1. Engine
Any machine that converts one form of
energy into useful mechanical energy is
termed as engine.

2. Efficiency
• Volumetric Efficiency
• Combustion Efficiency
• Thermal Efficiency

3. • Volumetric Efficiency: The ‘volumetric efficiency’
represents the degree of completeness with
which the cylinder is re-charged with fresh
combustible mixture and varies with different
engines and also with the speed.
• Combustion Efficiency: The ‘combustion
efficiency’ represents the degree of completeness
with which the potential heat units in the charge
are produced as actual heat in the cylinder.
• Thermal Efficiency: The ‘thermal efficiency’
governs the percentage of the actual heat units
present in the cylinder which are converted into
mechanical work.

4. Horsepower
• Indicated horse power
• Brake horse power

5. • Indicated Horse Power
Let,
p = mean effective pressure, N/m2.
D = diameter of cylinders, m.
L = length of stroke, m.
N = revolutions per minute.
f = no. of effective strokes, per revolution per
cylinder.
n = number of cylinders.

8. Definitions
• Top dead Centre : Position of the piston when it
stops at the furthest point away from the
crankshaft
• Bottom Dead Centre : Position of the piston when
it stops at the point closest to the crankshaft
• Bore : Diameter of the cylinder or diameter of the
piston face, which is the same minus a very small
clearance
• Stroke : Movement distance of the piston from
one extreme position to the other: TDC to BDC or
BDC to TDC

9. Definitions
• Indirect Injection : Fuel injection into the
secondary chamber of an engine with a
divided combustion chamber.
• Direct Injection : Fuel injection into the main
combustion chamber of an engine. Engines
have either one main combustion chamber
(open chamber) or a divided combustion
chamber made up of a main chamber and a
smaller connected secondary chamber.

10. Definitions
• Displacement volume : Volume displaced by
the piston as it travels through one stroke.
Also known as swept volume.
• Clearance volume : Minimum volume in the
combustion chamber with piston at Top Dead
Centre.

11. Definitions
• Ignition Delay : Time interval between ignition
initiation and the actual start of combustion
process.
• Wide-Open Throttle : Engine operated with
throttle valve fully open when maximum
power and/or speed is desired.

12. Definitions
• Compression Ratio: It is the ratio of the
volume of the combustion chamber or the
cylinder at the bottom dead center to the
volume of the combustion chamber at the top
dead center.
i.e.
Cr=VBDC/VTDC

13. Classification of Engines
• Internal combustion
• External combustion

14. Internal combustion Engine
• It is a heat engine that converts chemical
energy in a fuel into mechanical
energy, usually made available on a rotating
output shaft.
• Chemical energy Heat energy
Mechanical Energy

15. Classification of Internal combustion
Engines
• Type of stroke
• Type of ignition
• Type of design
• Relative position of cylinders
• Valve Location
• Type of Fuel used
• Air intake process
• Method of Fuel Input

16. Type of stroke
• Four-Stroke Cycle. A four-stroke cycle
experiences four piston movements over two
engine revolutions for each cycle.
• Two-Stroke Cycle. A two-stroke cycle has two
piston movements over one revolution for
each cycle.
• Six-Stroke Cycle.

17. Type of ignition
• Spark Ignition (SI). An SI engine starts the
combustion process in each cycle by use of a
spark plug. The spark plug gives a high-voltage
electrical discharge between two electrodes
which ignites the air-fuel mixture in the
combustion chamber surrounding the plug.
• Compression Ignition (CI). The combustion
process in a CI engine starts when the air-fuel
mixture self-ignites due to high temperature in
the combustion chamber caused by high
compression.

18. Type of design
• Reciprocating. Engine has one or more
cylinders in which pistons reciprocate back
and forth. Power is delivered to a rotating
output crankshaft by mechanical linkage with
the pistons.
• Rotary. Engine is made of a block (stator) built
around a large non-concentric rotor and
crankshaft. The combustion chambers are
built into the non-rotating block.

19. Relative position of Cylinders
Single Cylinder
In-Line
V Engine
W engine
Opposed Cylinder Engine
Opposed piston Engine
Radial engine

20. Single Cylinder. Engine has
one cylinder and piston
connected to the
crankshaft.

21. • In-Line. Cylinders are
positioned in a straight
line, one behind the
other along the length
of the crankshaft. They
can consist of 2 to 11
cylinders or possibly
more. In-line four-
cylinder engines are very
common for automobile
and other applications.

22. • V Engine. Two banks of
cylinders at an angle with
each other along a single
crankshaft. The angle
between the banks of
cylinders can be
anywhere from 15° to
120°, with 60°-90° being
common. V engines have
even numbers of
cylinders.

23. Opposed Cylinder Engine.
Two banks of cylinders
opposite each other on a
single crankshaft (a V
engine with a 180°V).
These are common on
small aircraft and some
automobiles. These
engines are often called
flat engines.

24. Sample Problem
• What is the difference between opposed
cylinder and V-cylinder configuration?

25. • W Engine. Same as a V
engine except with three
banks of cylinders on the
same crankshaft. Not
common, but some have
been developed for racing
automobiles, both modern
and historic. Usually 12
cylinders with about a 60°
angle between each bank.

26. Opposed Piston Engine.

27. • Two pistons in each cylinder with the
combustion chamber in the center between
the pistons.
• A single-combustion process causes two
power strokes at the same time, with each
piston being pushed away from the center and
delivering power to a separate crankshaft at
each end of the cylinder.
• Engine output is either on two rotating
crankshafts or on one crankshaft incorporating
complex mechanical linkage.

28. Valve Location
• Valves in head
• Valves in block
• One valve in head and one in block

29. Valve in block, L head.
Older automobiles and some small engines.

30. Valve in head, I head. Standard
on modern automobiles.

31. One valve in head and one valve in block, F
head. Older, less common automobiles.

32. Valves in block on opposite sides of
cylinder, T head.

33. Type of Fuel used
• Gasoline.
• Diesel Oil or Fuel Oil.
• Gas, Natural Gas, Methane.
• LPG.
• Alcohol-Ethyl, Methyl.

34. Air Intake Process
• Naturally Aspirated. No intake air pressure
boost system.
• Supercharged. Intake air pressure increased
with the compressor driven off of the engine
crankshaft.
• Turbocharged. Intake air pressure increased
with the turbine-compressor driven by the
engine exhaust gases

35. Supercharger

36. Turbocharger

37. Method of Fuel Input
• Carbureted.
• Multipoint Port Fuel Injection. One or more
injectors at each cylinder intake.
• Throttle Body Fuel Injection. Injectors
upstream in intake manifold.

38. Engine Operation Cycle
• Two stroke cycle
• Four stroke cycle

39. Two Stroke Cycle
• Compression Stroke
• Expansion Stroke

40. First Stroke
With all valves (or ports)
closed, the piston travels
towards TDC and
compresses the air-fuel
mixture to a higher
pressure and
temperature. Near the
end of the compression
stroke, the spark plug is
fired; by the time the
piston gets to IDC,
combustion occurs and
the next engine cycle
begins.

41. Combustion
occurs very quickly,
raising the
temperature and
pressure to peak
values, almost at
constant volume.

42. Second Stroke
Very high pressure
created by the
combustion process
forces the piston down
in the power stroke. The
expanding volume of the
combustion chamber
causes pressure and
temperature to decrease
as the piston travels
towards BDC.

43. Exhaust Blow down
At some point bBDC, the
exhaust valve opens and blow
down occurs. The exhaust
valve may be a poppet valve
in the cylinder head, or it may
be a slot in the side of the
cylinder which is uncovered
as the piston approaches
BDC. After blow down the
cylinder remains filled with
exhaust gas at lower
pressure.

44. Intake and Scavenging
At some point bBDC, the intake
slot on the side of the cylinder is
uncovered and intake air-fuel
enters under pressure.
This incoming mixture pushes
much of the remaining exhaust
gases out the open exhaust valve
and fills the cylinder with a
combustible air-fuel mixture, a
process called scavenging.
The piston passes BDC and very
quickly covers the intake port and
then the exhaust port. The higher
pressure at which the air enters
the cylinder is established in one
of two ways: supercharger and
crankcase.

45. Four stroke cycle
• Intake stroke or Induction
• Compression
• Expansion stroke or Power Stroke
• Exhaust Stroke

46. First Stroke
The piston travels from TDC to
BDC with the intake valve open and
exhaust valve closed. This creates an
increasing volume in the combustion
chamber, which in turn creates a
vacuum. The resulting pressure
differential through the intake
system from atmospheric pressure
on the outside to the vacuum on the
inside causes air to be pushed into
the cylinder. As the air passes
through the intake system, fuel is
added to it in the desired amount by
means of fuel injectors or a
carburetor.

47. Second Stroke
When the piston reaches BDC,
the intake valve closes and the
piston travels back to TDC with
all valves closed. This compresses
the air-fuel mixture, raising both
the pressure and temperature in
the cylinder. The finite time
required to close the intake valve
means that actual compression
doesn't start until sometime
aBDC. Near the end of the
compression stroke, the spark
plug is fired and combustion is
initiated.

48. Combustion
Combustion of the air-fuel mixture
occurs in a very short but finite
length of time with the piston near
TDC (i.e., nearly constant-volume
combustion). It starts near the end
of the compression stroke slightly
bTDC and lasts into the power
stroke slightly aTDC. Combustion
changes the composition of the gas
mixture to that of exhaust products
and increases the temperature in
the cylinder to a very high peak
value. This, in turn, raises the
pressure in the cylinder to a very
high peak value.

49. Third Stroke
With all valves closed, the high
pressure created by the
combustion process pushes the
piston away from TDC. This is
the stroke which produces the
work output of the engine
cycle. As the piston travels from
TDC to BDC, cylinder volume is
increased, causing pressure and
temperature to drop.

50. Exhaust Blow Down
The exhaust valve is opened and
exhaust blow down occurs. A
pressure differential is created
through the exhaust system which is
open to atmospheric pressure
causing much of the hot exhaust gas
to be pushed out of the cylinder and
through the exhaust system when
the piston is near BDC. Opening the
exhaust valve before BDC reduces
the work obtained during the power
stroke but is required because of the
finite time needed for exhaust blow
down.

51. Fourth Stroke
By the time the piston reaches BDC,
exhaust blow down is complete, but the
cylinder is still full of exhaust gases.
With the exhaust valve remaining open,
the piston now travels from BDC to TDC
in the exhaust stroke. This pushes most
of the remaining exhaust gases out of
the cylinder, leaving only that trapped in
the clearance volume when the piston
reaches TDC.
Near the end of the exhaust stroke
bTDC, the intake valve starts to open, so
that it is fully open by TDC when the new
intake stroke starts. Near TDC the
exhaust valve starts to close and finally is
fully closed sometime aTDC. This period
when both the intake valve and exhaust
valve are open is called valve overlap.

52. CI engine

53. Difference between SI and CI Engine
• Type of fuel used
• Type of cycle used
• Introduction of the fuel - In SI, through
carburetor/fuel injectors in intake stroke and
in CI through fuel pump in combustion stroke.
• Introduction of the air - In CI turbochargers or
superchargers are used where as there is no
such thing in SI engines.

