What is the position of the valves and the movement of the piston during the exhaust event in a four-stroke engine?

During the exhaust event in a four-stroke engine, it is crucial to understand the synchronization between the valves and the piston movement. In this phase, the exhaust valve is open to allow the spent gases from combustion to exit the cylinder, while the intake valve remains closed to prevent any new air-fuel mixture from entering the cylinder.

As the piston moves upward during this event, it creates a negative pressure that helps push the exhaust gases out of the combustion chamber. This movement is essential for completing the cycle of the engine, preparing the cylinder for the next intake stroke.

The opening of the exhaust valve while the intake valve remains closed and the upward movement of the piston are key characteristics of the exhaust event in a four-stroke cycle. This process effectively clears the cylinder of leftover gases and sets the stage for the next cycle.