GASOLINE ENGINES
Most automobiles use a four-stroke internal combustion gasoline engine. How
do these engines generate power? They have a four-stroke design, which means
that the pistons travel up and down four times in order to complete a power
cycle. Vital activity occurs during each stroke, ultimately producing the power
required to do the “work” of an automobile engine.
Intake Stroke
On the intake stroke, the camshaft opens the intake valve. At the beginning of
this stroke, the piston is at the top position. The fast downward travel of the
piston creates a vacuum, which sucks the air-fuel mixture into the combustion
chamber and fills it completely. Continuing its rotation, the camshaft then closes
the valves and seals the combustion chamber in preparation for the compression
stroke. When the piston has reached the bottom of its travel, its new position is
called BDC (bottom dead center).