During the compression stroke of the engine, the spark plug generates a high-voltage electrical spark that ignites the air-fuel mixture in the cylinder. This ignition process initiates combustion, producing high-temperature, high-pressure gases that drive the piston downward.

The design and characteristics of the spark plug can influence the combustion process, impacting the engine's performance and efficiency. Different types of spark plugs may be used for various engine types to meet specific performance and combustion efficiency requirements.