Internal Combustion Engine There are two main types of heat engines: internal combustion engines and external combustion engines. In an internal combustion engine, fuel combustion occurs inside the engine cylinder and the hot gases directly power the piston. This includes gasoline/petrol engines. The four strokes of a petrol engine are: intake, compression, power, and exhaust. In the intake stroke, air/fuel mixture enters the cylinder. In the compression stroke, the mixture is compressed. In the power stroke, combustion powers the piston. In the exhaust stroke, spent gases are pushed out.

1. Internal Combustion Engine

2. Introduction :
 =
 Heat engine : It can be defined as any engine that
converts thermal energy to mechanical work output.
Examples of heat engines include: steam engine, diesel
engine, and gasoline (petrol) engine.
 On the basis of how thermal energy is being delivered to
working fluid of the heat engine (or as to where the
combustion of fuel takes place), heat engine can be
classified as an internal combustion engine and external
combustion engine.
Thermal
energy
Mechanical
work

3. Internal Combustion Engine
 In an Internal combustion engine, the combustion of fuel
produces heat energy inside the engine cylinder. The products of
combustion directly act upon the piston and develop power, which is
used to rotate the crank shaft.
 Petrol engine is an example of internal combustion
engine, where the working fluid is a mixture of air and
fuel.
 IC Engines are used as main prime movers in
commercial vehicles.

4.  External combustion
engines are those in which
combustion takes place
outside the engine cylinder.
External Combustion Engine
For example: In steam engine or steam turbine, the heat
generated due to combustion of fuel is employed to generate
high pressure steam,which is used as working fluid in a
reciprocating engine or turbine.

5. I.C. ENGINE
 Combustion is inside engine
cylinder.
 Working fluid: petrol, diesel and
other gases.
 Requires less space.
 Capital cost is low.
 Starting of engine is easy and
quick.
Combustion is outside engine
cylinder.
Working fluid: steam
Requires large space.
Capital cost is high.
Starting of engine takes more time
and isn't easy.
E.C. ENGINE

6. I.C. ENGINE
 Thermal efficiency is high.
 Power developed per unit weight
of these engines is high.
 Fuel cost is relatively higher.
 Used for small capacity power.
 Wide application for road
vehicles, locomotives, machine
practices, aircrafts etc.
Thermal efficiency is low,
Power developed per unit weight of
these engines is low.
Fuel cost is relatively lower.
Not convinient and economical for
small power range.
Limited applications - Railway
locomotives, power generation etc.
E.C. ENGINE

7. Engine Classification
Even though basic parts are the
same, design differences can
change the way engines operate
and how they are repaired
For this reason, you must be able
to classify engines

8.  According to type of fuel used.
Petrol engine.
Diesel engine.
Gas engine.
Bi-fuel engine.
 According to number of strokes per cycle.
4 – stroke engines.
2 – stroke engines.
 According to method of cooling
Air cooled engine.
Water cooled engine.
Engine Classification

9. Engine Classification
 According to method of ignition.
Spark ignition.
Compression ignition.
 According to the cycle of combustion.
Otto cycle.
Diesel cycle.
Duel combustion.
 According to the number of cylinders.
Single cylinder.
Multi cylinder.

10. Acc. to cylinder arrangement
(Refers to the position of the cylinders in relation to the crankshaft)
• Inline Engines: The cylinders
are arranged in a line, in a
single bank.
• V Engines: The cylinders
are arranged in two banks,
set at an angle to one
another.
• Opposed cylinder Engines:
The cylinders are arranged
in two banks on opposite
sides of the engine

11. Acc. to cylinder arrangement
• Radial Engines: The cylinders
are arranged radially, in a
circle.
• Opposed piston Engines: The
pistons are arranged in two
different cylinders on
opposite sides of the engine

12. Engine Details

13.  Cylinder : Heart of the engine, where
fuel is burnt and power is developed. It
has to withstand high pressure and
temperature, because combustion of
fuel is carried out within the cylinder.
Therefore, cylinder at times is covered
via cooling towers. The piston
reciprocates indise the cylinder.
 Cylinder Head : covers the top of
cylinder and provides space for valve
mechanism, sparks plug, fuel injector
etc.
Engine Details
Cylinder Head

14.  Piston : It's a close fitting hollow cylinderical
plunger reciprocating inside the cylinder.
Power developed via combustion of fuel is
transmitted by piston to the crank shaft
through connecting rods.
 Piston Rings : Metalic rings inserted into
circumferential grooves provided at the top of
piston. These help in maintaining a gas-tight
joint between piston and cylinder.
 Piston Pin or Gudgeon pin : It's the pin
joining small end of connecting rod and
piston. It's made of steel.
Engine Details

15.  Connecting Rod : Member connecting
piston (through piston pin) and crank shaft
(through crank pin). It converts the
reciprocating motion of the piston into rotary
motion of the crankshaft.
 Crank and crank shaft : Crank is a lever
that is connected to big end of connecting
rod and other end is rigidly connected to a
shaft, called crankshaft. Crank rotates about
the axis of crankshaft and causes the
connecting rod to oscilliate.
 Valves: These are devices which control the
flow of intake and exhaust gases.
Engine Details

