IC Engine
Engine or motor is a
device designed to convert one form of energy into mechanical energy. The
arrangement of different parts of four stroke spark ignition engine (Petrol
engine) and four stroke compression ignition engine (Diesel engine) is shown in
the figure below:
Figure: Four Stroke Petrol Engine
Figure: Outline of Diesel Petrol Engine
The purpose of each
part is described in short:
1. Cylinder
The
cylinder of IC engine is considered as main body of engine in which piston
reciprocates to develop power. It has to withstand very high pressure of about
70 bar and temperature of about 2200o C because there is direct
continuous combustion inside the cylinder. So its material should retain
strength at high temperatures without any deformation, should be good conductor
of heat and should be able to resist to wear and tear due to reciprocating
parts. Generally, ordinary cast iron is used but incase of heavy duty engines,
alloy steels are used.
2. Cylinder head
The
cylinder seals one end of the cylinder. It houses the inlet, spark plug and
exhaust valve through which the mixture of air and fuel is taken and burnt with
the help of spark produced by spark plug and burnt gases are exhausted to the
atmosphere from exhaust. A copper and asbestos gaskets are provided between the
cylinder and cylinder heat to obtain a gas tight joint.
3. Piston and piston rings
The
primary function of piston is to compress the air fuel mixture during
compression stroke and to transmit the gas force to the connecting rod and then
to the crank during power stroke. Generally, the piston of IC engine are made
up of cast iron, cast steel and aluminium alloy. Often piston is considered as
heart of the engine.
The
piston rings are placed in the circumferential grooves provided on the outer
surface of the piston. It gives gastight fitting between piston and cylinder
and prevents from the leakage of high pressurized gases. It is made from
special grade cast iron which can retains its elastic property at very high
temperatures. The upper piston rings are called compression rings and lower
piston rings are called the oiling or oil control rings.
4. Connecting rod
Connecting
rod joins piston with crank. It is usually a steel forging of circular,
rectangular, I, T, or H section and is highly polished for increased endurance
strength. Its small ends forms a hinge and pin joint with piston and its big
end is connected to the crank by crank pin. It has a passage for the transfer
of lubricants from the big end bearing to small end bearing also known as
gudgeon pin.
5. Crank and crankshaft
The
crankshaft is the backbone of the engine. The main function of crankshaft is to
take power produced by engine and transmit it to the output shaft. Both crank
and crankshafts are steel forged and machined to a smooth finish. Both are held
together with the help of key. Crankshaft is supported in the main bearings
held by engine block and has a heavy wheel, known as flywheel, to even out the
fluctuations of torque. The power required for any useful purpose is taken out
from crankshafts only.
6. Piston pin or Wrist pin
The
piston pin provides the bearing for the oscillating small end of the connecting
rod.
7. Inlet valve
This
valve is responsible for the injection of air fuel mixture into the cylinder
during suction stroke of the engine. It is controlled by cam shaft mounted on
top of it.
8. Exhaust valve
This
valve is responsible for the removable of burnt gases from the cylinder after
the power stroke. It is also controlled by cam shaft mounted on top of it.
9. Valve spring
It
is used to keep valves closer to each other.
10. Inlet manifold
It
is the path from where air fuel mixture is carried from carburetor to the
petrol engine.
11. Exhaust manifold
It
is the passage from which carries the exhaust gases from exhaust valve to the
atmosphere.
12. Cam shaft
The
function of cam shaft is to control the motion of intake and exhaust valves
through the cams, cams follower, push rods and rocker arm. The cam shaft is
driven positively from the crankshaft and is connected with timing chain.
13. Cam and cam follower
It
is made of a required profile to give desired motion to the valves through the
followers.
14. Push rod and rocker arm
Push
rod and rocker arm transmits the motion of cam to the valves. These links
together are also called valve gear.
15. Crank case
It
is the base which holds the cylinder and the crankshaft. It also serves as the
sump for lubricating oil.
16. Water jacket
It
serves as cooling device for the engine operating at high temperatures.
17. Bed plate
The
lower portion of the crank case is also known as the bed plate. For concrete
foundations, bed plates are hold the bed bolts.
18. Flywheel
It
is the wheel mounted on the crankshaft which stores the excess energy during
the power stroke and returns the energy into the other strokes and maintains a
fairly consant output torque on the crankshafts.
19. Governor
The
function of the governor is to regulate the air fuel mixture in case of petrol
engine and amount of fuel in case of diesel engine to maintain a constant speed
of the engine. It is run by a drive from the crankshaft.
20. Carburetor
The
function of carburetor is to supply the uniform mixture is air and fuel to the
cylinder of petrol engine through the intake manifold. The mass of mixture
entering the cylinder is controlled by the throttle valve.
21. Spark plug
The
function of spark plug is to ignite the air fuel mixture after completing the
compression in the petrol engine. It is generally mounted on the cylinder head.
This is not used in diesel engine.
22. Fuel pump
It
forces the fuel at high pressure through the fuel nozzle into the cylinder at
the end of compression stroke in diesel engine.
23. Fuel nozzle
The
function of fuel nozzle is to break up the liquid fuel into a fine spray as it
enters the cylinder for proper combustion. It is used in diesel engine.
YV Nitesh
13th Jan
2019
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