This document provides information on internal combustion engines, including: 1. It defines internal combustion engines and classifies them based on where combustion occurs, fuel used, thermodynamic cycle, number of strokes, ignition method, cooling method, and more. 2. It describes the basic components of an IC engine like the cylinder block, cylinder head, piston, connecting rod, crankshaft, and camshaft. 3. It explains the four strokes of a typical four-stroke engine cycle and compares it to the two-stroke engine cycle.

1. Module 5

2. Total 18 Marks Theory 10 marks Numerical” 8

3. 5.1 Introduction to IC Engines and its Classification
Engine refers as “Heat engine is a device which converts chemical energy of fuel
into Heat energy and this Heat energy further convert into mechanical work”.
Based on where the combustion of fuel take place. Whether outside the working
cylinder or inside the working cylinder
(a) External combustion engines (E.C.ENGINES),
In EC engines, comb
•External Combustion of fuel takes place outside the working cylinder.
Examples: Steam Engines and Steam turbines
(b) Internal combustion engines (I.C.ENGINES)
•Internal Combustion Engines (IC Engines)
In IC engines, combustion of fuel takes place
inside the engine cylinder. Examples: Diesel Engines, Petrol Engines, Gas

4. IC Engines have efficiency about 35-40% EC Engines have efficiency about 15-20%

5. I.C ENGINE TERMINOLGOGY
The standard terms used in I.C Engines are
1. Bore: Inside diameter of the cylinder is termed as Bore.
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.
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.
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.
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

7. Classification of IC Engines
I.C.ENGINES are may be classified according to
• Type of fuel used as (1)Petrol engine (2)Diesel engine (3)Gas engines (4)Bi-fuel engine (two fuel engine)
• Nature of thermodynamic cycle as: (1)Otto cycle engine (Constant volume cycle) (2)Diesel engine cycle (Constant
pressure cycle) (3) Duel or mixed cycle engine (Semi Diesel cycle)
• Number of stroke per cycle as : (1) Four stroke engine (2) Two stroke engine
• Method of ignition as : (1) Spark Ignition engines (Mixture of air and fuel is ignited by electric spark)
(2) Compression Ignition engines (The fuel is ignited as it comes in contact with hot Compressed air)
(3) Hot spot ignition engines
• Method of Cooling as : (1) Air cooled engines (2) Water cooled engines
• Speed of the engines as : (1) Low speed engines (2) Medium speed engines (3) High speed engines
• Number of cylinder as : (1) Single cylinder engines (2) Multi cylinder engines
• Position of the cylinder as : (1) Inline engines (2) V-engines (3) Radial engines (4) Opposed cylinder engines
(4) Opposed piston engines Inline

8. Cylinder Block:
•It is the main block of the engine.
•It contains cylinders accurately finished to accommodate pistons
•The cylinder block houses crank, camshaft, piston and
other engine parts.
•In water cooled engines, the cylinder block is provided
with water jackets for the circulating cooling water.
•The materials used for cylinder are grey cast iron, aluminium alloys etc.,
•It is usually made of a single casting
Cylinder Head:
•The cylinder head is bolted to the cylinder Block by means of studs.
•The water jackets are provided for cooling water circulation.
•The materials used for cylinder head are cast iron, aluminium alloy etc.,
•This is also generally made of single cast iron.
Cylinder Liners:
The liner is a sleeve which is fitted into the cylinder bore.
It provides wear resisting surface for the cylinder bores.
Oil pan or oil sump:
Oil sump is the bottom part of the engine.It contains lubricating oil.A drain plug is provided
the oil sump to drain out the oil. It is made of the pressed sheet.

9. Piston :
The piston serves the following purposes
• It acts as a movable gas tight seal to keep the gases inside the cylinder
•It transmits the force of explosion in the cylinder to the crankshaft through the connecting
rod.
•Some of the materials used for piston are cast iron, aluminium alloy, chrome nickel alloy,
nickel iron alloy and cast steel
Piston rings :
Piston rings are inserted in the grooves provided in the piston. Two types of piston
rings are used in the piston.
1. Compression rings : provide an effective seal for the high pressure gases inside the cylinder.
2. Oil rings or oil control rings. : Oil rings wipe off the excess oil from the cylinder
walls.
Connecting Rod:
• It connects the piston and crank shaft. It transmits the force of explosion during power stroke to the
crankshaft. It has bearings at both ends.
• The small end of the connecting has a solid or split eye and contains a
bush. The other end is called as big end of the connecting rod.
• The connecting rods must withstand heavy thrusts. it must have strength and rigidity.
• They are usually drop forged I sections. The materials used are plain carbon steel, aluminum alloys, nickel
alloy steels etc,

