INTERNAL COMBUSTION

ENGINES

P. Marimuthu, M.E
Teaching Fellow
CEG, Anna University
Heat engine:
• An engine is complex unit in which different components are assembled together,
and fuel is burned to produce power or energy.
• A heat engine is a device which transforms the chemical energy of a fuel into
thermal energy and uses this energy to produce mechanical work. It is classified
into two types-
(a) External combustion engine
(b) Internal combustion engine

2
External combustion engine:
• The fuel is burned externally and the produced steam is used for the mechanical
movement, it is called an External Combustion (EC) engine.
Examples:

• In the steam engine or a steam turbine plant, the heat of combustion is employed to
generate steam which is used in a piston engine (reciprocating type engine) or a
turbine (rotary type engine) for useful work.
• In a closed cycle gas turbine, the heat of combustion in an external furnace is
transferred to gas, usually air which the working fluid of the cycle.

3
Internal combustion engine:
• In this engine, the combustion of air and fuels takes place inside the cylinder and are
used as the direct motive force.
Examples:
Automobiles

4
External combustion engine Internal combustion engine

Combustion of air-fuel is outside the Combustion of air-fuel is inside the engine

engine cylinder (in a boiler) cylinder (in a boiler)

The engines are running smoothly and Very noisy operated engine
silently due to outside combustion

Higher ratio of weight and bulk to output It is light and compact due to lower ratio of
due to presence of auxiliary apparatus like weight and bulk to output.
boiler and condenser. Hence it is heavy and
cumbersome.

Working pressure and temperature inside Working pressure and temperature inside
the engine cylinder is low; hence ordinary the engine cylinder is very much high; hence
alloys are used for the manufacture of special alloys are used
engine cylinder and its parts.

5
External combustion engine Internal combustion engine

It can use cheaper fuels including solid High grade fuels are used with proper
fuels filtration

Lower efficiency about 15-20% Higher efficiency about 35-40%

Higher requirement of water for dissipation Lesser requirement of water

of energy through cooling system

6
7
Open cycle gas tubine 8
Wankel Engine 9
Petrol Engine 10
Diesel Engine 11
Steam Engine 12
Stirling Engine 13
Steam Turbine 14
Closed cycle gas turbine 15
Ic Engines can be classified into the following types:

1. According to the basic engine design-

(a) Reciprocating engine (Use of cylinder piston arrangement),

(b) Rotary engine (Use of turbine)

2. According to the type of fuel used-

(c) Petrol engine,

(b) diesel engine,

(c) gas engine (CNG, LPG),

(d) Alcohol engine (ethanol, methanol etc)

3. According to the number of strokes per cycle-

(a) Four stroke and

(b) Two stroke engine

16
4. According to the method of igniting the fuel-
(a) Spark ignition engine,
(b) compression ignition engine
5. According to the working cycle-
(c) Otto cycle (constant volume cycle) engine,
(b) Diesel cycle (constant pressure cycle) engine,
(c) dual combustion cycle (semi diesel cycle) engine.
6. According to the fuel supply and mixture preparation-
(a) Carburetted type (fuel supplied through the carburettor),
(b) Injection type (fuel injected into inlet ports or inlet manifold, fuel injected
into the cylinder just before ignition).
7. According to the number of cylinder-
(a) Single cylinder and
(b) multi-cylinder engine
8. Method of cooling-
(a) water cooled
(b) air cooled
9. Speed of the engine-
(a) Slow speed,
(b) medium speed and
(c) high speed engine
10. Cylinder arrangement-
(a) Vertical,
(b) horizontal,
(c) radial,
(d) V-type
11. Valve design and location-
(a) Overhead (I head),
(b) side valve (L head)
18
12. Port design and location-
(a) cross scavenging,
(b) loop scavenging,
(c) uniflow scavenging.
13. Method of governing-
(a) Hit and miss governed engines,
(b) quantitatively governed engines and
(c) qualitatively governed engine
14. Application-
(a) Automotive engines for land transport,
(b) marine engines for propulsion of ships,
(c) aircraft engines for aircraft propulsion,
(d) industrial engines,
(e) prime movers for electrical generators.

