Respuesta :

the combustion happens when the gas hits the spark plugs in the the chamber where the heads are.
teddybear20099
 As the piston reaches the top of its stroke or TDC the spark plug fires igniting the mixture. Due to the high compression of this mixture (typically around 190 PSI in a typical engine) it is very volatile and it explodes when the spark is introduced. This pushs the piston downward and produces power.