The document provides an introduction to internal combustion engines. It discusses the basic differences between internal and external combustion engines and classifications of internal combustion engines based on fuel, cycle of operation, and combustion process. It then describes the basic parts and working principles of 4-stroke petrol and diesel engines as well as 2-stroke petrol engines. Key differences between petrol and diesel engines are also highlighted. The document concludes by defining common terminology used in internal combustion engines.

1. UNIT- I
INTRODUCTION
TO
IC ENGINES

2. HEAT

3. HEAT AND WORK

4. CONVERTIONS
• WORK can be completely converted into
HEAT but HEAT cannot be completely
converted into WORK .
• THE DEVICE WHICH CONVERTS
HEAT INTO WORK IS ENGINE

5. Classifications:
Internal Combustion Engines (IC Engines)
External Combustion Engines (EC Engines)
Internal Combustion Engines (IC Engines):
IC Engines are those in which combustion of
fuels take places inside engine cylinder (Example:
Petrol, Diesel,GAS)
External Combustion Engines (EC Engines):
EC Engines are those in which combustion of
fuels take places outside engine cylinder (Example:
Steam Engine, Steam turbine)

6. Classification of IC Engines:
a. According to the cycle of operation
Spark ignition engines(Petrol or Constant volume
or Otto cycle)
Compression ignition engines(Diesel or Constant
Pressure)
b. According to the type of fuel used
Petrol, Diesel, Gas Engine.
c. According to the method of fuel
SI & CI
d. According to the Process of combustion
Otto cycle, Diesel cycle, Dual combustion cycle

7. Basic Parts of IC Engines:
cylinder,
cylinder head,
piston,
connecting rod,
crankshaft,
flywheel
Camshaft,
crankcase,
piston pin,
crankpin,
piston rings &oil ring

8. About Petrol Engine:
A petrol engine (also known as a gasoline engine in North America) is an
internal combustion engine with spark-ignition, designed to run on petrol (gasoline).

9. Working Cycles Four Stroke Petrol Engine:
 It is also known as Otto cycle or constant volume cycle.
 Cycle of operation is completed in 4-strokes of the piston or 2 revolutions of the
crankshaft.
 Each stroke consists of 180°, of crankshaft rotation and hence a cycle consists of 720°of
crankshaft rotation.
2-stroke: 1 power stroke per 1 crankshaft rev
4-stroke: 1 power stroke per 2 crankshaft rev
Principle of Operation:
The series of operations of an ideal four-stroke SI engine are as follows
Suction Stroke or charging stroke
Compression Stroke
Expansion or Power Stroke or working stroke
Exhaust Stroke

10. Principle of Operation

11. Principle of Operation:
Stroke Valve Position
Suction Stroke
Suction Valve open
Exhaust Valve closed
Compression Stroke Both Valves closed
Expansion or Power
Stroke
Both Valves closed
Exhaust Stroke
Exhaust Valve open
Suction Valve closed

12. Suction Compression Ign.-Combn. Expansion Exhaust

13. FOUR STROKE SI ENGINE

14. FOUR STROKE ENGINE

15. Working Principles of Four Stroke Diesel Engine:
Increased pressure of combustion gases acts on piston -> converted
to rotary motion
Can be 2 or 4 stroke engines
2-stroke: 1 power stroke per 1 crankshaft rev
4-stroke: 1 power stroke per 2 crankshaft rev
Engine stroke:
A stroke is a single traverse of the cylinder by the piston (from
TDC to BDC)
1 revolution of crankshaft = 2 strokes of piston

16. Working Principles of Four-Stroke Diesel Engine
Strokes
Intake
Compression
Power
Exhaust

17. Working Principles Of Four Stroke Diesel Engine:
Intake stroke
Intake valve open, exhaust valve shut
Piston travels from TDC to BDC
Air drawn in
Compression stroke
Intake and exhaust valves shut
Piston travels from BDC to TDC
Temperature and pressure of air increase