16. Connecting rod
Connecting Rod
Cam Shaft
Connecting Rod
Valves

17.  Flywheel : It's a heavy wheel,
mounted on the crankshaft of the
engine and minimizes cyclic
variation in speed.
 Crank case : It's the lower part of
the engine, serving as an enclosure
to crankshaft and also as a sump
for lubricating oils.
Engine Details
Flywheel
Flywheel

18.  Carburetor : It's used in
petrol engine for proper
mixing of air and fuel.
 Fuel Pump : It's used in
diesel engine for increasing
pressure and controlling of
fuel supplied to the injector.
 Fuel Injector : It's used to
inject diesel fuel in the form
of fine atomised spray under
pressure.
 Spark Plug : It's used in
petrol engine to produce a
high intensity spark for
ignition of air and fuel
mixture in the cylinder.
Engine Details
Spark Plug

19. I.C. ENGINE TERMINOLOGY
 Bore (D) : The inner
diameter of the engine
cylinder is termed as bore.
 Stroke (L) : It's the linear
distance travelled by piston,
as it moves from one end of
the cylinder to the other end.
It's equal to twice the radius
of crank.
crankrL *2=

20. I.C. ENGINE TERMINOLOGY
 Dead Centres : In vertical
engines, the top most
position of the piston is
termed as Top Dead Centre
(TDC) and bottom most
position of piston is Bottom
Dead Centre (BDC).
IDC ODC
In horizontal engine, the extreme
position of the piston, close to the
cylinder head is called Inner Dead
Centre (IDC) and extreme position of
piston near crank is called Outer
Dead Centre (ODC).

21. I.C. ENGINE TERMINOLOGY
 Clearance Volume (Vc) : It's
the volume contained
between top and cylinder
head, when the piston is at
TDC or IDC.
 Swept Volume (Stroke
Volume, Vs) : It's the volume
displaced by the piston in
one stroke.
LDVS **4/ 2
∏=
Compression Ratio (r) : The ratio of
total cylinder volume (Vc + Vs) to the
clearance volume (Vc).
)()( CCS VVVr ÷+=

22. I.C. ENGINE TERMINOLOGY
60)2( ÷= LNVP
 Piston speed (VP) : It's the
average speed of piston.
The unit of Piston Speed
(VP) is m/s,
whereby,
L = Stroke Length
N = Speed of Crank shaft
(RPM)

23. OTTO FOUR STROKE CYCLE
(FOUR STROKE PETROL ENGINE or SPARK
IGNITION FOUR STROKE ENGINE)
A Four Stroke Internal Combustion Engine is an engine whose
working cycle consists of an intake (or suction) stroke, a compression
stroke, a power stroke and an exhaust stroke.

24.  Inlet valve opens and the exhaust valve is closed.
 Presure in the cylinder will be atmospheric.
 As piston moves from TDC to BDC, volume in the cylinder
increases and simultaneously the pressure decreases.
 This creates a pressure difference b/w atmosphere and inside of
the cylinder. Due to this pressure difference, petrol and air mixture
enters the cylinder through carburetor.
 This stroke is represented by horizontal line 1-2 on the P-V
diagram.
 The crankshaft has now made a half rotation, i.e., 180° of crank
angle.
 At the end, the cylinder will be completely filled with petrol and air
mixture, called charge, and the inlet vavle is closed.
Suction or Intake stroke:

25.  Both the inlet valve and the exhaust valve are closed.
 As piston moves from BDC to TDC, the petrol and air mixture
contained in the cylinder will be compressed.
 Thus pressure and temperature of the mixture increases.
 The process of compression is shown is shown by 2-3 on the p-v
diagram.
 Near the end of the stroke, petrol and air mixture is ignited by
electric spark, which is given out by spark plug.
 Combustion of fuel releases hot gases, which will increase the
pressure at constant volume.
 This constant volume combustion process is represented by vertical
line 3-4 on the p-v diagram.
Compression stroke:

26.  Both the inlet valve and the exhaust valve are closed.
 As piston moves from TDC to BDC, the high pressure and high
temperature burnt gases force the piston to perform the stroke,
called Power Stroke (Expansion or working stroke).
 The engine produces mechanical work or power, during this stroke.
 As the piston moves from TDC to BDC, the pressure of the hot
gases gradually decreases and volume increases (curve 4-5 on p-v
diagram).
 Near the end of stoke the exhaust valve opens, which releases the
burnt gases to atmosphere.
 This drop of pressure at constt. volume is represented by vertical
line 5-6 on the p-v diagram.
Power (expansion) stroke:

27.  During this stroke the exhaust valve opens and the inlet valve is
closed.
 The piston moves from BDC to TDC.
 During this stroke, the piston pushes the exhaust gases
(combustion product) out of the cylinder at constant pressure.
 This stroke is represented by horizontal line 2-1 on the P-V
diagram.
Exhaust stroke: