I c engine

I.C.Engine
Prepare by:-
Shivkumar Panjabi
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Prepare by:-Shivkumar Panjabi

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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, heat engine can be classified as an internal
combustion engine and external combustion engine.
2Prepare by:-Shivkumar Panjabi

• In an Internal combustion engine, combustion takes
place within working fluid of the engine, thus fluid gets
contaminated with combustion products.
– Petrol engine is an example of internal combustion
engine, where the working fluid is a mixture of air
and fuel .
• In an External combustion engine, working fluid gets
energy using boilers by burning fossil fuels or any other
fuel, thus the working fluid does not come in contact with
combustion products.
– Steam engine is an example of external combustion
engine, where the working fluid is steam. 3Prepare by:-Shivkumar Panjabi

Internal combustion engines may be classified as :
– Spark Ignition engines.
– Compression Ignition engines.
• Spark ignition engine (SI engine): An engine in which the
combustion process in each cycle is started by use of an external
spark.
• Compression ignition engine (CI engine): An engine in which
the combustion process starts when the air-fuel mixture self
ignites due to high temperature in the combustion chamber
caused by high compression.
– Spark ignition and Compression Ignition engine operate
on either a four stroke cycle or a two stroke cycle.

• Four stroke cycle : It has four piston strokes over
two revolutions for each cycle.
• Two stroke cycle : It has two piston strokes over
one revolution for each cycle.
• We will be dealing with Spark Ignition engine and
Compression Ignition engine operating on a four
stroke cycle.

Internal combustion Engine Components:
I.C. Engine components shown in figure1 and figure2 are
defined as follows:
• Block : Body of the engine containing cylinders, made of cast iron or
aluminium.
• Cylinder : The circular cylinders in the engine block in which the
pistons reciprocate back and forth.
• Head : The piece which closes the end of the cylinders, usually
containing part of the clearance volume of the combustion chamber.
• Combustion chamber: The end of the cylinder between the head and
the piston face where combustion occurs.
– The size of combustion chamber continuously changes from
minimum volume when the piston is at TDC to a maximum
volume when the piston at BDC.

• Crankshaft : Rotating shaft through which engine work output is
supplied to external systems.
– The crankshaft is connected to the engine block with the main
bearings.
– It is rotated by the reciprocating pistons through the connecting
rods connected to the crankshaft, offset from the axis of
rotation. This offset is sometimes called crank throw or crank
radius.
• Connecting rod : 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.
• Piston rings: Metal rings that fit into circumferential grooves around
the piston and form a sliding surface against the cylinder walls.8Prepare by:-Shivkumar Panjabi

• Camshaft : Rotating shaft used to push open valves at the proper
time in the engine cycle, either directly or through mechanical or
hydraulic linkage (push rods, rocker arms, tappets) .
• Push rods : The mechanical linkage between the camshaft and
valves on overhead valve engines with the camshaft in the
crankcase.
• Crankcase : Part of the engine block surrounding the crankshaft.
– In many engines the oil pan makes up part of the crankcase
housing.
• Exhaust manifold : Piping system which carries exhaust gases
away from the engine cylinders, usually made of cast iron .

• Intake manifold :Piping system which delivers incoming air to the
cylinders, usually made of cast metal, plastic, or composite material.
– In most SI engines, fuel is added to the air in the intake manifold
system either by fuel injectors or with a carburetor.
– The individual pipe to a single cylinder is called runner.
• Carburetor : A device which meters the proper amount of fuel into
the air flow by means of pressure differential.
– For many decades it was the basic fuel metering system on all
automobile (and other) engines.
• Spark plug : Electrical device used to initiate combustion in an SI
engine by creating high voltage discharge across an electrode gap.

• 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.
• Flywheel : Rotating mass with a large moment of inertia connected
to the crank shaft of the engine.
– The purpose of the flywheel is to store energy and furnish
large angular momentum that keeps the engine rotating
between power strokes and smooths out engine operation.
I.C. Engine components apart from
components shown in the figure:

• Fuel injector : A pressurized nozzle that sprays fuel into the
incoming air (SI engines )or into the cylinder (CI engines).
• Fuel pump : Electrically or mechanically driven pump to
supply fuel from the fuel tank (reservoir) to the engine.
• Starter : Several methods are used to s start IC engines. Most
are started by use of an electric motor (starter) geared to the
engine flywheel. Energy is supplied from an electric battery.

Figure3 : Engine Terminology

Figure 3, shows the pressure volume diagram of ideal engine cycle
along with engine terminology as follows:
• Top Dead Center (TDC): Position of the piston when it stops at the
furthest point away from the crankshaft.
– Top because this position is at the top of the engines (not
always), and dead because the piston stops as this point.
Because in some engines TDC is not at the top of the
engines(e.g: horizontally opposed engines, radial
engines,etc,.) Some sources call this position Head End Dead
Center (HEDC).
– Some source call this point TOP Center (TC).
– When the piston is at TDC, the volume in the cylinder is a
minimum called the clearance volume.
Engine Terminology :

• Bottom Dead Center (BDC): Position of the piston when it stops at
the point closest to the crankshaft.
– Some sources call this Crank End Dead Center (CEDC)
because it is not always at the bottom of the engine.Some
source call this point Bottom Center (BC).
• Stroke : Distance traveled by the piston from one extreme position
to the other : TDC to BDC or BDC to TDC.
• Bore :It is defined as cylinder diameter or piston face diameter;
piston face diameter is same as cylinder diameter( minus small
clearance).
• Swept volume/Displacement volume : Volume displaced by the
piston as it travels through one stroke.
– Swept volume is defined as stroke times bore.
– Displacement can be given for one cylinder or entire engine
(one cylinder times number of cylinders).

• Clearance volume : It is the minimum volume of the cylinder
available for the charge (air or air fuel mixture) when the piston
reaches at its outermost point (top dead center or outer dead center)
during compression stroke of the cycle.
– Minimum volume of combustion chamber with piston at
TDC.
• Compression ratio : The ratio of total volume to clearance volume
of the cylinder is the compression ratio of the engine.
– Typically compression ratio for SI engines varies form 8
to 12 and for CI engines it varies from 12 to 24

SI Engine Ideal Otto Cycle
• We will be dealing with four stroke SI
engine, the following figure shows the
PV diagram of Ideal Otto cycle.

Figure4: Suction stroke

Suction/Intake stroke: Intake of air fuel mixture in cylinder
through intake manifold.
– The piston travel from TDC to BDC with the intake valve
open and exhaust valve closed.
– This creates an increasing volume in the combustion
chamber, which in turns 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
carburettor.
Four strokes of SI Engine Cycle :

Figure5: Compression Stroke

• Compression stroke: When the piston reaches BDC, the
intake valve closes and the piston travels back to TDC
with all valves closed.
– This compresses air fuel mixture, raising both the
pressure and temperature in the cylinder.
– Near the end of the compression stroke the spark
plug is fired and the combustion is initiated.

• 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
before TDC and lasts into the power stroke slightly after
TDC.
– Combustion changes the composition of the gas mixture to
that of exhaust products and increases the temperature in
the cylinder to a high value.
– This in turn increases the pressure in the cylinder to a high
value.

Figure6: Combustion followed by Expansion stroke.

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

• Exhaust Blowdown : Late in the power stroke, the exhaust valve is
opened and exhaust blowdown occurs.
– Pressure and temperature in the cylinder are still high
relative to the surroundings at this point, and a pressure
differential is created through the exhaust system which
is open to atmospheric pressure.
– This pressure differential causes much of the hot exhaust
gas to be pushed out of the cylinder and through the
exhaust system when the piston is near BDC.
– This exhaust gas carries away a high amount of enthalpy,
which lowers the cycle thermal efficiency.
– Opening the exhaust valve before BDC reduces the work
obtained but is required because of the finite time needed
for exhaust blowdown.

Figure7: Exhaust blowdown followed by Exhaust stroke

• Exhaust stroke: By the time piston reaches BDC, exhaust
blowdown is complete, but the cylinder is still full of exhaust gases
at approximately atmospheric pressure.
– With the exhaust valve remaining open, the piston travels
from BDC to TDC in the exhaust stroke.
– This pushes most of the remaining exhaust gases out of the
cylinder into the exhaust system at about atmospheric pressure,
leaving only that trapped in the clearance volume when the
piston reaches TDC.

– Near the end of the exhaust stroke before TDC, the
intake valve starts to open, so that it is fully open by
TDC when the new intake stroke starts the next cycle.
– Near TDC the exhaust valve starts to close and finally is
fully closed sometime after TDC.
– This period when both the intake valve and exhaust valve
are open is called valve overlap, it can be clearly seen in
valve timing chart given below.

Compression Ignition Engine :
• We will deal with Compression Ignition
engine.
• The ideal diesel cycle PV diagram is shown
in following figure 8.

Figure8: Ideal diesel cycle P-V Diagram.

Figure9: Four strokes of ideal Diesel cycle.

Figure10:Suction stroke

Figure11: Compression stroke

• Intake/Suction Stroke : The same as the intake stroke in an SI
engine with one major difference : no fuel is added to the
incoming air, refer figure 10.
• Compression Stroke : The same as in an SI engine except that
only air is compressed and compression is to higher pressures and
temperature, refer figure11.
– Late in the compression stroke fuel is injected directly into
the combustion chamber, where it mixes with very hot air.
– This causes the fuel to evaporate and self ignite, causing
combustion to start.
» Combustion is fully developed by TDC and continues at about
constant pressure until fuel injection is complete and the piston
has started towards BDC, refer figure12.
Four strokes of CI Engine Cycle :

Figure12:Fuel injection and combustion followed by Expansion stroke .

Figure13: Exhaust stroke followed by exhaust blowdown.

• Expansion/Power stroke : The power stroke
continues as combustion ends and the piston travels
towards BDC, refer figure 12.
– Exhaust blowdown same as with an SI engine.
• Exhaust stroke : Same as with an SI engine, refer
figure 13.

Internal Combustion Engines
– four stroke -
Advantages:
•dedicated lubrication system makes to engine
more wear resistant
•better efficiency that 2-stroke engine
•no oil in the fuel – less pollution
Drawbacks:
•complicated constriction
•should work in horizontal position due to
lubrication

– two stroke -
1. Power / Exhaust 2. Intake / Compression
a. ignition
b. piston moves downward
compressing fuel-air mixture in
the crankcase
c. exhaust port opens
a. inlet port opens
b. compressed fuel-air mixture
rushes into the cylinder
c. piston upward movement
provides further compression

– two stroke -
Advantages:
•lack of valves, which simplifies construction and
lowers weight
•fire once every revolution, which gives a
significant power boost
•can work in any orientation
•good power to weight ratio
Drawbacks:
•lack of a dedicated lubrication system makes
the engine to wear faster.
•necessity of oil addition into the fuel
•low efficiency
•produce a lot of pollution

I c engine

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