Question

what is an engine combustion stroke?
a) when the piston moves down drawing air and fuel into the cylinder.
b) when the piston moves up causing the air/fuel mixture to combust.
c) when the spark plug ignites and the piston is forced to the bottom of the cylinder.
d) when the piston moves up forcing the exhaust to combust.

Explanation:

In an engine's combustion stroke, the spark - plug ignites the air - fuel mixture, and the resulting explosion forces the piston down to the bottom of the cylinder. Option A describes the intake stroke, option B is incorrect as the piston moves down after ignition in the combustion stroke, and option D is incorrect as exhaust does not combust during a normal stroke and the piston moves up in the exhaust stroke to push out exhaust.

Answer:

C. When the spark plug ignites and the piston is forced to the bottom of the cylinder.