Four stroke diesel engine

SUCTION STROKE: With the movement of the piston
from T.D.C. to B.D.C. during this stroke, the inlet valve
opens and the air at atmospheric pressure is drawn
inside the engine cylinder; the exhaust valve however
remains closed. This operation is represented by the
line 5-1

COMPRESSION STROKE : The air drawn at atmospheric
pressure during the suction stroke is compressed to
high pressure and temperature as the piston moves
from B.D.C. to T.D.C. Both the inlet and exhaust valves
do not open during any part of this stroke. This
operation is represented by 1-2

POWER STROKE OR EXPANSION STROKE : As the piston
starts moving from T.D.C to B.D.C, the quantity of fuel
is injected into the hot compressed air in fine sprays by
the fuel injector and it (fuel) starts burning at constant
pressure shown by the line 2-3.
At the point 3 fuel supply is cut off. The fuel is injected
at the end of compression stroke but in actual practice
the ignition of the fuel starts before the end of the
compression stroke. The hot gases of the cylinder
expand adiabatically to point 4. Thus doing work on the
piston.
EXHAUST STROKE : The piston moves from the B.D.C.
to T.D.C. and the exhaust gases escape to the
atmosphere through the exhaust valve. When the piston
reaches the T.D.C. the exhaust valve closes and the
cycle is completed.

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.