18. Working Principles Of Four Stroke Diesel Engine:
Power stroke
Intake and exhaust valves shut
Fuel injected into cylinder and ignites
Piston forced from TDC to BDC
Exhaust stroke
Intake valve shut, exhaust valve open
Piston moves from BDC to TDC
Combustion gases expelled

19. FOUR STROKE CI ENGINE

20. Working Principles Of Two Stroke Petrol Engine

21. Working Principles Of Two Stroke Petrol Engine

22. Ignition types
Petrol Engine Diesel Engine
Spark Ignition Compression Ignition

23. 23
Two Stroke Cycle Petrol Engine -
Construction
Construction :
•A piston reciprocates inside the cylinder
•It is connected to the crankshaft by means of connecting rod and
crank
•There are no valves in two stroke engines, instead of valves ports
are cut on the cylinder walls.
•There are three ports, namely inlet, exhaust and transfer ports.
•The closing and opening of the ports are obtained by the movement of
piston. The crown of piston is made in to a shape to perform this.
•A spark plug is also provided.

24. 24
Two stroke cycle Petrol Engines - Working
First Stroke : (Compression, ignition and inductance)
(Upward stroke of piston)
(a) compression:
• The piston moves up from Bottom Dead Centre (BDC)
to Top Dead Centre (TDC)
• Both transfer and exhaust ports are covered by the
piston.
• Air fuel mixture which is transferred already into the
engine cylinder is compressed by moving piston.
• The pressure and temperature increases
• at the end of compression.

25. 25
Two stroke cycle Petrol Engines - Working
First Stroke : (Compression, ignition and
inductance) (Upward stroke of piston)
(b) Ignition and Inductance:
• Piston almost reaches the top dead centre
•The air fuel mixture inside the cylinder is ignited by means of
an electric spark produced by a spark plug
•At the same time, the inlet port is uncovered by the plane.
•Fresh air fuel mixture enters the crankcase through the inlet port

26. 26
Two stroke cycle Petrol Engines - Working
Second Stroke: (Downward Stroke of the engine) :
(c)Expansion and Crankcase compression
•The burning gases expand in the cylinder
•The burning gases force the piston to move down. Thus useful
work is obtained.
•When the piston moves down, the air fuel mixture in the
crankcase is partially compressed.
This compression is known as Crank case compression.

27. 27
Two stroke cycle Petrol Engines - Working
Second Stroke: (Downward Stroke of the engine) :
(d) Exhaust and transfer:
•At the end of expansion, exhaust port is uncovered.
•Burnt gases escape to the atmosphere.
•Transfer port is also opened. The partially compressed air fuel mixture
enters the cylinder through the transfer port.
•The crown of the piston is made of a deflected shape. So the fresh charge
entering the cylinder is deflected upwards in the cylinder.
•Thus the escape of fresh charge along with the exhaust
gases is reduced.

28. Compression
Intake and exhaust valves shut
Piston travels from BDC to TDC
Temperature and pressure of air increase
Power stroke
Intake and exhaust valves shut
Fuel injected into cylinder and ignites
Piston forced from TDC to BDC
Working Principles Of Two Stroke Diesel Engine

29. Working Principles Of Two Stroke Diesel Engine
• Strokes
– Compression
– Power
– (Intake/Exhaust)

30. Working Principles Of Two Stroke Diesel Engine

31. Application Of Four stroke Cycle Engine
Used in heavy vehicles
Buses,
Lorries,
Trucks etc.,
Application Of Two stroke Cycle Engine
Used in light vehicles
Bikes,
Scooters,
Mopeds
Ship propulsion

32. Application Of Four stroke Petrol Engine
Buses ,Trucks
Mobile electric generating sets.
Small pumping sets with side cars
Application Of Four stroke Diesel Engine
30kw-Tractors
40to 100kw – jeeps, buses and trucks
200 to 400kw-Earthmoving m/c
100 to 35000kw-Marine application