19
Single Cylinder Engine 20
Multi Cylinder Engine 21
Horizontal Engine 22
Vertical Engine 23
Radial Engine 24
5/13/2021 V Engine 25
Valve Position 26
 Main Components of Ic Engines

• Engine Block • Inlet Valve

• Cylinder head • Exhaust valve
• Cylinder block • Intake,Exhaust manifold
• Oil sump • Spark plug
• Cylinder
• Fuel Injector
• Cylinder Liners
• Carburetor
• Piston
• Cam shaft
• Piston Rings
• Flywheel
• Crank and Crank shaft
• Crank case

27
Parts of Ic Engine 28
Engine Parts 29
Engine Parts 30
31
Cylinder block 32
Cylinder head:
The top end of the cylinder is covered by cylinder head over which inlet and
exhaust valve, spark plug or injectors are mounted. A copper or asbestos gasket is
provided between the engine cylinder and cylinder head to make an air tight joint.
The cylinder head is also single-casted unit and bolted to the top portion of
the cylinder block. The combustion chamber is a part of the cylinder head, where
the combustion of gases takes place. The water passages are provided to remove
the heat from the cylinder head. In latest engines, the cylinder head also houses the
camshaft which has the inlet and exhaust valves with supportive valve mechanism.
Provision is made to fix spark plug in SI engines and nozzle in CI engines. The
lower portion of the cylinder head is well-machined to ensure there is no leakage
of gases.

33
Piston and Piston Rings:
Piston is a cylindrical unit, used to compress
the charge during compression stroke and to
transmit the gas force to the connecting rod
and then to the crankshaft during power
stroke.
Transmit the force exerted by the burning of
charge to the connecting rod. Usually made
of aluminium alloy which has good heat
conducting property and greater strength at
higher temperature and is light in weight.

34
Piston rings:
These are housed in the circumferential grooves provided on the outer surface
of the piston and made of steel alloys which retain elastic properties even at high
temperature. 2 types of rings- compression and oil rings. Compression ring is
upper ring of the piston which provides air tight seal to prevent leakage of the
burnt gases into the lower portion. Oil ring is lower ring which provides effective
seal to prevent leakage of the oil into the engine cylinder.
The piston rings are placed in the ring groove and provide sealing between
the piston and the cylinder liner, thereby preventing the leakage of high pressure
gases.

35
Connecting Rod:
The major function of the connecting rod is to
convert the reciprocating motion of piston to
the rotary motion of the crankshaft.
It is usually manufactured by using
drop-forged steel.
Its small end is connected to the piston with
the help of gudgeon pin and the big end is
connected to the crankpin with shell bearings.
It has a passage for the transfer of lubricating
oil from the big end bearing to the small end
bearing .

36
Crank and Crankshaft:

The crankshaft is called the backbone of an engine

because it converts the reciprocating motion of piston
into the rotary motion.

Front end of the crankshaft will transmit drive to the

camshaft and also to the timing gear, whereas the
flywheel is bolted to the flange at rear end of the
crankshaft.
The special steel alloys are used for the
manufacturing of the crankshaft. It consists of
eccentric portion called crank.

37
• Inlet Valve: The major role of the inlet valve is to submit fresh
charge in to the cylinder during the suction stroke.

• Exhaust Valve: The exhaust valve removes out the burnt gases
from the combustion chamber after power stroke.

• Valve Spring: The valve spring plays an important role to close

the valve and also provides air tight compartment to seal the
combustible gases during power stroke.

• Camshaft: The major function of the camshaft is to operate the

intake and exhaust valves through the cam lobe.

• Flywheel: It is a wheel mounted on the crankshaft which stores the

energy during the power stroke and transmits the energy to the
transmission system, the clutch and then to the gear box. 38
• Governor: It is run by drive from the crankshaft. The function of the governor is to

regulate the 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

varies

• Crank case: It houses cylinder and crankshaft of the IC engine and also serves as

sump for the lubricating oil.

