 2-S cycle engine?
(6) Why 4-S cycle engine is having more efficiency than two stroke cycle engine?
(7) Why 2-S cycle engine develops approximately double power than 4-S cycle
(8) Why 4-S cycle engine requires more maintenance?
EXPERIMENT NO: Date:
STUDY OF FOUR STROKE I.C.ENGINES
After Studying this practical students are able to know
(1) Principles construction & working of 4-S Petrol & Diesel engine.
Any I.C.Engine works on particular cycle and in any I.C.Engines a cycle comprises of
four basic operations viz. Suction, compression, expansion and exhaust. If all these
four basic operations are performed / completed in four strokes of piston or two
revolutions of crank shaft, the engine is called four stroke engines. It may be petrol
engine or diesel engine, depending upon type of fuel used. In this there will be one
power stroke in two revolution of crank shaft / four strokes of piston.
• Valves are used to induct the charges into the cylinder and to push out the
exhaust gases from the cylinder.
• Valves are actuated by cam & cam shaft mechanism. To open valve, the moment
is transferred in this sequence: cam shaft-cam-follower-push rod-rocker arm.
• Overall efficiency of 4-Stroke engines is more than 2-Stroke engines.
• The speed of cam shaft is half than crank shaft speed. (e.g. if engine is running at
1000 RPM, camshaft speed will be 500 RPM.)
Now we will study the basic four operations executed in cylinder to complete the
4-STROKE PETROL ENGINE
The working cycle of the engine is completed in four strokes or in two revolutions of
crank and petrol is used as fuel.
Suction stroke: The piston is at the top most position
(TDC) and is ready to move down wards the mixture of
fuel (petrol) and air. The inlet valve is open and
exhaust valve is closed. As the piston moves
downwards, a fresh charge of fuel and air mixture
enters the cylinder through inlet valve due to suction
created. This continues until piston reaches BDC. At
this position inlet valve closes. This downward
movement of piston is known as suction stroke & crank
rotates by 80 during this period.
Compression stroke: During this stroke, both valves
(inlet and exhaust) are closed and piston moves
upward and compresses the charge enclosed in the
cylinder. The pressure and temperature of mixture
increases continuously, during this process. As the
piston reaches, the top dead centre (TDC). Position,
the mixture is ignited by an electric spark. The burning
of mixture is more or less instantaneous and pressure
& temperature of gases increases while the volume
Power stroke or Expansion stroke: During the
expansion stroke, both the valves remain closed. The
high pressure and temperature gases push the piston
downwards and the gas pressure gradually decreases.
During this stroke, piston moves from TDC to BDC.
This stroke is known as power stroke, as work is done
during this stroke. The exhaust valve opens as the
piston reaches BDC position and pressure falls
suddenly to atmospheric pressure at constant volume.
Exhaust stroke: During upward motion of the piston
the exhaust valve is open and inlet valve is closed. The
piston moves up in cylinder pushing out the burnt
gases through the exhaust valve. As the piston reaches
the TDC, again inlet valve opens and fresh charge is
taken in during next downward movement of the piston
and cycle is repeated.
Working of 4-Stroke Diesel Engine
All working operations such as suction, compression, expansion and
exhaust are completed in 4-strokes of piston or two revolutions of crankshaft and
diesel is used as fuel. Therefore it is known as 4-stroke diesel engine. The liquid fuel
like diesel, which cannot be vaporized, is injected into the engine cylinder in the form
of fine spray with the help of fuel pump and injector. The working of the 4-stroke
diesel engine is described as given below.
(1) Suction Stroke :
The inlet valve remains open
during this operation. The air is taken in
through the inlet valve as the piston moves
from Top Dead Center (TDC) to Bottom
Dead Center (BDC).
(2) Compression Stroke :
During this stroke, the inlet
and exhaust valves remain closed. The
piston moves from BDC to TDC and
compresses the air, taken in during suction
stroke, with an increase in pressure and
temperature and decrease in volume.
(3) Expansion Stroke :
Just before completing the
compression stroke, the fuel injector opens
and injects the diesel fuel in the form of fine
spray inside the cylinder. The injected fuel
starts burning due to the high temperature
inside the cylinder, as compression ratio of
diesel engine is high. The supply of fuel is
cut-off after some part of the expansion
stroke, and the hot gases expand pushing
the piston towards BDC. During this stroke,
the piston moves from TDC to BDC. At the
end of the stroke exhaust valve opens and
the pressure inside the cylinder falls to
(4) Exhaust Stroke :
The hot gases in the cylinder
are driven out through exhaust valve from
the cylinder as the piston move from BDC to
TDC. The exhaust valve is closed at the end
of the stroke. Again the inlet valve opens and
the same operations are repeated.
Answer the following questions.
(1) Why four stroke engines is called four stroke?
(2) Write position of valve during each stroke of 4-S cycle engine?
(3) Write ratio of rotation of cam shaft to crank shaft? Why?
(4) Explain any two stroke of 4-S IC Engine?
Experiment No: Date:
STUDY OF AIR COMPRESSOR
After studying this practical, students will be able to know
(1) Use of air compressor
(2) Classifications of compressor
(3) Basic terminology of compressor.
(4) Principle construction & working of following air compressor.
• Reciprocating compressor
• Rotary compressor
Axial Flow compressor
Vane type blower
A compressor is a device, which receives gas or vapour, increases its pressure and
delivers it at a high pressure.
Use of compressed air:
Compressed air is used as motive power in the operation of drills, hammers, hoist
sand blasters, controls, air brakes, sprays, chucks, lift gates etc. Air compression is a
major factor in performance of I.C.engines and gas turbines. Compression of vapour
is met with in many refrigeration plants.
Classification of compressors:
The compressors are broadly classified as positive displacement compressors or
rotary compressors. Positive displacement compressors includes, reciprocating
compressors and compression blowers while later includes radial flow or centrifugal
compressors. Axial flow compressors and Mixed flow compressors. Any one of these
compressors may be compounded in series to increase pressure range or may be
compounded in parallel to increase the capacity.
Air compressor terminology:
(1) Single acting compressors are those compressors in which suction compression
and delivery of air take place on one side of the piston.
(2) Double acting compressors are those compressors in which suction, compression
and delivery take place on both side of the piston.
(3) Single stage compressors are those compressors in which the compression of air
from the initial pressure to final pressure is carried out in one cylinder only.
(4) Multi-stage compressors are those in which the compression of air from initial
pressure to the final pressure is carried out in more than one cylinder.
(5) Ratio of Compression is defined as the ratio of absolute discharge pressure to
absolute intake pressure.
(6) Volumetric efficiency is the ratio of actual capacity of compression to its
The reciprocating air compressors:
It consists of a piston that operates in a cylinder driven through a connecting rod and
crank mounted on crank mounted on crankcase. There are inlet and delivery valves
mounted on the head of cylinder.
These valves are usually of the pressure differential type, meaning that they will
operate as a result of the difference of pressure across the valve. The operation of
this type of compressor is as follows.
When the piston is moving down the cylinder, any residual compressed air left in the
cylinder after the previous compression will expand and will eventually reach a
pressure slightly below intake pressure early on in the stroke. This means that the
pressure outside the inlet valve is now higher than on the inside and hence the inlet
valve will lift off its seat. Thus a fresh charge of air will be aspirated into the cylinder
for the remainder of the induction stroke as it is called. During this stroke the delivery
valve will remain closed, since the compressed air on the outside of this valve is at a
much higher pressure. The piston is now moving upwards. At the beginning of this
upward stroke, slight increase in cylinder pressure will have closed the inlet valve
since both the inlet and outlet valves are now closed the pressure of the air will
rapidly rise because it is now locked up in the cylinder. Eventually a pressure will be
reached which is slightly in excess of the compressed air on the outside of the
delivery valve and hence the delivery valve will lift. The compressed air is now
delivered from the cylinder for the stroke. At the end of compression stroke the piston
once again begins to move down the cylinder, the delivery valve closes, the inlet
valve eventually opens and the cycle is repeated.
ROTARY AIR COMPRESSORS:
There are three basic types of rotary air compressors, namely, the radial or
centrifugal compressors, the axial flow compressors, and blower.
NON POSITIVE DISPLACEMENT COMPRESSOR
Radial compressor consists of impeller rotating usually at high speed (something
like, 20,000 to 30,000 rpm in some cases) in a casing. The impeller consists of disc
onto which radial blades are attached. The blades break up the air into cell. If the
impeller is rotated the cells of air will also be rotated with the impeller. Centrifugal
force will then come in to action and thus the air in the cells will move out from the
outside edge of the impeller and more will move into centre of the impeller to take its
place. The centre is called the eye of impeller. The air as it moves away from the
outside edge of impeller passes into a diffuser ring, which helps to direct the air into
the volute. Also, in the diffuser ring the air is decelerated, the deceleration producing
a pressure rise in air.
The volute is a collecting device for this compressor and it will be noticed that its
cross-section increases round the compressor. The reason for this is that as the air is
collected round the volute, so a greater section will be required to pass the increasing
quantity of air. This type of compressor is a continuous flow device and will deal with
large quantities of air through a moderate pressure range. Pressure compression
ratios of 4:1 to 6:1 are common.
Axial Flow Compressor:-
In axial type of compressor there are alternate rows of fixed and moving blades.
The fixed blades are fixed in an outer casing while the moving blade are fixed to a
central drum which can be rotated by means of a drive shaft. The moving blade can
be locked at in a simple way as a set of fans in series. These blades progress the air
through the compressor, the fan before, boosting the fan after, as it were. The fixed
blades act both as guide vanes and diffusers. The angles of all blade rows are set
such that there is a smooth progression of air from blade row to blade row. The air
passes axially along the compressor, hence its name. Air is removed by suitable duct
at the end of the compressor. Once again, this type of compressor is high speed and
in general, deals with large quantities of air. Pressure compression ratio of 10:1 or
more can be obtained. This compressor design is commonly used in aircraft gas
(b) Working: The compression is performed in a similar manner to that of the
centrifugal type. The work input to the rotor shaft to the air is by the moving blades.
