On the __________ stroke of an engine, the piston is going up, one valve is open and the other valve is closed and the fumes are leaving the cylinder.

The correct answer is that during the exhaust stroke of an engine, the piston moves upward in the cylinder, which creates a specific process where one of the valves (the exhaust valve) is open while the other valve (the intake valve) is closed. This allows the burned gases from the combustion process to exit the cylinder after the power stroke has occurred. As the piston rises, it effectively pushes out the exhaust fumes, ensuring that the cylinder is cleared of gases before the next intake stroke begins.

Understanding the function of the exhaust stroke is crucial in the cycle of an internal combustion engine. It's this stroke that prepares the cylinder for the next cycle of operation by clearing out remnants of combustion. Therefore, recognizing that the exhaust stroke distinctly involves the expulsion of gases while the piston moves up and one valve is open contributes to a clearer comprehension of engine mechanics and efficiency.