• Carburettor: The major function of the carburetor is to supply carburized fuel as

per speed and the engine load.

• Spark Plug: The function of the spark plug is to ignite the fuel air mixture after

completion of the compression stroke in an engine.

• Fuel Injector: The function of fuel injector is to break the fuel into fine spray

(atomized condition) as it enters the combustion chamber of diesel engine

39
40
 Classification of Ignition Type
• On the basis of the process of ignition, the automobile engines are classified into

– spark ignition (SI) engine (petrol or gas)

• 4 stroke SI engine

• 2 stroke SI engine

– compression ignition (CI) engine (diesel)

• 4 stroke SI engine

• 2 stroke SI engine

• The spark ignition engine can be differentiated from the compression ignition engine as per the following

factors.

(i) The type of fuel used.

(ii) The way the fuel enters in the combustion chamber.

(iii) The way in which fuel is ignited.

41
 Spark Ignition Engine (Petrol Engine)
• The spark ignition engine uses a highly volatile fuel, such as
gasoline(Petrol), which turns into vapor easily.
• The fuel is mixed with air before it enters in the combustion chamber, and
forms a combustible air-fuel mixture.
• This mixture then enters the cylinder and gets compressed with the help of
a piston.
• An electric spark is produced by the ignition system which ignites the
combustible air-fuel mixture.
• The combustible gases burn and expand, which forces the piston
downwards for generating power.

42
Compression Ignition Engine (Diesel Engine)

• In the compression ignition engine or diesel engine, only fresh air enters
the cylinder, which is compressed to a very high pressure and temperature,
which could go up to 1000°F (538°C).
• The diesel is then injected or sprayed into the engine combustion chamber.
• This spray contains very fine and tiny particles of diesel in an atomized
form.

• The hot air or heat of compression ignites the fuel and generates the power
stroke.

43
Working of Four stroke SI engine:
The four-stroke engine is the most common types of internal combustion engine and
is used in various automobiles.
A four stroke engine delivers one power stroke for every two revoution of the
crankshaft/4 strokes of the piston.
(i) Suction stroke (suction valve open, exhaust valve closed)-charge consisting of fresh
air mixed with the fuel is drawn into the cylinder due to the vacuum pressure created by
the movement of the piston from TDC to BDC.
(ii) Compression stroke (both valves closed)-fresh charge is compressed into clearance
volume by the return stroke (BDC to TDC) of the piston and ignited by the spark for
combustion. Hence pressure and temperature is increased due to the combustion of fuel
(iii) Expansion stroke (both valves closed)-high pressure of the burnt gases force(TDC)
the piston towards BDC and hence power is obtained at the crankshaft.
(iv) Exhaust stroke (exhaust valve open, suction valve closed)- burned gases expel out
due to the movement of piston from BDC to TDC.
44
4-stroke S.I (petrol engine)

45
 Working of 4 Stroke SI Engine
Suction Stroke Compression Stroke Power Stroke Expansion Stroke

At the beginning
of stroke
Piston position / At TDC / At BDC / At TDC / At BDC /
Travel TDC to BDC BDC to TDC TDC to BDC BDC to TDC
IV, EV condition IVO / EVC IVC / EVC IVC / EVC IVC / EVO

Action inside Air, Fuel mixture is A/F mixture is Combustion of Burnt gases are
cylinder sucked inside the compressed & charge & pushed out through
cylinder through Spark is ignited mechanical power exhaust valve
inlet valve opening output opening