This will accelerate the air. The velocity of the air relative to the blades is decreased
as the air passes through them because of the space provided between blades. This
reduction in velocity increases the arranged to form diffuser passages. The fixed
stator blades guide the air by changing its angle in order to enter the second row of
moving rotor blades. The numbers of stages are usually large.
These compressors are capable of developing pressure ratios of 1.2 to 1.3 per stage.
These compressors can develop pressure up to 8bar and deliver 1 to 5 m3
/s of air.
Thus, in order to achieve above pressure ratio of 8 about 6 stages are required.
POSITIVE DISPLACEMENT COMPRESSOR:
The two-lobe type roots
blower is shown in fig. For higher-
pressure ratios, three and four
lobe versions are in use.
One of the rotors is
connected to the drive. The
second rotor is gear driven from
the first. Thus both the rotors
rotate in phase. In order to seal
delivery side from the inlet side,
the profile of the lobs is of
cycloidal or involute. This scaling
continues until delivery
To reduce wear, there must be some clearance between the lobes and between the casing
and the lobes. Although this clearance will form a leakage path for compressed air and will
have an adverse effect on efficiency when pressure ratio increases.
In order to achieve the acceptable efficiency of the blower, a very small clearance of about
0.2 to 0.5 mm is provided. The pressure at the delivery is not constant. Single acting blower
can develop the pressure up to twice the inlet pressure.
(b) Principle of Operation:
The operation can be considered as talking place in two distinct phases suction
and discharge as described below
The rotation of the rotors
produces a space, which increases
the volume as rotation continues. The
gas therefore flows into the machine
to fill the space
The flow of gas into the blower
continues involving both the rotors.
A quantity of gas is trapped
between one rotor and the casing for
a very brief interval. This part of the
blower is not open to the suction. No
gas flows into it. The gas continues to
flow into the space produced by the
rotation of the other rotor. This rotor is
carrying out the same cycle as the
first but 90o
The trapped volume is at
suction pressure as it has simply
been drawn in by the movement of
the rotors. There is no internal
compression of gas as there is no
meshing of rotors prior to the release
to discharge. Continued rotation of
rotors opens the trapped space to the
As the pressure in the
discharge port is higher than suction
pressure, the movement that the
trapped volume opens to the
discharge port, a back flow of gas
from discharge takes place. This will
increase its pressure up to discharge
level. The continued rotation then
pushes out the gas in the chamber
Summery of Principles of operation:
1. A root blower has only two moving parts, the two rotors, which are normally
identical in shape and size.
2. Operation is entirely rotary
3. As the rotors are symmetric about their centre of rotation, the operation is
dynamically in balance.
4. Suction takes place at one side of the rotors and discharge at the other.
5. Discharge of the compressed gas is complete and there is no clearance
6. The operation is positive displacement as the gas is drawn in, trapped and
discharged by the movement of the components.
VANE TYPE COMPRESSOR OR BLOWER:
(a) Construction: Fig shows this type of compressor.
It consists of a rotor mounted eccentrically in the body. This rotor is supported by
ball and roller bearings in the end cover of the body. The rotor is slotted to take
the blades. These blades are made from non-metallic material usually fiber. The
casing of the compressor is circular in which the drum rotates during rotation. The
vanes remain in contact with the casing. The slots in which the blades are fixed
are cut radially into the rotor. The blades or vanes can slide in and out due to the
centrifugal forces setup by the rotary motion of the rotor. The circular casing is
provided with one inlet and one outlet port. The space between the rotor and its
casing is subdivided into a number of compartments by these vanes. Two
consecutive vanes form one compartment. Due to eccentric motion of the rotor
the volume of each compartment keeps on changing. It can develop the pressure
up to 9bar and delivered 15 m3
/min of air.
(b) Principle of Operation:
The operation can be considered to take place in three phases. Suction internal
compression and discharge.
(1) Suction phase:
The relative position of the
rotor and the casing is clearly shown
in fig. The start of the suction phase
is indicated for one space between
two of the vanes. The rotation of the
rotor causes space to be formatted
between the vanes, the rotor and
casing. This space is connected to
the suction port so that gas from the
suction passes into the space to fill it.
The continued rotation of the
rotor increases the space open to the
suction. Hence more gas flows in, to
fill it. This process continues until the
space into which the gas is flowing
stops increasing. This will depends
on the number of vanes in the
After this point the enclosed
volume starts to reduce if it is still
connected to the compressor suction
gas will be dispelled. The suction port
is positioned to be cut off as soon as
the vanes move beyond this point.
Internal Compression Phase:
The reduction in volume which
occurs due to continued rotation thus
causes internal compression to take
place. This will continue until the
leading vane moves over the
discharge port. This will allow the
trapped gas to be released. The
positioning of the discharge port
determines the amount of internal
It is the final phase of
operation. When the leading vane
passes the discharge port, the gas is
open to discharge and is expelled.
Write answers for following questions:
1. Write use of air compressor.
2. Classify air compressor.
3. Differentiate single stage compressor & multistage compressor.
4. Valves of reciprocating compressor works on which principle? How?
5. Why cross section of volute increases round the compressor?
6. Why axial flow compressor is called axial flow?
7. Due to which process pressure rise takes place in roots blower? Briefly
8. What you understand by positive displacement type compressor?
9. Why rotor of vane type blower is eccentrically mounted?
10.Due to which two processes pressure rise takes place in vane type blower?
EXPERIMENT NO: Date:
STUDY OF SIMPLE CARBURETTOR OF PETROL ENGINE
After studying this practical, students are able to know……
(1) Carburetion process
(2) Function of Carburettor.
(3) Construction & working of simple Carburettor.
(4) Limitations of simple carburetor.
In petrol engines, the air and fuel is mixed outside the engine and partly
evaporated mixture is supplied to the engine. The fuels such as petrol, benzol and
alcohol used in S.I. engine vaporizes easily if injected in the flow of air, therefore, the
engine suction is sufficient to create the air flow and fuel injected easily evaporates.
The oil fuels which are used in C.I.engines do not vaporize easily. Therefore, a
separate injection system is used. The process of preparing air-fuel mixture in
S.I.engine outside the engine cylinder is known as Carburetion. The device used for
this purpose is known as Carburettor.
During the suction, the air is sucked as vacuum is created inside the engine
cylinder. The fuel is injected in the air from the Carburettor and a mixture is supplied
to the engine cylinder. It is desirable to have a complete vaporized mixture in the
engine cylinder but some of the larger droplets may reach the cylinder in the form of
liquid and they are mixed and vaporized during the compression stroke. The time
available for atomization, mixing and vaporisation is so small, (0.02 second when
engine is running at 3000 RPM) the design of the system becomes more difficult.
Temperature is one of the factors which accelerates vaporization but this would
reduce the power output due to reduction is mass flow.
Carburettor is a device, which is used for atomizing and vaporizing the fuel
(petrol) and mixing it with the air in varying proportions, to suit the changing operating
conditions of the engine.
Atomization is the breaking up the liquid fuel (petrol) into very small particles
so that it is properly mixed with the air. But vaporization is the change of state of the
fuel from liquid to vapor. Carburettor performs both the process i.e., atomization of
the fuel and vaporization of the fuel.
Fig. (A)shows a simple Carburettor, which consists of, (a) float and float
chamber, (b) venturi and throttle valves and (c) choke valve.
Float and float chamber:
The petrol is supplied to the float chamber from the fuel tank through the filter
and fuel pump. The arrangement in float chamber is such that when the petrol
reaches a particular level, the needle valve blocks the inlet passage and thus cuts off
the petrol supply. On the fall of the petrol level in the float chamber, the float
descends down and inlet passage opens. The petrol is supplied to the chamber
again. Thus a constant fuel (petrol) level is maintained in the float chamber. The float
chamber is vented to atmosphere. The level of fuel float chamber is kept slightly
below the top of the jet to prevent the leakage when not operating. The difference of
level between the top of the jet and the source of the fuel in the float chamber is
usually kept as 1.5 mm.
Venturi and throttle valve:
The main body of the Carburettor consists of a narrower passage at its centre.
This narrower passage is known as venturi. One end of the Carburettor is mounted
on the intake manifold of the engine. During the suction stroke of the piston, vacuum
is created in the cylinder of the engine. Due to vacuum, the air is drawn through the
Carburettor. The velocity of the air increases as it passes through the venturi where
the area of cross section is minimum. Due to increased velocity of air at the venturi,
the pressure at the venturi decreases. Therefore a low-pressure zone is created in
the ventruri. The outlet of the discharged jet which is located at the venturi is in the
zone of low pressure. The fuel issues out from the nozzle in the form of fine spray.
This fuel spray is mixed with air in the mixture chamber and then the mixture is
supplied to the intake manifold of the engine. The throttle valve is placed between the
mixing chamber and the intake manifold of the engine. The supply of the mixture is
controlled by means of throttle valve.
During starting or warm up in cold weather the engine requires extra rich
mixture. This is done by introducing a choke valve in the air passage before the
venturi. For this purpose the choke valve is closed to allow only a limited supply of air
and creates high vacuum near the fuel jet. The fuel flow increases as the vacuum
near the jet increases. This enriches the mixture as desired.
During suction stroke air is drawn through the venturi. Venturi is a tube of
decreasing cross-section, which reaches a minimum at throat. (Venturi tube is also
known as choke tube and is so shaped that it gives minimum resistance to air flow.)