54. • Ignition of fuel - Petrol is a highly volatile
liquid, but its self-ignition temperature is high.
Hence for the combustion of this fuel spark is
necessary to initiate its burning process.
• With diesel, the self-ignition temperature is
comparatively lower. When diesel fuel is
compressed to high pressures, its temperature
also increases beyond the self-ignition
temperature of the fuel. Hence in the case of
CI engines, the ignition of fuel occurs due to
compression of the air-fuel mixture and there
is no need for sparkplugs.

55. • Compression Ratio for the case of SI
engines, the compression ratio of the fuel is in
the range of 6 to 10 depending on the size of
the engine and the power to be produced. In
CI engines, the compression ratio for air is 16
to 20. The high compression ratio of air
creates high temperatures, which ensures the
diesel fuel can self-ignite.
• Weight of the engines
• Speed achieved by the engine
• Thermal efficiency of the engine

56. • Air Fuel Ratio: The air-fuel mixture is
homogeneous throughout in SI while in CI
engines only air enters and mixture is
heterogeneous in the cylinder.
• Engine Strength: Compression ignition engine
has to be built much stronger than an spark
ignition engine due to the fact that the
Compression Ignition engine will "Detonate" the
fuel and will cause it to explode . This is why
diesel engines are so much louder than gas
engines. Spark Ignition system ignites the fuel
and it burns in a rapid but controlled manner that
“Pushes" the piston down during the power
stroke and puts less stress on engine parts.

57. Sample Problem
• Write 2 advantages of two stroke engine over
four stroke engines and 2 advantages of four
stroke engines over two stroke engines

58. Detonation in SI Engine
• During the combustion of the fuel through spark plug, the end
charge auto-ignites itself before the flame front reaches it, hence
this abnormal combustion is called detonation or knocking.
• Auto-ignition occurs at a very critical temperature and the time
required by the fuel to reach this temperature is called ignition-
delay.
• In auto-ignition, the burning is almost instantaneous which results
in extremely rapid release energy and hence causing the pressure
of the end gases to rise to almost 3 to 4 times.
• This large pressure differential gives rise to severe pressure wave
which strikes the cylinder wall and sets it vibrating, giving high
pitched metallic pinking or ringing sound.
• To avoid this, a fuel should have high auto-ignition temperature and
long ignition-delay in SI engine.

59. Engine Problems
• Three fundamental things can happen:
– A bad fuel mix
– Lack of compression
– lack of spark
• Beyond that, thousands of minor things can
create problems, but these are the "big
three." Based on the simple engine we have
been discussing, here is a quick rundown on
how these problems affect your engine:

60. Bad Fuel Mix
• You are out of gas, so the engine is getting air but
no fuel.
• The air intake might be clogged, so there is fuel
but not enough air.
• The fuel system might be supplying too much or
too little fuel to the mix, meaning that
combustion does not occur properly.
• There might be an impurity in the fuel (like water
in your gas tank) that makes the fuel not burn.

61. Lack of Compression
• If the charge of air and fuel cannot be
compressed properly, the combustion process
will not work like it should. Lack of
compression might occur for these reasons:
• Your piston rings are worn (allowing air/fuel to
leak past the piston during compression).
• The intake or exhaust valves are not sealing
properly, again allowing a leak during
compression.

62. Lack of spark
• The spark might be nonexistent or weak for a
number of reasons:
• If your spark plug or the wire leading to it is worn
out, the spark will be weak.
• If the wire is cut or missing, or if the system that
sends a spark down the wire is not working
properly, there will be no spark.
• If the spark occurs either too early or too late in
the cycle, the fuel will not ignite at the right
time, and this can cause all sorts of problems.

63. • Many other things can go wrong. For example:
– If the battery is dead, you cannot turn over the engine
to start it.
– If the bearings that allow the crankshaft to turn freely
are worn out, the crankshaft cannot turn so the
engine cannot run.
– If the valves do not open and close at the right time or
at all, air cannot get in and exhaust cannot get out, so
the engine cannot run.
– If someone sticks a potato up your tailpipe, exhaust
cannot exit the cylinder so the engine will not run.
– If you run out of oil, the piston cannot move up and
down freely in the cylinder, and the engine will seize.