At the end of
stroke
Piston position At BDC At TDC At BDC At TDC

IV, EV condition IVC / EVC IVC / EVC IVC / EVO IVO / EVC

Crank shaft
rotation

46
47
Actual Valve Timing Diagram

48
P-V Indicator diagram

49
Working of Four stroke CI engine:
A four stroke CI engine delivers one power stroke for every two revoution of the
crankshaft / 4 strokes of the piston.
(i) Suction stroke (suction valve open, exhaust valve closed)-charge consisting of fresh
air is drawn into the cylinder due to the vacuum pressure created by the movement of the
piston from TDC to BDC.
(ii) Compression stroke (both valves closed)-fresh air is compressed into clearance
volume by the return stroke (BDC to TDC) of the piston and injected by the fuel for
combustion. Hence pressure and temperature is increased due to the combustion of fuel
(iii) Expansion stroke (both valves closed)-high pressure of the burnt gases force(TDC)
the piston towards BDC and hence power is obtained at the crankshaft.
(iv) Exhaust stroke (exhaust valve open, suction valve closed)- burned gases expel out
due to the movement of piston from BDC to TDC.

50
4-stroke C.I (Diesel engine)

51
 Working of 4 Stroke CI Engine
Suction Stroke Compression Stroke Power Stroke Expansion Stroke

At the beginning
of stroke
Piston position / At TDC / At BDC / At TDC / At BDC /
Travel TDC to BDC BDC to TDC TDC to BDC BDC to TDC
IV, EV condition IVO / EVC IVC / EVC IVC / EVC IVC / EVO

Action inside Air is sucked inside Air is compressed Pressure and Burnt gases are
cylinder the cylinder through & Fuel is injected Temperature pushed out through
inlet valve opening end of stroke increases & push exhaust valve
combustion begins down the piston opening

At the end of
stroke
Piston position At BDC At TDC At BDC At TDC

IV, EV condition IVC / EVC IVC / EVC IVC / EVO IVO / EVC

Crank shaft
rotation

52
53
P-V Indicator diagram

54
 Two Stroke SI Engine
The two stroke engine only requires two piston movements (2 stroke / 1
revolution of crankshaft) in order to generate power.
The engine is able do produce power after one cycle because the exhaust
and intake of the gas occurs simultaneously.

Suction & Compression stroke: The inlet port opens, the air-fuel mixture
enters the chamber and the piston moves upwards compressing this mixture.
A spark plug ignites the compressed fuel and begins the power stroke.
Power & Exhaust stroke: The heated gas exerts high pressure on the
piston, the piston moves downward (expansion), waste heat is exhausted.

55
2-stroke S.I (petrol engine)

56
 Working of 2 Stroke SI Engine
Suction Stroke & Compression Stroke Power Stroke & Exhaust Stroke

Piston position / Travel At BDC / At TDC /

BDC to TDC TDC to BDC
IP, EP, TP condition IPO / EPC / TPC IPC / EPO / TPO

Action inside cylinder Air, Fuel mixture is sucked inside the Pressure and Temperature increases
crank case through inlet port opening. & push down the piston
A/F mixture is compressed & Spark is Induction of compressed air removes
ignited end of stroke combustion begins the products of combustion through

exhaust ports
-Transfer port is there to supply the
fresh charge into combustion
chamber
Crank shaft rotation

57
58
P-V Indicator diagram

59
 Two Stroke CI Engine
The two stroke engine only requires two piston movements (2 stroke / 1 revolution of
crankshaft) in order to generate power.
The engine is able do produce power after one cycle because the exhaust and intake of the
gas occurs simultaneously.

Suction & Compression stroke: The inlet port opens, the air enters the crankcase and
the piston moves upwards compressing this mixture. A fuel is injected the compressed
fuel and begins the power stroke.
Power & Exhaust stroke: The heated gas exerts high pressure on the piston, the piston
moves downward (expansion), waste heat is exhausted.

