1. Cylinder 9. spark plug 2. Cylinder head 10. inlet valve 3.
Piston 11. exhaust valve 4. Connecting rod 12. cooling fins 5.
Crank and crankshaft 13. carburretor 6. Crank pin and bearings 14.
flywheel 7. Piston rings 15. main bearings 8. Gudgeon pin 16. valve
mechanism
Slide 3
:The internal combustion engines are classified based on the
following systems 1) based on number of strokes per cycle : (a)four
stroke engine in which one cycle is completed in four strokes of
the piston in two revolutions of the crankshaft. (b)two stroke
engine in which one cycle is completed in two strokes of the piston
in one revolutions of the crankshaft.
Slide 4
2) Based on thermodynamic cycle used : (a) Constant volume
combustion cycle or Otto cycle. (b) Constant pressure combustion
cycle or diesel cycle. (c) Partly at constant volume and partly at
constant pressure combustion cycle or dual combustion cycle. 3)
Based on number of cylinders : (a) Single cylinder engine. (b)
Multicylinder engine.
Slide 5
4) Based on arrangement of cylinder : (a) In line engines : in
this all the cylinder are arranged with their axes parallel and
transmit the power to a single crank-shaft. (b) V-engines : these
engines contain two banks of cylinder connected to same crank and
crank-shaft. Their axes are inclined to each other. (c) Radial
engines : in this the cylinders are arranged radially and are
connected to a single crank-shaft. (d) Opposed cylinder engine :in
this engine there are two cylinder banks which are located in the
same plane on opposite sides of crankshaft. (e) Opposed piston
engine : in this engine cylinder houses two pistones, each of which
drives a separate requires no cylinder head.
Slide 6
5) Based on ignition system : (a) Spark ignition (s.i) engines:
petrol engines use the spark ignition system for igniting the
compressed charge. (b) Compression ignition (c.i) engines : diesel
engines utilize the high temperatures raised due to high
compression ratio of the cylinder. 6) Based on cooling system : (a)
Water cooled engines. (b) Air cooled engines. 7) Based on fuel used
: (a) Petrol engines. (b) Diesel engines. (c) Gas engines (d)
Bi-fuel engines : these engines use the main fuel as gas and the
liquid fuel is used for the starting purposes.
Slide 7
8) Based on fuel supply system : (a) Carburettor engines : in
such engines the mixture of petrol and air from carburettor is
supplied to the engine cylinder. (b) Solid injection engines : in
case of diesel engines the fuel is injected with the help of a fuel
pump. (c) Air injection engines : in certain diesel engines the
fuel is injected into the cylinder with the help of compressed air.
9)Based on lubrication system : (a) wet sump lubrication (b) Dry
sump lubrication (c) Pressure lubrication
Slide 8
Sr. no. Descriptions.i. enginec.i. engine 1.Basic cycleBased on
Otto cycleBased on diesel cycle 2.Fuel usedGasoline (petrol) having
high self ignition temperature. Diesel having lower self ignition
temperature compared to gasoline. 3.InductionA carburettor is used
to prepare the required strength of mixture of fuel and air. No
carburettor is needed. Fuel is injected with the help of fuel pump
under high pressure directly into the combustion chamber before the
end of compression stroke. 4.Compressio n ratio (C.R.) Various from
5 to 9. upper limit is limited by antiknock rating of fuels.
Various from 14 to 20. upper limit is fixed due to increasing
weight of the engine with the increase in C.R.
Slide 9
Sr. No.Descriptions.i. enginesc.i. engines 5.ignitionSpark is
need to ignite the mixture. The self ignition of fuel occurs due to
high temperature of air because of high compression of air. 6.Load
controlQuantity of mixture of fuel and air inducted is controlled
by throttle. Fuel pump regulates the supply Of fuel injected to
cylinder. 7.Speed.High speed engines due to light weight. Low speed
engines due to heavy weight. 8.Thermal efficiency Low efficiency
due to low compression ratio (C.R.) High efficiency because of
higher compression ratio (C.R.) 9.weightLighter due to lower peak
pressures. Heavier due to higher peak pressures. 10.startingEasy
due to low C.R.Difficult due to high C.R. 11.Running costMore as
they use costly fuel.Low as they use cheap fuel. 12.Initial
cost.Lowhigh
Slide 10
In two stroke engines, one cycle is completed in one
revaluation of the crankshaft by eliminating the suction and
exhaust strokes. However, the suction and exhaust processes are
carried out simultaneously during the compression and expansion
strokes. The working of s.i. and c.i engines working on two stroke
cycle are being describe below.