10. Crank Shaft :
• It is the main rotating shaft of the engine. • Power is obtained from the crank shaft.
• The crank shaft is combination with connecting rod converts reciprocating motion of the piston into rotary
motion.
Camshaft:
• Camshaft contains number of cams.
• It is used to convert rotary motion into linear or straightline motion.
• It has so many cams as the number of valves in an engine.
• The opening and closing of the engine valves are controlled by the cams provided on the cam shaft.

11. Sequence of Operations in IC Engine
Each stroke in IC engines forms a sequence of operations in one cycle of IC Engines i.e
suction stroke, compression stroke, expansion stroke, and exhaust stroke.
The following sequence of operation in a cycle is widely used.
Suction stroke. In this stroke, the fuel vapor in correct proportion, is supplied to the engine cylinder.
Compression stroke. In this stroke, the fuel vapor is compressed in the engine cylinder.
Expansion or working stroke. In this stroke, the fuel vapor is fired just before the compression is complete. It results in
the sudden rise of pressure, due to expansion of the combustion products in the engine cylinder. This sudden rise of
pressure pushes the piston with a great force and rotates the crankshaft. The crankshaft, in turn, drives the machine
connected to it.
Exhaust stroke. In this stroke, the burnt gases (or combustion products) are exhausted from the engine cylinder, so as to
make space available for the fresh fuel vapor.

12. Two stroke and Four stroke cycle engines
A two-stroke (or two-stroke cycle) engine is a type of internal combustion engine that completes a power
cycle with two strokes (up and down movements) of the piston during one power cycle, this power cycle being
completed in one revolution of the crankshaft.
A four-stroke engine requires four strokes of the piston to complete a power cycle during two crankshaft
revolutions. In a two-stroke engine, the end of the combustion stroke and the beginning of the compression
stroke happen simultaneously, with the intake and exhaust (or scavenging) functions occurring at the same
time.
Because combustion takes place with each revolution of the crankshaft with a 2-stroke, this format puts
out more power than a 4-stroke engine and the power ...

13. Comparison Of 2 Stroke and 4 stroke

14. https://youtu.be/XKcRf2R5h4o

15. https://youtu.be/Pu7g3uIG6Zo

16. IS => Ignition Start
EVO => Exhaust Valve Open
EVC => Exhaust Valve Close
TDC => Top Dead Center
BOC => Bottom Dead Center.
The exact moment at which each of the valves opens and closes with reference to the position of piston and crank can be
shown graphically in a diagram. This diagram is known as “valve timing diagram”.
In theoretical valve timing diagram, inlet and exhaust valves open and close at both dead centers. Similarly, all processes
are sharply completed at TDC or BOC. Figure 1.72 shows theoretical valve timing diagram for four stroke SI engines
Figure 1.73 shows actual valve timing diagram for four stroke SI engine. The inlet valve opens 10-30° before TOC. The air-
fuel mixture is sucked into the cylinder till the inlet valve closes. The inlet valve closes 30-40°’ or ‘even 60° after BOC. The
charge is compressed till the spark occurs. The spark is produced 20-40° before TDC. It gives sufficient time for the fuel to
burn. Both pressure and temperature increase. The burnt gases are expanded till the exhaust valve opens.
Theoretical and Actual valve timing diagram For Four Stroke SI Engine

17. Theoretical valve timing diagram for the two-stroke cycle engine.
The theoretical valve timing diagram for a two-stroke cycle engine is shown. In this
diagram, the fuel is fired at A and the expansion of gases takes place from A to B.
The crankshaft revolves through approximately 120º and the piston moves from
T.D.C. towards B.D.C. At B, the valves open, and suction, as well as exhaust, take
place from B to C.
The crankshaft revolves through approximately 120º and the piston moves first to
B.D.C and then little upwards. At C. both the valves close and compression takes
place from C to A. The crankshaft revolves through approximately 120º and the
piston moves to T.D.C