60
2-stroke C.I (Diesel engine)

61
 Working of 2 Stroke CI Engine
Suction Stroke & Compression Stroke Power Stroke & Exhaust Stroke

Piston position / Travel At BDC / At TDC /

BDC to TDC TDC to BDC
IP, EP, TP condition IPO / EPC / TPC IPC / EPO / TPO

Action inside cylinder Air is sucked inside the crank case Pressure and Temperature increases
through inlet port opening. & push down the piston
A is compressed & fuel is injected end Induction of compressed air removes
of stroke combustion begins the products of combustion through
exhaust ports
-Transfer port is there to supply the
fresh charge into combustion
chamber
Crank shaft rotation

62
63
64
65
 Comparison between 4 stroke and 2 stroke engine
Specification Four-stroke engine Two-stroke engine
No of piston strokes per cycle 1. Four stroke of the piston require to Two stroke of the piston require to
complete one cycle complete one cycle
Revolution of crankshaft Two revolution of crankshaft complete Only one revolution of
one cycle
Crankshaft complete one cycle
Power One power stroke in every two revolution One power stroke in each revolution of
of crankshaft. Crankshaft.

Power produce is less Theoretically power produce is twice than

the four-stroke engine for same size

Number of power strokes per Equal to speed of engine crank shaft (n=N)
min
Flywheel Heavier flywheel due to non-uniform Lighter flywheel due to more uniform
turning movement turning movement
Admission of charge The charge is directly admitted into the The charge is first admitted into the
engine cylinder crankcase and then transfer to the engine
cylinder

Crank shaft rotation Crank shaft rotates in only one direction Rotates in both direction
Size for same power output Heavy, bulky and more space Light, compact and less space 66
 Comparison between 4 stroke and 2 stroke engine
Specification Four-stroke engine Two-stroke engine
Cooling and Lubrication Lesser cooling and lubrication Greater cooling and lubrication
requirements requirements
Wear and Tear Lesser rate of wear and tear Higher rate of wear and tear

Valves Contains valves and valves are operated Contains ports arrangement and ports are
by valve mechanism operated by piston itself
Initial cost Higher initial cost Cheaper initial cost
Volumetric efficiency Volumetric efficiency is more due to Volumetric efficiency less due to lesser
greater time of induction time of induction
Thermal efficiency Thermal efficiency is high Thermal efficiency is low because there
is mixing of fresh charge with exhaust
gas
Mechanical efficiency Low, because more number of moving High, because a smaller number of
parts moving parts
Application It is used where efficiency is important. It is used where low cost, compactness

Ex-cars, buses, trucks, tractors, industrial and light weight are important.
engines, aero planes, power generation
Ex-scooters, motor cycles, mopeds,
etc. 67
propulsion ship etc.
 Comparison between SI and CI engine
SI engine CI engine

Thermodynamic cycle Working cycle is Otto cycle / constant Working cycle is diesel cycle / constant
volume cycle. pressure cycle.
Fuel is used Petrol or gasoline or high octane fuel is Diesel or high cetane fuel is used.
used.

Self-ignition temperature High self-ignition temperature. Low self-ignition temperature.

Charge supply Fuel and air introduced as a gaseous Fuel is injected directly into the
mixture in the suction stroke. combustion chamber at high pressure at
the end of compression stroke.

Fuel supply Carburettor used to provide the mixture. Injector and high pressure pump used to
Throttle controls the quantity of mixture supply of fuel. Quantity of fuel
introduced. regulated in pump.

Fuel ignition Use of spark plug for ignition system Self-ignition by the compression of air
which increased the temperature
required for combustion then fuel is
68
sprayed start to burning
 Comparison between SI and CI engine
SI engine CI engine
Compression ratio Compression ratio is 6 to 10.5 Compression ratio is 14 to 22

Governing Quantity governing method is used for Quality governing method is used for
controlling speed controlling speed
Engine speed High speed about 3000 rpm. Low to medium

Thermal efficiency Thermal efficiency is lower due to Higher efficiency due to higher
lower compression ratio compression ratio

Weight of engine Lighter Heavier due to higher pressures &

temperature generate.

cost Low initial cost and high running cost High initial cost and low running cost

Maintenance cost Low Slightly higher

Starting of engine Starting is easy difficult
Fuel waste Fuel is wasted in scavenging process Fuel is not wasted 69