Chapter: Mechanical Engineering : Internal Combustion Engines
Four Stroke Cycle Petrol Engines
PETROL ENGINES
Classification of Petrol Engines
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Two Stroke cycle Petrol Engines
•
Four Stroke cycle petrol Engines
FOUR STROKE CYCLE PETROL ENGINES
Construction :
•
A piston reciprocates inside the cylinder
•
The piston is connected to the crank shaftby means
of a connecting rod and crank.
•
The inlet and exhaust valves are Mounted on the
cylinder head.
•
A spark is provided on the cylinderHead.
•
The fuel used is petrol
Four Stroke Petrol Engine-
Working
(a) Suction
Stroke (First Stroke of the Engine)
•
Piston moves down from TDC to BDC
•
Inlet valve is opened and the exhaust valve is
closed.
•
Pressure inside the cylinder is reduced below the
atmospheric pressure.
•
The mixture of air fuel is sucked into the
cylinder through the inlet valve.
(b) Compression
Stroke : (Second Stroke of the piston)
•
Piston moves up from BDC to TDC
•
Both inlet and exhaust valves are closed.
•
The air fuel mixture in the cylinder is
compressed.
(c) Working
or Power or Expansion Stroke: (Third Stroke of the Engine)
•
The burning gases expand rapidly. They exert an
impulse (thrust or force) on the piston. The piston is pushed from TDC to BDC
•
This movement of the piston is converted into
rotary motion of the crankshaft through connecting rod.
•
Both inlet and exhaust valves are closed.
(d) Exhaust
Stroke (Fourth stroke of the piston)
•
Piston moves upward from BDC
•
Exhaust valve is opened and the inlet valve is
closed.
•
The burnt gases are forced out to the atmosphere
through the exhaust valve (Some of the burnt gases stay in the clearance volume
of the cylinder)
•
The exhaust valve closes shortly after TDC
•
The inlet valve opens slightly before TDC and the
cylinder is ready to receive fresh charge to start a new cycle.
Summary :
•
Compression ratio varies from 5 to 8
•
The pressure at the end of compression is about 6
to 12 bar.
•
The temperature at the end of the compression
reaches 250o C to 350o C
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