Combustion on modern automotive gasoline
engines occurs within a cylinder (like a soda
can) where the energy of combustion pushes
down on a piston attached to a rotating shaft,
similar to the way a bicycle pedal is pushed
down by your feet, and turning in a circle.
Each cylinder is like another pedal- the more
pedals the faster a bike can go. The same is
true with cars. This is why most 8 cylinder
engines make more power than 4 cylinder
engines. Modern cars have between 4 and 12
cylinders turning the engine.
The engine cylinder also
behaves like an air pump, the
one you might use to inflate a
bicycle tire. Air is sucked in
one side, squeezed, and
pushed out of the other side.
This same airflow happens
within an engine cylinder. The
intake valve opens to let air
(and fuel) into the cylinder and
the exhaust valve opens to let
the burned air and fuel out to
the exhaust. This occurs in a
specific sequence called the 4
stroke cycle (invented in 1867
for the history buffs).