64. Constructional Details
• Block
• Cylinder Head
• Camshaft
• Crankshaft
• Cylinder
• Piston
• Connecting rods

65. Constructional Details
• Piston Rings
• Spark Plug
• Exhaust system
• Fuel pump
• Fuel Injector
• Water Jacket
• Radiator

66. Constructional Details
• Glow Plug
• Valves
• Smart Engine
• Catalytic Converter

67. • Engine block
Body of engine containing the cylinders, made of
cast iron or aluminum.

68. Cylinder Head
• The piece which closes the end of the cylinders,
usually containing part of the clearance volume
of the combustion chamber.
• It is usually cast iron or aluminum, and bolts to
the engine block.
• The head contains the spark plugs in SI engines
and the fuel injectors in CI engines and some SI
engines.
• Most modern engines have the valves in the
head, and many have the camshaft(s) positioned
there also (overhead valves and overhead cam).

70. Camshaft
• Rotating shaft used to push open valves at the
proper time in the engine cycle, either directly
or through mechanical or hydraulic linkage.
• Camshafts are generally made of forged steel
or cast iron and are driven off the crankshaft
by means of a belt or chain.
• In four-stroke cycle engines, the camshaft
rotates at half engine speed.

71. Camshaft

72. Crankshaft
• Rotating shaft through which engine work
output is supplied to external systems.
• The crankshaft is connected to the engine
block.
• It is rotated by the reciprocating pistons
through connecting rods connected to the
crankshaft.
• Most crankshafts are made of forged steel,
while some are made of cast iron.

73. Crankshaft

74. Cylinder
• Portion of engine block in which the pistons
reciprocate back and forth.
• The walls of the cylinder have highly polished
hard surfaces.
• Cylinders may be machined directly in the engine
block, or a hard metal sleeve may be pressed into
the softer metal block.
• Sleeves may be dry sleeves, which do not contact
the liquid in the water jacket, or wet sleeves,
which form part of the water jacket.

75. Cylinder

76. Piston
• The cylindrical-shaped mass that reciprocates
back and forth in the cylinder, transmitting the
pressure forces in the combustion chamber to
the rotating crankshaft.
• The top of the piston is called the crown and
the sides are called the skirt.
• Pistons are made of cast iron, steel, or
aluminum.

77. Connecting Rods
• Rod connecting the piston with the rotating
crankshaft, usually made of steel or alloy
forging in most engines but may be aluminum
in some small engines.

78. Piston & Connecting Rods

79. Piston Rings
• Metal rings that fit into circumferential grooves
around the piston and form a sliding surface
against the cylinder walls.
• Piston rings are made of highly polished hard
chrome steel.
• The purpose of these is to form a seal between
the piston and cylinder walls and to restrict the
high-pressure gases in the combustion chamber
from leaking past the piston into the crankcase.

80. Piston rings
Ride in grooves in piston head to seal the cylinder
TYPES
Compression rings : Prevent pressure leakage into
the crankcase.

81. Piston Rings
• Oil Rings : Prevent engine oil leakage to
combustion chamber

82. Piston Rings

83. Piston Assembly

84. Spark Plug
• Electrical device used to initiate combustion in
an SI engine by creating a high-voltage
discharge across an electrode gap.
• Spark plugs are usually made of metal
surrounded with ceramic insulation.

85. Spark Plug

86. Exhaust System
• Flow system for removing exhaust gases from
the cylinders, treating them, and exhausting
them to the surroundings.
• It consists of an exhaust manifold which
carries the exhaust gases away from the
engine, a thermal or catalytic converter to
reduce emissions, a muffler to reduce engine
noise, and a tailpipe to carry the exhaust gases
away from the passenger compartment.

