What happens during the exhaust stroke?

During the exhaust stroke of an internal combustion engine, the piston moves upward in the cylinder after the power stroke has taken place. This upward movement pushes the burnt gases out of the combustion chamber and into the exhaust system.

While it's true that during the exhaust stroke, the exhaust valve is open to allow for the exit of these gases, the intake valve remains closed. This is critical because it prevents any fresh air-fuel mixture from entering the cylinder at this stage. Therefore, saying both valves are open does not accurately describe the event occurring during the exhaust stroke.

The correct description is that the piston is moving up as it pushes out the burnt gases. This is a crucial function in the four-stroke cycle, ensuring that the combustion chamber is cleared out before the next cycle begins, which involves drawing in fresh air-fuel mixture. Understanding this process is essential for maintaining engine efficiency and performance.