The air passing through the venturi increases in velocity and the pressure in the
venturi throat decreases. From the float chamber, the fuel is fed to discharge jet, the
tip of which is located in the throat of the venturi. Now because the pressure in the
float chamber is atmospheric and that at the discharge jet is below atmospheric, a
pressure differential, called Carburettor depression, exits which causes the discharge
of fuel into the air stream and the rate of the flow is controlled or metered by the size
of smallest section in the fuel passage. (This is provided by the discharged jet and
the size of this jet is chosen empirically to give the required engine performance).
The pressure at the throat at the fully open throttled condition lies between 4 and 5
cm Hg below atmospheric, and seldom exceeds 8 cm Hg below atmospheric. To
avoid wastage of fuel, the level of the liquid in the jet is adjusted by the float chamber
needle valve to maintain the level a short distance below the tip of the discharge jet.
The petrol engine is quantity governed which means that when less power is
required at a particular speed the amount of charge delivered to the cylinders is
reduced. This is achieved by means of throttle valve of the butterfly type which is
situated after venturi tube. As the throttle is closed less air flows through the venturi
tube and less quantity of air-fuel mixture delivered to the cylinders and hence less is
the power developed. As the throttle is opened, more air flow through the choke tube,
and the power of the engine increases.
A simple Carburettor of the type described above suffers from a fundamental
fault in that it provides increasing richness as the engine speed and air flow
increases with full throttle because the density of the air tends to decrease as the
rate of air flow increases. Also it provides too lean mixture at low speed and part
Limitations of a Simple Carburettor:
(a) A simple Carburettor is suitable only for engines running at constant speeds and
at constant load condition as it gives proper mixture at only one engine speed and
(b) The working of the simple Carburettor is, effected by changes of atmospheric
temperature and pressure.
(c) Simple Carburettor does not have arrangements for providing rich mixture during
starting and warm up.
(d)It cannot provide very rich mixture required for sudden acceleration of the engine.
(1) Why a separate ignition system is used for diesel engine?
(2) Define carburetion process?
(3) Write function of Carburettor? Explain atomization & vaporization?
(4) Write function of needle valve, throttle valve & choke valve?
(5) Why the level of petrol in float chamber is kept slightly lower than the top of jet?
(6) What is ventury? Which pressure act at throat of ventury? How?
FILL IN THE BLANK:
1. Theoretical air-fuel ratio required for complete combustion is __________. (20:1,
2. The throttle valve is used to control __________ of mixture going in to cylinder.
(quality, quantity ).
3. When the choke valve is operated the flow of air into venturi ____________
(increases, decreases, remain constant)
4. The function of venturi shape in Carburettor is to decrease ____________
(velocity, pressure, temperature).
5. The breaking up and mixing the petrol with air is known as _____________
(Mixing, carburetion, scavenging).
6. Idling engine requires ____________ air fuel mixture. (lean, rich, no)
7. Carburettor is not used in ____________ engine (petrol, diesel, gas).
8. In a simple Carburettor as the speed of the engine increases the mixture will
become ____________. (rich, lean ).
EXPERIMENT NO. Date:
STUDY OF COOLING SYSTEMS OF I.C.ENGINE
After studying this practical, students are able to know.
(1) Need of cooling system.
(2) Applications of air cooling system & water cooling system.
(3) Construction, working, advantages & disadvantages of air cooling system.
(4) Construction working of mentioned water cooling system.
1. Direct or non-return system.
2. Thermosyphon system
3. Forced circulation system.
In internal combustion engines large amount of heat is produced during the
combustion of fuel in the engine cylinder. It is found that only 25-30% of the total heat
produced is converted into useful work. About 40% of the total heat is carried away
by the exhaust gases and the remaining about 30% of the total heat is absorbed by
the material of the cylinder and other components of the engine. The large amount
heat production is due to the fact that the temperature of the explosion is about 2000
to 2600 o
C. The temperature of the gases produced at the time of burning of the fuel
is above the melting point of aluminum which is 657o
C and that of iron which is
C. No metal can withstand such a high temperature continuously.
If this heat absorbed by the engine components is not dissipated by some
method of cooling, the temperature of the engine will soon reach a dangerous
temperature and will seriously harm the functioning of the engine. The piston will
seize in the cylinder due to expansion. Lubricating oil will break down, which may
result scoring of cylinders, the valves, will burn and wrap. Moreover the higher
temperature may also cause reduced. It is because of the fact that the mass of the
charge taken in during suction stroke is considerably reduced, due to its excessive
heating in the intake manifold. Consequently the power output is reduced. It is
therefore, very important that the unwanted heat which causes overheating of the
engine, should be dissipated by some methods of ~ooling.
ApplicaZions of air cooling: Air cooling is usually used for small engines and for
engines whose application gives extreme importance to weight such as aircraft
engines. Other areas for air-cooled engines are industrial and agricultural engines
wh~re there can be~a strong objection to use of water as coolant.
20or air cooling Zhe cylinder head transfer area is increased by finning and air is passed
over these fins to affect cooling.
Application of water-cooling: In case of water-cooled engines the cylinder and
the cylinder head are enclosed in a water jacket. This water jacket is connected to a
radiator (heat exchanger). Water is caused to flow in the jacket where it cools the
engine, then it gives up this heat to air 20n the radiator Znd is again circulated in the
TY21ES OF COOLING SÛSTEM:
In order to cool the engine a cooling medium is required. This can either be air
or liquid: Accordingly there are two types of systems in general use for cooling of
I.C.engines. They are-
• Air or Direcç cooling systemÃ
• Water or Indir<ct cooling systÛm.
AIR COOLING SYSTEM:
In this system, air is used as a cooling medium and it is used for small
capacity engines. Earlier it is used for big capacity air-craft engines as the water
cooling was not practically possible as the weight of water cooling system is very high
compared with air-cooling system.
The heat transfer coefficient for air-cooling is very low as mentioned earlier.
This heat transfer coefficient can be increased further by using the forced flow of air
over the engine surface. The heat transfer coefficient with air-cooling with forced
circulation is also considerably lower (50 W / m2
-K) compared with water cooling
system. The other method of increasing the heat transfer rate from the cylinder
surface is to increase the surface area by increasing the heat transfer rate from the
cylinder surface is to increase the surface area by providing the tins. The use of fins
increases the heat transfer surface by 5 to 10 times of its original value. In the air-
cooled systems, the forced circulation of air with increased surface area by using the
fins is commonly used in practice for aero-engines and motor cycle engines.
The sectional view of an engine-cylinder with fins is shown in Fig.( ). More fins
are used near the exhaust valve and cylinder heat where the possibility of occurrence
of maximum temperature exists.
The cooling fins are either cast integral with the cylinder and cylinder head or
they are fixed to the cylinder block separately. The number of the fins, used are 2 to
3 in case of cast fins and 4 to 5 in case of machined fins per centimeter. The height
of fin depends on the type of material and manufacturing process used. Generally the
height of fin used lies between 2 cm to 5cm and fin spacing is limited to 2.5 mm.
Advantages and Disadvantages of air-cooled system:
1. The design of air-cooled system is simple and less costly.
2. Each cylinder of the multi-cylinder engine can be removed separately as no
common cooling system is used for the engine. It is easy to renew in case of
3. There is no danger of leakage of the coolant.
4. The freezing in the cooling system is not at all a danger which is very common in
5. The installation of air-cooled system is easier as it does not require radiator,
headers and piping connections.
6. The weight of the cooling system per B.P. of the engine is far less than water
Air cooling results in higher engine temperature. This necessitates the
provision of bigger clearances between the various parts of the engine.
WATER COOLING SYSTEM:
In this system mainly water is used and made to circulate through the jackets
provided around the cylinder, cylinder-head, valve ports and seat sand other hot
spots where it extracts most of the heat. The diagrammatic sketch of water circulating
passage, viz, water jacket is shown in Fig.( ). It consists of a long flat, thin walled tube
with an opening, facing, the water pump outlet and a number of small opening along
its length that direct the water against the exhaust valves. The tubes, fits in the water
jacket and can be removed from the front end of the block. The heat is transferred
from the cylinder walls and other parts by convection and condition. The water
becomes heated in its passage through the jackets and is in turn cooled by means of
an air cooled radiator system. The heat from water in turn is transferred to air. Hence
it is called the indirect cooling system. Water cooling can be done by any one of the
following five methods.
Direct or non-return system
Forced circulation cooling system
Evaporative cooling system
Pressure cooling system
Direct or Non-Return System:
This system is useful for large installation where plenty of water is available.
The water from a storage tank is directly supplied through an inlet valve to the engine
cooling water jacket. The hot water is not cooled for reuse but simply discharged.
The arrangement of this system is shown in fig.( ). When the circulation of
water is achieved by virtue of its density difference, it is known as thermosyphon
Thermo-siphon circulation is based upon the fact that when water is heated up
its density decreases. Due to decrease in its density it tends to rise up. The cold
water take its place, as its density is relatively more. The rate of circulation is less as
the force causing the flow of water is limited.
The water as passed through the radiator is cooled by the flow of air passed
over the radiator tubes by the cooling fans. The cooled water rises to the cylinder
jacket, takes the heat from the cylinder wall and then it enters into the radiator from
the top header and comes down. It is cooled as it is passed through the radiator
The limitations of this system are listed below:
1. The engine should be placed as low as possible in relation to the radiator
as the force causing the flow is limited by the temperature difference of hot
and cold water.
2. The water level in the system should not fall below the level of the delivery
pipe, otherwise the circulation of water in the system will stop. This causes
the boiling of water and formation of steam resulting in further loss of water
which may damage the engine in a short period.
3. The use of this system is recommended for small capacity engines.
4. The main drawback of this system is that, the cooling depends only on the
temperature and is independent of engine speed. The rate of circulation is
Because of many limitations this system is rarely used presently.