33. 33
I.C ENGINE TERMINOLGOGY

34. 34
I.C ENGINE TERMINOLGOGY
The standard terms used in I.C Engines are
1. Bore: Inside diameter of the cylinder is termed as Bore
and it is designated by the letter d and is usually expressed
in millimeter (mm)
2. Top Dead Center (TDC): The extreme position reached
by the piston at the top of the cylinder in the vertical
engine is called Top Dead center. It is also called the Inner
dead centre (IDC).
3. Bottom Dead Center (BDC): The extreme position
reached by the piston at the Bottom of the cylinder in the
vertical engine is called Bottom Dead center. It is also
called the Outer dead centre (ODC).

35. 35
I.C ENGINE TERMINOLGOGY
4. Stroke: The nominal distance travelled by the piston
in the cylinder between the extreme upper and lower
positions of the piston (TDC &BDC) is termed as
stroke and it is designated by the letter Land is usually
expressed in millimeter (mm)
5. Compression ratio (r): It is the ratio of Maximum
cylinder volume to the Clearance volume.
6. Cylinder volume (v): It is the sum of swept volume
and the Clearance volume.
V = Vs + Vc

36. 36
I.C ENGINE TERMINOLGOGY
• 7. Displacement (or)Swept volume (Vs): It is the
volume of space generated by the movement of
piston from one dead center to another dead center.
It is expressed in terms of cubic centimeter (cc) and
given by
VS = A * L = π * d2
* L / 4
8. Clearance Volume( Vc): It is the space in the
cylinder, when the piston is at Top Dead Center It is
designated as VC and expressed in cubic centimeter
(cc).

37. Comparison of Petrol and Diesel Engines
Petrol Engines
1. A petrol engine draws a
mixture of petrol and air
during suction stroke.
2. The carburettor is employed to
mix air and petrol in the
required proportion and to
supply it to the engine during
suction stroke.
3. Pressure at the end of
compression is about 10 bar.
4. The charge (i.e. petrol and air
mixture) is ignited with the
help of spark plug.
Diesel Engines
A diesel engine draws only air
during suction stroke.
The injector or atomiser is
employed to inject the fuel at the
end of combustion stroke.
Pressure at the end of
compression is about 35 bar.
The fuel is injected in the form of
fine spray. The temperature of
the compressed air is
sufficiently high to ignite the
fuel.

38. Comparison of Petrol and Diesel Engines
(contd..)
10. The maintenance cost is less.
11. The thermal efficiency is about
26%.
12. Overheating trouble is more
due to low thermal efficiency.
13. These are high speed engines.
14. The petrol engines are
generally employed in light
duty vehicle such as scooters,
motorcycles and cars. These
are also used in aeroplanes.
The maintenance cost is more.
The thermal efficiency is about
40%.
Overheating trouble is less due
to high thermal efficiency.
These are relatively low speed
engines.
The diesel engines are generally
employed in heavy duty vehicles
like buses, trucks, and earth
moving machines.

39. ENGINE SPECIFICATIONS

40. ENGINE SPECIFICATIONS

41. ENGINE SPECIFICATIONS

42. ENGINE SPECIFICATIONS

43. ENGINE SPECIFICATIONS

44. ENGINE SPECIFICATIONS

45. ENGINE SPECIFICATIONS

46. ENGINE SPECIFICATIONS
Engine capacity : 177.4cc
Engine type : single cylinder, air cooled 4st
Max Power : 17.3bhp @ 8500rpm
Max Torque : 1.58kgm @ 6500rpm
Gear box : 5 speed constant mesh
Fuel system : carbureted
Front brake : 270mm petal disc brake
Rear brake : 200mm petal disc brake
Front suspension : Telescopic hydraulic fork
Rear suspension : gas shocks
Front tyre: 90/90 x17
Rear tyre : 110/80 x 17
Height : 100mm
Length : 2085mm
Width : 730mm
Ground clearance : 180mm
Kerb weight : 137kg
Fuel tank capacity : 16 liters