In what phase is the piston moving down in a four-stroke engine?

In a four-stroke engine, the piston moves down during the intake stroke. This phase occurs after the compression stroke and before the power stroke. During the intake stroke, the intake valve opens, and as the piston moves downward in the cylinder, it creates a vacuum that allows air and fuel to be drawn into the combustion chamber.

The downward motion is crucial as it facilitates the entry of the air-fuel mixture, which is necessary for the subsequent combustion process that occurs during the power stroke. Understanding this phase is essential because it sets up the engine for the energy-producing cycle that follows.