The main advantage of this system is its simplicity and automatic circulation of
Forced Circulation Cooling System:
This system is used in large number of automobiles like cars, buses and even
heavy trucks. Here, flow of water from radiators to water jackets is by convection
assisted by pump. The main principle of the system is explained with the help of
block diagram shown in fig ( ). The water is circulated through jackets around the
parts of engine to be cooled, and is kept in motion by a centrifugal pump which is
driven from the engine. The water is passed through the radiator where it is cooled
by air drawn through the radiator by a fan and by the air flow developed by the
forward motion of the vehicle. A thermostat is used to control the water temperature
required for cooling. The system mainly consists of four component, viz., a radiator,
fan, water pump and a thermostat.
ADVANTAGES OF WATER COOLING SYSTEM:
1. Compact design of engines with appreciably smaller frontal area is possible.
2. The fuel consumption of high compression water cooled engines are rather lower
than for air cooled engines.
3. Because of even cooling of cylinder barrel and head due to jacketing makes it
possible to reduce the cylinder head and valve seat temperatures.
4. The size of engine does not involve serious problems as far as the design of
cooling system is concerned. In case of air cooled engines particularly in high
horse power range difficulty is encountered in the circulation of requisite quantity
of air for cooling purposes.
LIMITATIONS OF WATER COOLING SYSTEM:
This is dependent system in which supply of water for circulation in the jackets is
Power absorbed by the pump for water circulation is considerable and this affects the
power output of the engine.
Cost of the system is considerably high.
In the event of failure of the cooling system serious damage may be caused to the
Answer the following questions:
(1) Why cooling of engine is necessary? If we don't provide effective cooling system
than write down adverse effects to the engine?
(2) How heat transfer coefficient of air can be increased?
(3) Water cooling system is called indirect cooling system and air cooling system is
called direct cooling system?
(4) In thermosyphon system circulation of water takes place on the base of which
(5) Which is thermostat? Explain its function?
EXPERIMENT NO: DATE:
After studying this practical, students are able to know
(1) About common faults & remedies in IC engine.
AIM: Common Faults and Remedies in I.C.Engines.
Symptoms Causes Tests or Checks Remedies
(1) Engine fails
Lack of Ignition
(2) For battery Ignition –
(4) No fuel in the tank.
(5) No fuel in the
(6) Too much fuel in the
engine or flooded
(1) See if Ignition switch is on.
(2) Check the battery strength
by removing one of the spark
plug wire and holding it 10
mm away from the plug
when cranking the engine.
For no spark or weak spark
check the broken or loose
(3) Check spark plug gap.
(4) Check fuel level and the fuel
shut off cock.
(5) Check whether the fuel
pump supplies sufficient fuel,
after loosening fuel supply
line to carburettor ? If it
supplies sufficient fuel check
the carburettor. Check float,
float needle & starter device.
(6) Check whether the spark
plugs are wet or sooted.
(1) Switch on Ignition-c
(2) Recharge the batte
Join the broken or l
(3) Set the plug gap be
Tighten seat of all c
(4) Refuel or change ov
the fuel shut off coc
(5) Clean the fuel pump
air pump. Wash all
Clean the carburett
float, float needle &
insertion of gasket w
(6) Dry & clean the spa
throttle wide open.
(1) Air-fuel mixture very
(1) Check position of choke.
(2) Check fuel level in float
(3) Check exhaust pipe for
(4) Check valve tappet
(5) Check Ignition timing.
(1) Set it to proper clos
(2) Refill after cleaning
Set the float for pro
(3) Clean the exhaust p
(4) Set its right amount
(5) Advance the timing
(2) Air fuel mixture very
(1) Check Ignition timing. Check
carburettor for clogging.
(2) Check fuel supply lines &
(1) Clean the carburett
speed adjustment. S
(2) Repair the joints. If
intake pipe for leakage. pipeline.
(3) Spark plug fouled. (1) Check for soot or wetness.
Check the electrode gap.
(2) Contact breaker point
misadjusted, solied or pitted.
(3) Check if water in the fuel.
(1) Clean the spark plu
(2) Clean the contact p
the contact breaker
(3) Drain fuel & filter it.
(3) Engine is
(1) Defective starter
switch or lead.
(2) Battery discharged,
connections or lead
(3) Wrong grade of
engine oil in used or
frozen water pump
or defective starter.
(1) If lights are bright check the
(2) Check brilliance of head
(3) Test starter & compare
grade of oil according
specification of vehicle
(1) Replace starter swit
(2) Charge battery & re
(3) Use specified grade
replace the defectiv
(1) Inadequate petrol
(2) Defective pump.
(3) Ignition system
(4) Carburetion faults.
(1) Check petrol supply.
(2) Check operation of pump.
(3) Check Ignition system.
(4) Check carburettor for faults.
(1) Clean choked filter
(2) Correct pump faults
(3) Tight the connection
contact breaker stic
(4) Correctly set the mi
carburettor faults lik
piston, needle valve
(5) Engine has
(1) Rich Air : Fuel
(1) Check choke & See whether
the engine is flooded?
(1) Close the choke & O
while starting in case th
start in cold
(1) Cranking motor
speed very low.
(2) Storage battery
(3) Defective starting
(4) Petrol level in
carburettor very low.
(5) Weak or no spark at
the spark plug gap.
(1) Check temp. of motor oil.
(2) Check the battery for proper
(3) Check the motor.
(4) Check petrol level in the
carburettor after priming.
(5) Check spark at plug points.
(1) Heat it if it is very co
(2) Replace battery or W
while starting depre
(3) Start the engine by
(4) Repair the petrol su
filter & air vent hole
(5) Clean & remove ca
the plug point.
(1) Insufficient fuel
supply to the
(2) Fuel supply line
broken or closed.
(3) Fuel pump filter
(4) Fuel pump leaking.
(5) Sticking valve or
broken valve spring.
(1) Check the fuel supply pipe.
(2) Check fuel supply line for
(3) Check it.
(4) Check fuel pump leakage.
(5) Check the valve.
(1) Clean the fuel supp
(2) Clean fuel supply lin
line by means of ins
(3) Clean the filter or re
(4) Seal it with new gas
(5) Clean the valve and
Repair or replace if
(1) Very rich Air Fuel
(2) Sticking float and
not closing properly.
(3) Main jet very large
or wrongly adjusted.
(4) Wet air filter.
(1) Check the choke and throttle
(2) Check the adjustment of float
(3) Check the main jet.
(4) Check air filter.
(1) Close the choke an
(2) Replace the float ne
(3) Make standard adju
replace it, if require
(4) Clean and dry air fil
(1) Seized piston due to
(2) Failure of Ignition.
(3) Interrupted fuel
(1) Check oil level.
(2) Check the Ignition system.
(3) Check fuel supply line &
(1) (a) Allow it to cool.
(b) Top up with oil,
(c) Start with care.
(2) Set the Ignition syst
(3) Clean the fuel supp
(1) Check Ignition system,
contact breaker points & the
(1) Replace defective p
adjust breaker poin
(1) Worn out gudgeon
pin & small end
(2) Piston slaps due to
cylinder & ring wear,
(3) Big end bearing
(1) Short circuit each spark plug
(2) Noise will disappear when
each plug is short circuited in
(3) Short circuit plug in each
(1) Replace the worn o
(2) Replace the piston
(3) Repair big end bear
(1) Ignition fails to
(2) Choke opening.
(3) Fuel supply line
(4) Insufficient fuel
supplied by the fuel
(1) Check the Ignition system
(2) Check choke valve.
(3) Check the fuel supply line.
(4) Check the fuel pump.
(1) Replace the defecti
and do necessary s
Close the choke & ope
Clean & repair.
Repair the pump.
(5) Loose air intake
(6) Insufficient throttle
(7) Leaky pistons &
(8) Wrong Ignition
(9) Brakes blocking or
(5) Check manifold for air
(6) Check throttle linkage.
(7) Check for the leakage.
(8) Check for Ignition timing.
(9) Check brake mechanism &
locate the trouble.
Tighten the bolts and m
with new gasket, if requ
Adjust throttle opening.
Repair or replace pisto
Adjust the Ignition timin
Repair brake mechanis
clearance & adjustmen
(1) Defective Ignition
(1) Check Ignition lock. (1) Loose the cable of t
required, short circu
(1) Cylinder or ring
wear, broken or
(2) Burnt valve and
(3) Sticking valves.
(1) Check for blue smoke from
(2) Remove air filter and listen
for hiss from carburettor on
(3) Check gasket for leakage.
(1) Provide proper seal
(2) Replace the burnt v
(3) Provide proper tapp
(1) Insufficient water in
(2) Radiator furred or
(3) Fan belt slipping.
(4) Oil very low.
(1) Check water level in the
cooling water system.
(2) Check cooling system.
(3) Check fan and fan belt.
(4) Check oil level.
(1) Fill with water, if lev
(2) Clean radiator.
(3) Tighten fan belt.
(4) Top up the oil level,
EXPERIMENT NO. Date:
STUDY OF INTERNAL COMBUSTION ENGINES.
After studying this practical students are able to know
(1) About heat engine
(2) Advantages of IC Engine over EC Engine
(3) Classification of IC Engine.
(4) Basic nomenclature of IC engine
(5) Various components of IC engine & its functions
(6) Application of IC engine.
In general, an engine is defined as a device which converts one form of energy into
mechanical work. Heat engine is a device which transforms heat energy into
mechanical energy. Transformation of one form of energy into another required form
is always associated with losses. Therefore efficiency of conversion plays an
In every heat engine, some form of fuel (solid, liquid, gas or nuclear) is used. The
chemical energy of fuel is converted into thermal or heat energy & that is further used
to perform useful work.
