21st Century Overview - Ignition

Ignition begins when the alternator produces an electric spark across the spark plug, which ignites the air/fuel mixture in each cylinder at the end of each compression stroke.

Spark Plug has an air gap between its two electrodes across which a high voltage creates a spark that ignites the compressed fuel-air (gasoline-oxygen) mixture.

Spark ignites the compressed gasoline and oxygen mixture.   This combustion produces expanding gases that push the piston to the bottom of its stroke.