Four-stroke
cycle operation in automobile engines is common nowadays. The four
strokes in the operation of a four-stroke cycle petrol engine are
suction stroke, compression stroke, power stroke and exhaust stoke.
The inlet valve should keep open and exhaust valve closed during
suction stroke. Downward movement of piston creates a partial vacuum
inside the cylinder. This leads to sucking of the mixture of air and
petrol into the cylinder. Both the inlet and exhaust valves are
closed during the compression stroke. The compressed mixture gets
vapourized and a spark is produced in the spark plug igniting the
mixture during this stroke. Inlet and exhaust valves remain closed
during power stroke. But the burning of gas forces exhaust valve to
open. During the exhaust stroke, the inlet valve is closed and the
exhaust valve is open. Here the burnt gas is pushed out of the
cylinder which forces exhaust valve to close and inlet valve open.