Heat engines are mainly classified as
• External Combustion Engines. (E.C.engine)
• Internal Combustion Engines. (I.C.engine)
In E.C. engine working fluid is not mixed with fuel, therefore, the same working fluid is
used again & again. Steam engine / Steam turbine falls under this category.
• In I.C. engine, fuel is mixed with the air & burned, the combustion of fuel takes
place inside the engine cylinder and power is produced. This type of engines are
used in trucks & buses, scooters & cars, ships & locomotives, agricaltural & earth
moving machinery, many industrial applications & for power generation.
ADVANTAGES OF I.C.ENGINE:
Internal combustion engines have some special advantages over external
1. The thermal efficiengy of I.C.engine ( 35-40% ) is much higher than E.C.engine
2. Greater mechanical simplicity
3. Power developed by the I.C.engine per Kg weight of engine is higher, therefore it
is lighter & occupies less space.
4. The I.C.engine can be started quickly whereas an E.C.engine (Steam engine)
requires much more time as the steam has to be generated in the boiler.
5. The I.C.engine being more compact, practically it has no competitor for small &
portable power range.
6. The temperature in I.C.engine are very high (about 2000 C) as the combustion
takes place inside the engine cylinder, therefore, a cooling arrangement is
necessary to prevent overheating of engine cylinder.
7. In case of steam engines, fresh steam is circulated in the jackets to prevent
condensation & power loss.
8. I.C.engines are commonly single acting whereas steam engines are commonly
CLASSIFICATION OF I.C.ENGINE
The I.C.engines are classified as follows:
1. According to type of fuel used.
On this basis, I.C.engines are classified as petrol engine, diesel engine and gas
2. According to number of strokes required to complete the cycle.
On this basis they are classified as two stroke and four strokes engines.
In four stroke engines, the cycle is completed in four strokes of piston or two
revolutions of crank. And there will be one power stroke in two revolution of crank
In two stroke engines, the cycle is completed in two strokes of piston or one
revolution of crank shaft. And there will be one power stroke in each revolution of
3. According to methods of ignition:
They are classified as S.I.( Spark Ignition) engines and C.I.( Combustion Ignition)
S.I.engines: The compressed mixture of petrol and air ( i.e. charge) is ignited with
the help of introducing an electric spark with the help of spark plug, used in petrol
engines. (pressure: 70 bar)
C.I.engines: The fuel is ignited as it comes in contact with high temperature and
high pressure air (600 C & 3500 bar) i.e. compressed air in the cylinder. Diesel
engines works on this system.
4. According to cycle of operation:
They are mainly classified as Otto cycle engines and Diesel cycle engines.
Otto cycle : Combustion of fuel takes place at constant volume. Petrol engine
works on this cycle.
Diesel cycle: Combustion of fuel takes place at constant pressure. Diesel
engine works on this cycle.
5. According to method of cooling:
They are classified as air cooled or water cooled engines.
Air cooled engines: These engines are cooled with the help of passing air flow
over the surface of engines. Generally applicable for small capacity engines.
Water cooled engines: These engines are cooled by circulating cooling water
through the engine jackets. Generally used for high capacity engines.
6. According to method of governing used:
They are classified as quantity governing & quality governing:
Quantity governing: In this method the quantity of charge (mixture of petrol &
air) supplied to engine cylinder is controlled by throttle valve as per the
requirement. Petrol engines are governed by this method.
Quality governing: In this method the quantity of diesel injected into the cylinder
is controlled by control rack provided in fuel pump as per the requirement. Air fuel
ratio will very continuously.
7. According to speed of engine:
They are classified as low speed, medium speed and high speed engines.
Petrol engines are high speed engines whereas diesel engines fall under low or
medium speed engines.
8. According to arrangement of cylinder.
They are classified as horizontal, vertical, incline, V-type & radial engines.
Incline engine: All cylinders are arranged linearly and transmit power to a single
crank shaft. This type is very popular with automobiles, where 4 & 6 cylinder in
line engines are commonly used.
V-Type: In this arrangement, two cylinders are inclined at an angle (30-75) to
each other & with one crank shaft.
Radial engines: In this arrangement the cylinders are arranged along the
periphery of a circle. Previously this type engine was used in air craft engine.
Opposed piston engine: In this arrangement a single cylinder is used with
pistons moving in opposite direction. Therefore it is known as opposed piston
engines. The combustion takes place at the center for both pistons and no
cylinder head is required. Better balanced.
Opposed cylinder engine: In this arrangement, an engine with two cylinder
banks is located in same plane on opposite sides of the crankshaft.
BASIC ENGINE NOMENCLATURE:
1. Bore: Inside diameter of cylinder is known as bore
2. Stroke: The maximum linear distance travelled by the piston in cylinder in one
direction is known as stroke and it is equal to twice the crank radius.
3. Top dead centre (TDC): The extreme position of the piston at the top of the
cylinder (head end side) is clalled Top dead center position. In case of horizontal
engines this is known as Inner dead center (IDC) position.
4. Bottom dead centre: The extreme position of piston at the bottom of cylinder is
called Bottom dead center (BDC) position. In case of horizontal engine this is
known as (ODC) Outer dead centre position. The distance between these two
extreme positions is known as stroke length.
5. Clearance Volume : The volume contained in cylinder above top of piston when
the piston is at TDC is called the clearance volume. It is denoted by Vc.
6. Piston displacement or swept volume: The volume swept through by the
piston in moving between TDC & BDC is defined as piston displacement or swept
volume and it is denoted by Vs.
Vs = ×D×L Where, L =Length of stroke in m
N =Speed of the engine in RPM.
The cylinder volume = Swept volume(Vs) + Clearance volume(Vc).
7. Compression Ratio: The ratio of volume when the piston is at BDC to volume
when piston is at TDC is called compression ratio & It is denoted by
r = V1/V2 = (Vs+Vc) / Vc.
It is the ratio of volume, of working fluid, before compression to volume of working
fluid after compression.
For petrol engine the compression ratio varies from 5:1 to 9:1.
For diesel engine the compression ratio varies from 12:1 to 22:1
8. Piston speed: The distance travelled by the piston in one minute is known as
Piston speed = 2LN m/min
Where, L =Length of stroke in m
N =Speed of the engine in rpm.
VARIOUS COMPONENTS OF I.C.ENGINE:
Depending upon the design & application, one I.C.engine may be different
from the other I.C.engine, as regards its size, shape & dimensions. But the main
essential components becomes necessary to understand the purpose of various
components for complete understanding of I.C.engine. So now we shall discuss the
purpose of main components of I.C.engines.
• Frame: It generally consists of base plate, crankcase, and it also supports
different moving parts. The base plates are rigidly fixed to the foundation of the
floor. The lower part of crankcase contains oil for lubrication purpose.
• Cylinder and Cylinder Block: Single cylinder engine has a single cylinder. Multi
cylinder engine has a cylinder block which contains cylinder bores and openings
for the valves. To avoid wear and tear of cylinder block, cylinder liners are
provided. It may contain passage for flow of cooling water. The cylinder of
I.C.engine is considered as main body of the engine in which piston reciprocates
to develop power. It has to withstand very high pressure and temperature (about
2200 C) because there is direct combustion inside the cylinder therefore its
material should be such that it can retain strength at high temperature, should be
good conductor of heat and should resist to rapid wear and tear due to
reciprocating parts. Generally ordinary cast iron is used, but in case of heavy duty
engines, alloy steels are used. Sometimes, when engine blocks are heavy & for
easy maintenance sleeves or liners are inserted into cylinder which can be
replaced when worn out Liners are generally made of nickel chrome iron.
• Cylinder head: The cylinder head closes one end of cylinder. It houses inlet and
exhaust valves through which charge is taken inside the cylinder and burned
gases are exhausted to atmosphere from the cylinder. Cylinder head is usually
cast as one piece and bolted to the top of the cylinder. A copper and asbestos
gaskets are provided between the cylinder & cylinder head to obtain a gas tight
joint. The material used for cylinder head is also cast iron.
• Piston & Piston Rings: The functions of piston are to compress the charge
during compression stroke and to transmit the gas force to the connecting rod and
then to the crank during power stroke. The piston of I.C.engines is made of cast
iron, cast steel and aluminum alloy. The aluminum alloy has the advantage of
higher thermal conductivity and lower specific gravity. Piston is the heart of the
The piston rings are housed in the circumferential grooves provided on the outer
surface of the piston. It gives gas tight fitting between piston and the prevents the
leakage of high pressure gases. These are made of special grade cast iron. This
material retains its elastic property at very high temperature. The upper piston
rings are called the compression rings and the lower piston rings are called the
oiling or oil control ring ( oil scrapper rings).
• Connecting rod: It is usually a steel forging of circular, rectangular, I, T or H
section and is highly polished for increased endurance strength. Its small end
forms a hinge and pin joint with piston and its big end is connected to crank by
crank pin. It has a passage for the transfer of lubricating oil from the big end
bearing to small end bearing (gudgeon pin).
• Crank & Crank shaft: Both crank and crank shafts are steel forged and
machined to a smooth finish. These are held together by means of a key. Crank
shaft is supported in main bearings and has a heavy wheels called flywheel, to
even out the fluctuation of torque. The power required for any useful purpose is
taken from crank shaft only. The crank shaft is the back bone of the engine.
• Cam shaft: The function of the cam shaft is to operate the intake and exhaust
valves through the cams, cam followers, push rods and rocker arms. The cam
shaft is driven positively from the crankshaft at half speed of the crankshaft.
• Piston pin or wrist pin: Piston pin connects the piston and small end of
connecting rod. It provides the bearing for the oscillating small end of connecting
Inlet valve: It controls the admission of charge into the petrol engine or air into diesel
engine during suction stroke of the engine.
• Exhaust valve: The removal of exhaust gases after doing work on the piston is
controlled by this valve.
• Valve spring: Valves are kept closed by the valve spring (compression spring).
