Four stroke cycle engine

FOUR-STROKE CYCLE ENGINES

1.Four Stroke Petrol engine.

2.Four Stroke Diesel engine.

1.FOUR STROKE PETROL ENGINE:-

The four stroke-cycles refers to its use in petrol
engines, gas engines, light, oil engine and heavy oil
engines in which the mixture of air fuel are drawn in the
engine cylinder. Since ignition in these engines is due to
a spark, therefore they are also called spark ignition

SUCTION STROKE::- In this Stroke the inlet valve opens
and proportionate fuel-air mixture is sucked in the
engine cylinder. Thus the piston moves from top dead
centre (T.D.C.) to bottom dead centre (B.D.C.). The
exhaust valve remains closed through out the stroke.

COMPRESSION STROKE:- In this stroke both the inlet
and exhaust valves remain closed during the stroke.
The piston moves towards (T.D.C.) and compresses the
enclosed fuel-air mixture drawn. Just before the end of
this stroke the operating plug initiates a spark which
ignites the mixture and combustion takes place at
constant pressure.

POWER STROKE OR EXPANSION STROKE:- In this stroke
both the valves remain closed during the start of this
stroke but when the piston just reaches the B.D.C. the
exhaust valve opens. When the mixture is ignited by the
spark plug the hot gases are produced which drive or
throw the piston from T.D.C. to B.D.C. and thus the
work is obtained in this stroke.

EXHAUST STROKE: This is the last stroke of the cycle.
Here the gases from which the work has been collected
become useless after the completion of the expansion
stroke and are made to escape through exhaust valve
to the atmosphere. This removal of gas is
accomplished during this stroke. The piston moves
from B.D.C. to T.D.C. and the exhaust gases are driven
out of the engine cylinder; this is also called
SCAVENGING.