What occurs during the fourth piston stroke in an engine?

During the fourth piston stroke in a typical four-stroke internal combustion engine, the piston goes up and the exhaust valve opens. This is known as the exhaust stroke.

At this stage, the piston is moving upward in the cylinder, which creates a decrease in pressure that facilitates the expulsion of the burnt gases from the combustion chamber into the exhaust manifold. As the piston reaches the top of its stroke, the exhaust valve opens, allowing the combustion gases to exit the cylinder. The timing of this process is crucial for optimizing engine efficiency and performance since it ensures that the chamber is clear of exhaust before the next intake stroke begins.

The other options describe events that do not accurately represent the fourth piston stroke: the intake valve closing occurs prior to the fourth stroke; the piston remaining stationary is not part of the typical working cycle of a four-stroke engine; and while the intake valve opens, this action occurs during the intake stroke, not the exhaust stroke. Understanding these sequences is fundamental in comprehending how internal combustion engines operate and the specific roles of each stroke in the cycle.