• Inlet manifold: It is the passage which carries the charge from carburettor to the
petrol engine. It connects all the inlet valves in case of multi-cylinder engine.
• Exhaust manifold: It is the passage which carries the exhaust gases from the
exhaust valve to the atmosphere.
• Cam shaft: The function of cam shaft is to actuate/operate the intake and
exhaust valves through the cams, cam followers, push rods and rocker arms. It is
driven positively from crank shaft at half the speed of the crank shaft.
• Cam & Cam follower: It gives the desired motion to the valves through the
• Push rod and Rocker arm: The motion of cam is transmitted to the valve
through push rod and rocker arm. These links together are also known as valve
• Crank case: It is the base which holds the cylinder and crank shaft. It also serves
as sump for lubricating oil.
• Water jacket: The jackets are the integral opening/passage provided around the
cylinder & other hot spots through which water is passed for cooling the engine.
• Flywheel: It is a wheel mounted on the crank shaft which stores excess energy
during power stroke and returns that energy during other strokes and maintains a
fairly constant output torque on the crankshaft.
• Governor: It is run by a drive from the crankshaft. The function of governor is to
regulate charge in case of petrol engine and amount of fuel in case of diesel
engine to maintain the speed of the engine constant, when the load requirement
• Carburettor: The function of carburetor is to supply the uniform air fuel to the
cylinder of a petrol engine through the intake manifold. The mass of mixture
entering the cylinder is controlled by a throttle valve.
• Spark plug: To ignite the compressed charge in petrol engine.
• Fuel pump: It forces fuel oil at high pressure through fuel nozzle into the cylinder
at the end of compression stroke in diesel engine.
• Fuel nozzle: The function of fuel nozzle is to break up the oil into a fine spray as
it enters the cylinder of diesel engine.
Applications of I.C.engines:
1 Road Vehicles
2.Scooters and Motor cycles
2 Locomotives 400-4000 CI 2,4 w
3 Small Air crafts
4 Marine Applications
5 Industrial Applications
2.Gas Pipe lines
6 Off-Road Vehicles
Answer the following questions.
(1) Define heat engine? How energy is liberated?
(2) Compare EC Engine & IC Engine?
(3) Define compression ratio. Write range of compression ratio for Diesel Engine &
Petrol Engine? Why compression ratio of Diesel Engine is more than
compression ratio of Petrol engine?
(4) Write down function & material of following components?
1. Frame 2. Cylinder block 3. Cylinder head 4. Piston 5. Piston rings 6.
Connecting rod 7. Crank & Crankshaft.
(5) Write function of following ?
1. Camshaft 2. Piston pin 3. Cam & follower 4. Push rod & rocker arm 5. Crank
case 6. Flywheel 7. Governor.
EXPERIMENT NO: Date:
STUDY OF THE IGNITION SYSTME OF PETROL ENGINE
After studying this practical, students are able to know
(1) Requirements of ignition system.
(2) Construction & working of battery ignition system.
(3) Construction & working of magneto ignition system
(4) Firing order of IC Engine.
(5) Construction & working of spark plug.
The petrol engines are spark ignition engines and in S.I.engines, the compressed (air
and petrol vapour mixture) charge must be ignited at the correct instant so that resulting rise
in pressure of hot gases acts on the piston when the piston is near top dead centre. The
expanding gases force the piston out in power stroke. A high voltage is required to jump the
gap of spark plug and give a spark of sufficient energy to ignite the mixture & this is
produced by ignition system.
REQUIREMENT OF IGNITION SYSTEM:
The important requirements of the spark ignition systems are listed below:
1. The voltage across the spark plug electrodes should be sufficiently large to produce an arc
required to initiate the combustion. The voltage necessary to overcome the resistance of
the spark gap and to release enough energy to initiate the self-propagating flame front in
the combustible mixture is about 10,000 to 20,000 volts.
2. The intensity of spark should lie in a specified limit because too high intensity may burn
the electrodes and too low intensity may not ignite the mixture properly.
3. The volume of the mixture (clearance volume) at the end of compression should not be
too large, otherwise the spark produced may not be sufficient to ignite the whole charge.
There is definite relation between the size of the spark and clearance volume.
4. There should be no missing cycle due to failure of spark.
5. In a multi-cylinder engine, there must be arrangement (distributor) to carry this voltage to
the right cylinder at the right time.
Now we will study the Battery ignition system & magneto ignition system used in petrol
BATTERY OR COIL IGNITION SYSTEM:
This system is used in cars and other vehicles using petrol engines. Fig(a)
Shows the circuit diagram of a battery or coil ignition system. The main components
of this system are: (a) a battery of 6 to 12 volts,(b) ignition switch, (c) induction coil,
(d) circuit or contact breaker, (e) condenser, (f) distributor, and (g) spark plugs.
There are two circuits in this system- One is primary circuit and the other is the
secondary circuit. The primary circuit consists of a battery, ignition switch, ammeter,
primary winding in the induction coil, contact breaker and a condenser. The
secondary circuit consists of secondary winding which has large number of turns of
fine wire in the induction coil, distributor, rotor and spark plugs. The primary winding
and secondary winding are wound on a laminated soft iron core and are insulated
from each other. One end of the secondary winding is earthed and other end is
connected to the distributor cap. The contact breaker is driven by a cam which
rotates at half the engine speed (for four stroke engines). There is a condenser in the
primary circuit. The condenser prevents the sparking at the contact breaker points.
Working of the battery or Coil ignition system:
When the ignition switch is switched on and the contact breaker point touches
a current flows the battery through the switch to the primary winding of the coil to the
circuit breaker points and the circuit is completed through the ground. The current
which flows through the primary winding of the coil produces a magnetic field in the
coil. When the primary circuit is opened by the contact breaker points, the magnetic
field collapses. Electromotive force is induced in the secondary winding of the coil. A
condenser is connected across the contact breaker in the primary circuit which helps
to collapse the field very quickly and produces a very high voltage in the secondary
coil as there are more turns of fine wire than in the primary coil. The voltage is
increased up to 20,000 volts. One end of the secondary coil is connected to the
ground and the other end is connected to the external terminal of the distributor. The
distributor connects the secondary coil to the different spark plugs. The distributor
directs this high voltage to the proper spark plug where it jumps the air gap of the
spark plug electrodes and the charge in that cylinder is ignited.
In a single cylinder engine the distributor is not required as in the case of motor
cycle engine, scooter engine and a single cam is sufficient for giving the spark.
MAGNETO IGNITION SYSTEM:
Magneto ignition system is generally used in small spark ignition engines,
such as in motor cycle and scooters. Fig.(b) Shows the circuit diagram of a magneto
This system consists of a magneto instead of battery, which produces and
supplies current in the primary winding. The magneto consists of a fixed armature
having primary and secondary windings and a rotating magnetic assembly which is
driven by the engine. It also consists of contact breaker, condenser, distributor rotor,
distributor and spark plugs. As the magnet turns, a magnetic field is produced from a
positive from a positive maximum to a negative maximum and back again. As this
valve falls from a positive maximum valve, as alternating current is induced in the
primary winding. This current flows in the primary circuit till the contact points are
closed. When the contacts open, a very high voltage is induced in the secondary
winding. This high voltage is then directed to the proper spark plug by the distributor.
The order in which the firing takes place in the different cylinders of a multi-
cylinder engine is known as the firing order. Proper firing order maintains proper
engine balancing and reduces engine vibration. Firing orders for various engines are
No. of Cylinders Firing order
Spark plug is used in S.I. engines (Petrol engines) to produce electric spark to
ignite the compressed air fuel mixture inside the engine cylinder.
The spark plug consists of three main parts:
1. A central electrode.
2. A threaded metallic body with a ground electrode.
3. An insulator separating the two electrodes.
The central electrode in the spark plug is surrounded by a porcelain insulator. The
central electrode extends for a short length through the bottom of the insulator. The
upper end of the central electrode is connected to the cable from the ignition coil. A
metal screw surrounds the bottom part of the insulator. The lower portion of the
screw is attached to a short electrode and bent towards the central electrode so that
there is a gap between the two electrodes. The air gap is kept between 0.6 mm to 1
mm. The high-tension current is given to the terminal of central electrode. This
current jumps the air gap between the central electrode and ground electrode. The
electrode metals are, Nickel, alloy of Nickel and Manganese, platinum alloy, alloy of
Nickel, manganese and silicon. Too large or too small air gap reduces the efficiency
of the entire ignition system.
State the functions of following components of Battery Ignition System:
2. Induction coil
3. Circuit or contact breaker
6. Spark Plug
1. ____________ is required to produce an are in S.I.engine (Injector, Spark plug,
2. Spark gap in spark plug is about __________. (0.7 mm, 1.6 mm, 0.7 mm).
3. Pre ignition means __________
4. In ignition system a spark is produced when contact breaker points _____.
5. The voltage induced in secondary coil depends on __________________.
(Thickness of wire, Conductivity of wire, Number of turns of coil)
6. The voltage required to produce spark is about __________. (2300, 2400, 10,000
7. Firing order of four cylinder petrol engine is ___________.(1-2-3-4, 1-2-4-3, 4-2-
EXPERIMENT NO: DATE:
STUDY OF LUBRICATING SYSTEMS OF I.C.ENGINES
After studying this practical students are able to know
(1) Need of lubricaating system
(2) Functions of lubrication system
(3) Properties of lubricating system
(4) Working of mentioned lubricating system
1. Splash lubricating system
2. Pressure feed lubrication system
3. Wet sump lubrication system
4. Dry sump lubrication system
Theory: The process of inserting a film of oil in between the moving parts so as to
reduce friction is known as lubrication. Any metallic surface, regardless how highly it
has been finished or polished, shows crests or depressions when it is seen with the
help of microscope. These crests and depressions on one surface interlock with
crests and depressions on the other mating surface. When one surface slides over
the other, friction is developed. The friction produces heat which results wear and
tear of sliding or rotating surfaces. Moreover, a large amount of power produced by
engine is wasted to overcome the force of friction.
