The spark ignition engine uses a highly volatile fuel, such as gasoline, which turns into vapour easily. The fuel is mixed with air before it enters in the combustion chamber, and forms a combustible air-fuel mixture. This mixture then enters the cylinder and gets compressed with the help of a piston. An electric spark is produced by the ignition system which ignites the combustible air-fuel mixture. The combustible gases burn and expand, which forces the piston downwards for generating power.