23. Actual Cycles Losses The major losses are due to
1.Variation of specific heats with temperature
2.Dissociation of combustion products
3.Progressive combustion
4. Incomplete combustion of fuel
5.Heat transfer into the walls of the Cylinders
6.Blow down at the end of the exhaust process
7.Gas exchange process

27. Multipoint Fuel Injection System (MPFS)

30. Combustion and Knocking in SI Engine
https://youtu.be/EuHy_Vpx514

33. If detonation is allowed to persist under extreme conditions
or over many engine cycles, engine parts can be damaged or
destroyed. The simplest deleterious effects are typically
particle wear caused by moderate knocking, which may
further ensue through the engine's oil system and cause
wear on other parts before being trapped by the oil filter.
Such wear gives the appearance of erosion, abrasion, or a
"sandblasted" look, similar to the damage caused by
hydraulic cavitation. Severe knocking can lead to
catastrophic failure in the form of physical holes melted and
pushed through the piston or cylinder head (i.e., rupture of
the combustion chamber), either of which depressurizes the
affected cylinder and introduces large metal fragments, fuel,
and combustion products into the oil system. Hypereutectic
pistons are known to break easily from such shock waves.

34. Detonation can be prevented by any or all of the following
techniques:
retarding ignition timing
the use of a fuel with high octane rating, which increases the combustion
temperature of the fuel and reduces the proclivity to detonate enriching
the air–fuel ratio which alters the chemical reactions during combustion,
reduces the combustion temperature and increases the margin to detonation
reducing peak cylinder pressure
decreasing the manifold pressure by reducing the throttle opening or boost
pressure
reducing the load on the engine

36. PROBLEM 1
Data recorded during testing of a TWO STROKE
gas engine is
Diameter of the piston d= 150 mm
Stroke length L= 180 mm ,
Clearance volume Vc = 0.89 liter
RPM of the engine N = 300 ,
Indicated mean effective pressure pm= 6.1 bars
Gas consumption m. = 6.1 m3/h,
Calorific value of the gas (fuel) CF = 17000 kJ/m3
Determine the followings:
•Air Standard Efficiency
•Indicated power (IHP)developed by the engine
•Indicated thermal efficiency of the engine
SOLUTION
Swept volume Vs = πd2L/4
= π(0.150)2 x 180/4 = 0.00318 m3
Clearance volume Vc= 0.00089 m3
Total volume = Swept volume + clearance volume
VT = 0.00318 + 0.00089 = 0.00407 m3
Compression ratio γ = Total volume/Clearance volume
= 0.00407/0.00089 = 4.573
•Air standard Efficiency η = 1 –1/(r)γ—1
•= 1—1/(4.573)4—1
= 0.456 = 45.6 %
•Indicated power IHP = 100 p L AN/60 when p is in bars
= 100 x 6.1x 0.180 x [π(0.150)2/4] 300/60 = 9700 W
(c ) Indicated Thermal Efficiency
ηIT = Indicated power in (kJ/s)/Heat supplied in (kJ/s)
= (9700/1000)/(6.1 x 17000/3600) = 0.3367 = 33.67 %

37. PROBLEM 2
Following data is available for a
FOUR STROKE
petrol engine:
Air fuel ratio 15.5 : 1
Calorific value of fuel 16000 kJ/kg
Air Standard Efficiency: 53
Mechanical Efficiency: 80 %
Indicated Thermal Efficiency: 37 %
Volumetric Efficiency: 80 %
Stroke/bore ratio: 1.25
Suction pressure: 1 bar
Suction Temperature: 270C
RPM: 2000
Brake Power: 72 kW
Calculate the followings:
•Bore and stroke
•Find compression ratio from air standard
efficiency
SOLUTION
Find compression ratio from air standard efficiency
η = 1 –1/(r)γ—1
0.53 = 1 –1/(r)1.4—1
r = 6.6
•Bore and stroke of the engine
Mass of air fuel mixture/kg of fuel = 15.5 +1 = 16.5
Mass of fuel supplied to the engine = 0.0152 x 16.5 = 0.2508
Volume of air fuel mixture = mRT/p=0.2508x 287×300/(1×105)
V = 0.2159 m3/s
Swept volume = volume of mixture supplied/vol efficiency
Vs = 0.2159/0.80= 0.2699
Vs=( πd2L/4) n x (rpm/2) /60
Where n is the number of cylinders
= (πd2 x 1.25 d/4)n rpm/120
d= 0.152 m= 152 mm
L = 190 mm