Almost all machine parts of an I.C.engine have relative motion and rub against each other.
The lubrication is required to reduce this rubbing action and increases the life of engine.
The purpose of lubrication in I.C.engine are reducing the rubbing action between different
machine parts having relative motion with each other and removing the heat generated
inside the engine cylinder.
The power developed inside the engine is known as Indicated Power (I.P.), but the power
available at the crankshaft (Brake Power) is always less than I.P. This is because, part of
the power is lost in bearings, cylinder and piston, gears and many other parts due to
friction. It can be reduced by using lubrication between the parts which have relative
motion with each other, as film of lubricant does not allow metal contact.
The frictional resistance between two mating parts having relative motion is
mostly dependent on lubricating oil properties, surface condition, material of
surfaces, rate of relative motion, nature of relative motion and quantity of lubricating
FUNCTIONS OF LUBRICATION:
1. To reduce friction between the mating parts, so as to keep the moving parts
sliding freely over each other, and increases the power output.
2. To reduce wear and tear of the moving parts.
3. To reduce noise and to increase engine life.
4. To act as a cooling medium for removing heat from the bearings, cylinders &
5. To form a good seal between piston rings and cylinder walls, thus avoiding the
loss of power which is caused due to leakage of pressure.
6. To absorb and carry away harmful substances resulting from incomplete
7. To act as a cleaning agent, cleaning the bearing and piston rings from dust,
carbon & micro metal chips and thus it keeps the parts clean.
8. To prevent metallic components from corrosive attack due to acid formation
during combustion process.
PROPERTIES OF THE LUBRICATION OIL:
For proper functioning of reciprocating and rotating parts of the engine, the
lubricating oil must possess certain properties. Some of the important properties are
1. Viscosity: Viscosity of an oil is a measure of its resistance to flow and is usually
measured in terms of Saybolt Universal Seconds (SUS), which is the time
required, in seconds, for a given quantity of oil to flow through a capillary tube
under specified test conditions. Viscosity is measured at two temperatures –18o
F) and 99o
F). It is also expressed in centi-stokes, centi-poise and
Redwood seconds, depending upon the type of viscometer used for its
2. Viscosity Index: The viscosity of oil is affected by its temperature. Higher the
temperature lower is the viscosity. This variation of viscosity of oil with changes in
a temperature is measured by term Viscosity Index (VI). A high viscosity index
number indicates relatively smaller changes in viscosity of the oil with
temperature. The oil is compared with two reference oils having same viscosity at
C. One is paraffinic base oil (considerable change in viscosity with
temperature) is arbitrarily assigned an index of zero (0) and the other is a
nepthenic base oil (little change in viscosity with temperature) assigned an index
As a thumbrule, oil having VI below 50 are considering to be low viscosity
index oil, oils having VI between 50 to 80 are considered medium viscosity index
oil & oils having VI more than 80 are considered high VI oils.
TYPES OF LUBRICATION SYSTEMS:
(1) Splash Lubrication System
(2) Pressure Feed Lubrication System
(3) Mist/Charge Lubrication System
(4) Wet Sump Lubrication System
(5) Dry Sump Lubrication System
(1) Splash Lubrication System:
The arrangement of the system is shown in Fig.( ). This method generally used
for vertical engines with a closed crankcase. The sump is located at the bottom of the
crankcase. When the engine crankshaft rotates, the big end of the connecting rod
splashes oil by centrifugal action. The connecting rod big eng has a hollow pipe
called a scoop which is fitted to the bearing gap and pointed towards the direction of
the rotation of the crank shaft. The lubricating oil passing through the scoop, lubricate
the big end bearing and gudgeon pin bearing. All other parts are lubricated by the
splash. Excess oil is collected in the troughs located as shown in figure and are
provided with overflows and collected in the main sump. The level of the oil in trough
is maintained constant. The dripping from the cylinders is also collected in the sump.
The oil from the sump is recirculated with the help of the pump as shown in figure.
The inability to regulate the quantity of oil splashed against the cylinder wall or
inability to keep the oil from getting past the piston head into the combustion
chamber, burning with the fuel and passing out with exhaust gases are the limitations
of this system.
(1) Pressure Feed Lubricating system:
All modern car and bus engines are lubricated by high pressure feed system as
shown in Fig.(B). Such a system supplies oil under pressure ( 2 to 5 bar) directly to
the connecting rod bearings, to the camshaft bearings, to the valve gear and to the
camshaft drive. Indirect supplies reach the cylinder walls, the gudgeon pin, the
distributor and pump drives.
Oil is carried in the sump, a deep tray which closes the bottom of the crankcase
and is circulated by the by the gear pump which sucks from the sump through a
strainer as shown in figure. The pump delivery pressure is controlled by a relief valve
and the oil passes through a very fine filter before it reaches the main distributor
gallery. From the various bearings, surfaces and gears, the oil simply drains into the
After lubricating the big end bearings, the oil is fed to the gudgeon pins through
the oil-way in the connecting rod and further squirted into the cylinder wall.
(2) Mist OR Charge Lubrication System:
This is the simplest method of lubrication and does not require oil-further and oil
pump. In this system the lubricating oil is per-mixed with the petrol therefore the fuel
carries the lubricating oil in the cylinder which helps for lubricating the petrol therefore
the fuel caries the lubricating oil in the cylinder which helps for lubricating the piston
and cylinder. Most of the oil burns with the fuel due to high temperature and burnt oil
is carried with the exhaust gases. The lubricating oil cannot be recovered in this
This type of lubrication is generally used for two stroke spark ignition engines of
scooter and motorcycle. The quantity of lubricating oil mixed with the petrol is 3 to 6
% of petrol.
The advantages of this system are listed below:
(1) It does not require separate lubricating system so it is most economical.
2 (2) There is no risk of failure of lubrication system.
(3) The lubricating oil supplied is regulated at various loads and speeds by
the increased fuel flow.
The carbon deposits due to the burning of the oil on the spark plug and on other
parts and non-recovery of the oil used are the main disadvantages of this system.
The lubricating systems are also classified as wet-sump lubrication and dry
sump lubrication system.
(3) Wet sump Lubricating System:
The arrangement is shown in Fig.( ). This is called wet sump as sump is always
full of oil. The working is just similar to the pressure feed lubricating system.
Oil is drawn from the sump by an oil pump through an oil strainer. A pressure
relief valve is provided which automatically maintains the delivery pressure constant.
If the pressure exceeds than the predetermined pressure, the valve opens and allows
some of the oil to return to the sump and relives the oil pressure in the system. The
oil from the pump goes to the bearings and part of it passes through a filter which
removes solid particles from the oil. As all the oil is not passed through the filter, the
system is known as by-pass filtering system. Advantage of this system is that a
clogged filter will not restrict the flow of oil to the engine.
(4) Dry sump Lubricating System:
The dry sump lubricating system is shown in Fig.( ). This is known as dry-sump
as the sump does not contain oil and all the oil required for lubrication remains in the
circulation only. High-speed racing cars and military jeeps use this type of lubricating
system as the oil in the wet sump is subjected to large back and forth acceleration.
An auxiliary tank is used to supply the oil to the main bearings with the help of
the pump. The oil returns back to tray and then returned back to auxiliary tank by
scavenging pump, the capacity of which is always 20 to 30% more than the pressure
pump to avoid flooding of the crank-case.
If the filter is clogged, the pressure relief valve opens permitting oil to flow
bypassing the filter and reaches the supply tank. The oil is then circulated to the
bearing form the supply tank. A separate oil cooler is used to cool the oil to remove
the heat form the oil, as heating of oil is rapid because of rapid circulation of oil and
high speed of the engine.
(1) Define lubrication? Write adverse effects if lubricating system is not proper?
(2) Frictional resistance depends up on which factors?
(3) Define viscosity index? Write unit of viscosity?
(4) Why splash lubricating system is named splash?
(5) Write benefits & draw back of mist lubricating system?
(6) What is the main difference between wet sump lubricating system & dry sump
EXPERIMENT NO. DATE:
PREPARATION OF HEAT BALANCE SHEET OF I.C.ENGINE
After studying this practical, students are able to know
(1) Measurements necessary to draw heat balance sheet.
(2) Take necessary readings for following measurement
• Brake power
• Rate of fuel consumption
• Heat carried away by cylinder jacket cooling water
• Heat carried away by exhaust gases
(3) Prepare observation table
(4) Do calculation of
• Brake power
• Heat supplied by combustion of fuel
• Heat carried away by exhaust gases
• Heat carried away by cooling water
• Unaccounted heat
(5) Prepare heat balance sheet
(6) Conclude the practical.
They are carried out for the purpose of comparing actual results with the theoretical
or ideal performance. For such tests it is necessary to measure losses in addition to
the useful part of the energy and also to draw up a heat balance account.
The measurements necessary to draw up the heat balance account are
1. Brake power
2. Rate of fuel consumption
3. Heat carried away by exhaust gases
4. Heat carried away by cooling water
BRAKE POWER MEASUREMENT:
Brake power can be obtained by the use of either machanical, electrical,
hydraulic or pneumatic dynamometer etc. Here mechanical brake is used to measure
the brake power.
A rope brake dynamometer consists of one or more ropes (in our case one
rope) wrapped around the fly wheel of an engine whose power is to be measured.
The upper end of the rope is attached to a spring balance and the downward end is
kept in place by a dead weight. The rotation of flywheel produces frictional force and
the rope tightens. Consequently a force is induced in the spring balance. Generation
of heat is enormous and that necessitates a cooling arrangement for the brake. The
rim is made through and kept in place by the centrifugal force.
