Which of the following is NOT one of the four strokes in a piston engine?

In a piston engine, the four fundamental strokes are intake, compression, power (or combustion), and exhaust. Each stroke represents a distinct phase in the engine cycle that allows it to convert fuel into mechanical energy.

The intake stroke involves drawing air and fuel into the cylinder, while the compression stroke compresses this mixture to prepare it for ignition. Following this, the combustion occurs, and in a traditional context, this phase is often simply referred to as the power stroke, where the ignition of the air-fuel mixture pushes the piston down. Finally, the exhaust stroke expels the burnt gases from the cylinder, making way for the next cycle.

Ignition, although essential to the process, does not stand alone as a stroke in this context; rather, it occurs during the power stroke when the air-fuel mixture is ignited, leading to the expansion of gases that drive the piston. Therefore, ignition is not classified as one of the four distinct strokes in the piston engine cycle.