87. Exhaust System

88. Fuel Injector
• A pressurized nozzle that sprays fuel into the
incoming air on SI engines or into the cylinder
on CI engines.
• On SI engines, fuel injectors are located at the
intake valve ports on multipoint port injector
systems and upstream at the intake manifold
inlet on throttle body injector systems.
• In a few SI engines, injectors spray directly into
the combustion chamber

89. Fuel Injector

90. Fuel Pump
• Pump to supply fuel from the fuel tank
(reservoir) to the engine.
• Many modern automobiles have an electric
fuel pump mounted submerged in the fuel
tank.
• Some small engines and early automobiles
had no fuel pump, relying on gravity feed.

91. Fuel Pump

92. Water Jacket
• System of liquid flow passages surrounding
the cylinders, usually constructed as part of
the engine block and head.
• Engine coolant flows through the water jacket
and keeps the cylinder walls from overheating.
• The coolant is usually a water-ethylene glycol
mixture.

93. Water jacket

94. Radiator
• Liquid-to-air heat exchanger of honeycomb
construction used to remove heat from the
engine coolant after the engine has been
cooled.
• The radiator is usually mounted in front of the
engine in the flow of air as the automobile
moves forward.
• An engine-driven fan is often used to increase
air flow through the radiator.

95. Radiator

96. Glow Plug
• Small electrical resistance heater mounted
inside the combustion chamber of many CI
engines.
• It is used to preheat the chamber enough so
that combustion will occur when first starting
a cold engine.
• The glow plug is turned off after the engine is
started.

97. Valves
• Used to allow flow into and out of the cylinder
at the proper time in the cycle.
• Most engines use poppet valves, which are
spring loaded closed and pushed open by
camshaft action.
• Valves are mostly made of forged steel.
• Valve seats and are made of hardened steel or
ceramic.

98. Valve

99. Smart engine
• Engine with computer controls that regulate operating
characteristics such as air-fuel ratio, ignition timing,
valve timing, exhaust control, intake tuning, etc.
• Computer inputs come from electronic, mechanical,
thermal, and chemical sensors located throughout the
engine.
• In automobiles the same computers are used to make
smart cars by controlling the steering, brakes, seats,
anti-theft systems, sound systems, navigation, noise
suppression, environment etc.
• On some systems engine speed is adjusted at the
instant when the transmission shifts gears, resulting in
a smoother shifting process.

100. Catalytic Converter
• It is the chamber mounted in exhaust flow
containing catalytic material that promotes
reduction of emissions by chemical reaction.
• Inside a catalytic converter, a catalyst stimulates
a chemical reaction in which noxious byproducts
of combustion carbon monoxide, unburned
hydrocarbons, and oxides of nitrogen are
converted to less-toxic or inert substances such
as carbon dioxide, hydrogen, nitrogen and
oxygen.

102. Engine Emissions
• One of the biggest problem with the
automobiles.
• Can’t be completely normalized.
• Compromises have to be done with the power
to decrease the emissions.

103. Emissions
• Hydrocarbons
• Carbon Monoxide
• Oxides of Nitrogen (NOx)

104. • Hydrocarbons are fuel molecules which did
not get burned and smaller non-equilibrium
particles of partially burned fuel.
• Carbon monoxide occurs when not enough
oxygen is present to fully react all carbon to
CO2 or when incomplete air-fuel mixing occurs
due to the very short engine cycle time.
• Oxides of nitrogen are created in an engine
when high combustion temperatures cause
some normally stable N2 to dissociate into
monatomic nitrogen N, which then combines
with reacting oxygen.

105. Prevention
• To improve the technology of engines and fuels
so that better combustion occurs and fewer
emissions are generated.
• The second method is after treatment of the
exhaust gases. This is done by using thermal
converters or catalytic converters that promote
chemical reactions in the exhaust flow.
• These chemical reactions convert the harmful
emissions to acceptable CO2, H20, and N2.