Slide 11
Fig. shows the schematic diagram of two stroke engine. In this
type of engine the valves of the four stroke engine art replaced by
ports which are three in numbers, namely transfer port, inlet or
induction port and exhaust port.
Slide 12
Consider that the piston is at T.D.S. which has the high
pressure and high temperature gases of the previous stroke and the
fresh charge in the crank case. When the piston moves from T.D.S.
to B.D.C., the burnt gases expand and develop the motive power.
After completion of about 80% of expansion stroke, the piston
uncovers the exhaust port and some of the products of combustion
escape to atmosphere. During the upward motion of the piston from
B.D.C. to T.D.C., the piston fist uncovers the inlet port allowing
the fresh charge to be admitted into the crank case due to the
partial vacuum created and then it uncovers the transfer and
exhaust ports. The fresh charge admitted into cylinder in its
previous stroke is now compressed. Before the end of compression
stroke a spark is supplied which burns the fuel air mixture. Cycle
is again repeated.
Slide 13
Fig shows the schematic diagram of a two stroke diesel engine.
The fuel is supplied with the help of fuel injection pump and the
injector to the cylinder. The working of diesel engine is similar
to two stroke S.I. engine except that only air is inducted into the
crank case of C.I. engine in place of mixture of fuel and air.
Slide 14
Consider the piston at T.D.C. when piston moves down, the hot
gases expand. During its downward motion, the piston firstly
uncovers the exhaust port and a little later it uncovers the
transfer port. The air compressed during the previous stroke in the
crank case is transferred into the cylinder via the transfer port.
This incoming air pushes out the burnt gases while passing over the
deflector. This process of sweeping out the burnt gases is called
scavenging. The piston moves upwards i.e. from B.D.C. to T.D.C. it
first closes the transfer port and a little later the exhaust port.
Before the end of compression stroke, the fuel is injected and the
atomized fuel burns due to high temperature of air called auto
ignition. The resulted hot gases will again expand, thus completing
a cycle.
Slide 15
o Piston moves from TDC to BDC o creating vacuum in the
cylinder o Intake valve opens allowing only o air to enter the
cylinder and o exhaust valve remains closed
Slide 16
o Both valves stay closed o Piston moves from BDC to TDC, o
compressing air to 22:1 o Compressing the air to this extent o
increases the temperature inside the o cylinder to above 1000
degree F
Slide 17
o Both valves stay closed. o When the piston is at the end of
compression stroke(TDC) the injector sprays a mist of diesel fuel
into the cylinder. o Expanding gases push the piston from TDC to
BDC
Slide 18
o Piston moves from BDC to TDC o Exhaust valve opens and the
exhaust gases escape o Intake valve remains closed
Slide 19
The working of a diesel engine is similar to petrol engines
working on Otto cycle except that in case of C.I. engines the air
is only drawn during its suction stroke instead of mixture of fuel
and air drawn in case of S.I. engines In case of C.I. engines the
fuel is injected into the cylinder before the end of compression
stroke under very high pressures. The compression ratio used for
diesel engines various from 14 to 24.
Slide 20
sr.no.AspectFour stroke cycle engine Two stroke cycle engine
1.Completion of cycleCycle is completed in four strokes of the
piston or in two revaluations of the crankshaft. Cycle is completed
in two strokes of the piston or one revaluation of the crankshaft.
2.Power produced for same cylinder dimensions and speed. lessHigh
power produced is almost twice of four stroke engine, practically
70% to 80% higher. 3.Size of flywheelHeavier flywheel is needed
since turning moment is not so uniform. Lighter flywheel is needed
since more uniform turning moment is produced.
Slide 21
Sr. no. AspectFour stroke diesel engineTwo stroke diesel engine
4.Initial cost and space requirement for same size of engine.
Occupies more space. And costly due to complicated valve mechanism
Cheaper and occupies less space. 5.Thermal efficiency highLow since
some fresh charge escapes during scavenging process. 6.Volumetric
efficiency High due to more time available for induction. Low due
to less time available for induction. 7.startingComplicated
arrangement needed. easy 8.noiselessmore 9.Cooling and lubrication
Lesser cooling and lubrication is needed since it has only one
power stroke per revolution of crankshaft. Normally water cooled.
More cooling and lubrication is needed since it has one power
stroke per revolution of crankshaft. Normally air cooled.
10.ApplicationCars, trucks,, generators, etc.Scooters, motor cycles
etc.