Let W be the dead weight. S be the spring balance reading. D be the brake
drum diameter and d be the rope diameter. Then effective radius of the brake drum
would be Reff = (D+d)/2 and braking torque would be (S- W) Reff
Brake Power = 2πN (S- W) Reff = 2πN(S-W)(D + d/2)
MEASUREMENT OF RATE OF FUEL CONSUMPTION:
Burette is used to measure the mass of fuel consumed. During normal
working, fuel is supplied from the tank. To measure the mass of fuel consumed three
way cock is turned in such a way that fuel is supplied from burette and supply of fuel
from tank is stopped. Measure the time required to consume certain amount of fuel.
Now turn the three-way cock such that fuel is supplied from tank.
MEASUREMENT OF HEAT CARRIED BY CYLINDER JACKET COOLING WATER:
In ordinary I.C.engines, the circulation of cylinder jacket cooling water is
maintained by means of natural gravitation current of water or by force circulation
from a pump. (First one is used here). To measure the rate of flow of jacket cooling
water, water meter can be fitted in the inlet pipe or one can collect the outflow water
in a measuring vessel in a given interval. It is also necessary to measure the inlet
and outlet temperature of water.
Let Mw = mass of cylinder jacket cooling water supplied in Kg/min
T1 = Inlet temp. of jacket cooling water K.
T2 = Outlet temp. of jacket cooling water K.
Cp = Specific heat of water kJ/Kg K
MEASUREMENT OF HEAT CARRIED AWAY BY THE EXHAUST GASES:
The actual determination of heat carried away by exhaust gases is concerned
with three quantities, namely, the temp. of exhaust gases and room temperature, the
mass of exhaust gases, and the mean specific heat of exhaust gases.
Temperature of exhaust gases: The temperature of exhaust gases (tg) as they
leaves the engine cylinder can be measured by a thermocouple or thermometer. The
thermocouple or thermometer is encased in a tube which is screwed into the exhaust
connection of the cylinder.
Mass of exhaust gases: It may be calculated from the measured air
consumption by air-box orifice method or by air flow meter in a given time.
Mass of exhaust gases per minute = Air consumption per minute
+ Fuel consumption per minute
= (1 + Air Fuel ratio) mf
HEAT BALANCE SHEET:
In order to complete the heat balance sheet for an I.C.engine, it should be
tested over a period of the time under condition of constant load and speed. All
measurements listed earlier should be taken at regular interval of time. At the
completion of the trial the necessary data should be averaged out and a heat account
should be drawn up as follows:
In kJ % Heat Expenditure In kJ %
(1) Heat equivalent to
(2) Heat carried away
by cooling water
(3) Heat carried away
by exhaust gases
(4) Observation error
and radiation losses.
1. Dead weight W = _________N.
2. Spring balance reading S = __________N
3. Engine speed N = ________rpm
4. Pulley diameter D = 300 mm
5. Rope diameter d = 12.7 mm
6. Reff. = _______mm
7. Time required to consume ______ml of fuel = ______sec.
8. Rate of fuel consumption mf = _________kg/sec
9. Calorific value of fuel C.V. = 44,000 kJ/kg
10.Mass of jacket cooling water supplied mw = _________Kg/sec
11.Inlet temperature of cooling water T1 = ________K
12.Outlet temperature of cooling water T2 = _________K
13.Temperature of exhaust gas T3 = _________K
14.Ambient temperature T4 = _______K
15.Air fuel ratio = 20
16.Mass of exhaust gas mg = (1 + air fuel ratio) mf = ________kj/sec
17.Specific heat of exhaust gas Cpg = 2.1 kJ/kg-K
18. ρp = 0.86 gm/cm3
19.Cpw = 4.2 kJ/kgK
20. ρw = 1000 kg/m3
(1) Brake power:
Brake power = 2πN |S- W| Reff
Heat Equivalent to brake power = __________Kj
(2) Heat supplied by combustion of fuel:
Heat supplied = mf × C.V.
(3) Heat carried away by exhaust gases:
Heat carried away by exhaust gases = mg Cpg (T3 – T4)
(4) Heat carried away by cooling water:
Heat carried away by cooling water = mw Cpw (T2 –T1)
to pass 10 ml
2 liter fla
EXPERIMENT NO. DATE:
THE VALVE TIMING DIAGRAM OF A 4-STROKE AUTOMOBILE ENGINE
After Studying this practical students are able to know.
(1) Ideal valve timing diagram.
(2) Factor which affects ideal valve timing diagram.
(3) Actual valve timing diagram.
APPARATUS: 4-Stroke I.C.engine, marking pencil, feeler gauge, a device for
measuring crank angles.
In 4-stroke SI engine the opening and closing of the valves, and the ignition of
air-fuel mixture do not take place exactly at the dead centre positions. The valves
open slightly earlier and close after their respective dead centre positions. The
ignition also occurs prior, to the mixture is fully compressed, and the piston, reaches
the dead centre position. A typical valve-timing diagram of a SI engine is shown in
Similarly, in a CI engine both valve do not open and close exactly at dead
centre positions, rather operate some degrees on either side in terms of crank angles
from the dead centre positions. The injection of the fuel (diesel) is also timed to occur
earlier. A typical valve timing diagram of a diesel engine is shown in fig.
There are two factors, on mechanical and other dynamic, for the actual valve
to be different from theoretical valve timing.
(A) Mechanical factor: The poppet valve of the reciprocating engines are opened
and closed by cam mechanisms. The clearance between cam, tappet and valve
must be slowly taken up and valve slowly lifted, at first, if the noise and wear to be
avoided. For the same reason valve cannot be closed abruptly, else it will bounce
on its seat. Thus the valve opening and closing periods are spreaded over a
considerable number of crank shaft degrees. As a result, the opening of the valve
must commence ahead of the time at which it is fully opened (before dead
centre). The same reason applies for the closing time and the valve must be
closed after the dead centers.
(B) Dynamic factor: Besides the mechanical factor of opening and closing of valves,
the actual timing is set taking into consideration the dynamic effect of the gas
INTAKE VALVE TIMING:
Intake Valve timing has bearing on actual quantity of air sucked during the
suction stroke i.e. it affects the volumetric efficiency. For both low and high speed
engine the intake valve opens 10o
before the arrival of the piston at TDC on the
exhaust stroke. This is to insure that the valve will be fully open and fresh charge
starting to flow into the cylinder as soon as possible after TDC. As the piston moves
out in the suction stroke, the fresh charge is drawn in through the intake valve. When
the piston reaches charge tends to cause it to continue to move into the cylinder. To
take advantage of this, the intake is closed after TDC so that maximum air is taken
in. This called ram effect. However, if the intake valve is to remain open for too long a
time beyond BDC, the up moving piston on the compression stroke would tend to
force some of the charge, already in the cylinder, back into the intake manifold. The
time the intake valve should remain open after TDC is decided by the speed of the
engine. At low engine speed the charge speed is low and so the air inertia is low, and
hence the intake valve should be close relatively early after BDC. In high-speed
engines, the charge speed is high, and consequently the inertia is high and hence to
induct maximum quantity of the charge due to ram effect the intake valve should be
close relatively late after BDC (up to 60o
after BDC). There is limit to the high speed
engine for advantage of ram effect. At very high speed the effect of the fluid friction
may be more than offset the advantage of ram effect and the charge for cylinder per
cycle falls off.
EXHAUST VALVE TIMING:
The exhaust valve is set to open before BDC (say about 25o
before BDC in
low speed engines and 55o
before BDC in high speed engines). If the exhaust valve
did not start to open until BDC. The pressure in the cylinder would be considerably
above the atmospheric pressure during the first portion of the exhaust stroke,
increasing the work required to expel the exhaust gases. But opening of the exhaust
valve earlier reduces the pressure near end of the power stroke and thus causes
some loss of useful work on this stroke. How ever the overall effect of opening the
valve prior to the time the position reaches BDC results in overall gain in output.
The closing time of the exhaust valve effects the volumetric efficiency. By
closing the exhaust valve few degrees after TDC (about 15o
in case of the low speed
engine and 20o
in case of the high speed engines) the inertia of the gases tends to
scavenge the cylinder by carrying out a greater mass of the gas left in the clearance
volume. This results in increased volumetric efficiency.
There may be period when both inlet and exhaust valve are open at the same
time. This is called valve over-lap (15o
in case of low speed engine and 30o
in case of
high-speed engine). This overlap should not be excessive otherwise it will allow the
burned gases to be sucked into the intake manifold, or the fresh charge to escape
through the exhaust valve.
1. Fix a plate on the body of the engine touching the flywheel.
2. Mark the positions of both dead center on the flywheel with reference to the fixed
plate TDC and BDC in case of vertical engines, and IDC and ODC in case of
3. Mark on the flywheel when the inlet and exhaust valves open and close as the
flywheel is rotated slowly.
4. Measure periphery of flywheel.
5. Measure distances of valve opening closing from BDC or TDC.
6. After calculations plot actual valve timing diagram.
Periphery = _______cm.
Sr. No. Valve timings
Distance from TDC
or BDC in cm
Angles from TDC of
BDC in degree
1. Marking plaZe should be fixZd properly withBthe flywheel.
2. T54e positions of he dead centers™and locations oç opening and clÿsing of
valves hould be marked™carefully.
Answer the following questions:
(1) What do you mean by valve timing diagram?
(2) What is mechanical factors?
(3) Why inlet vafve is opened before TDC & closed after BDC?
(4) Why exhaust valve ~s opened before™BDC & closed after TDC?
(5) Why ignition takes plaÛe before TDC?
(6) Zhat is valve ovZrlap? Write useBulness of valve overlap. What are adverse
effecZs if we keep vaZve overlap more<than required?