What is the action of the exhaust valve during the power stroke?

During the power stroke of an internal combustion engine, the exhaust valve remains closed. This is crucial because the power stroke is the phase where the combustion of the air-fuel mixture occurs, producing high pressure that drives the piston down. If the exhaust valve were opened during this phase, it would allow the combustion gases to escape prematurely, significantly reducing the engine's efficiency and power output. Keeping the exhaust valve closed ensures that all the energy produced from the combustion is utilized to move the piston and generate power, maximizing the engine's performance. Thus, the closed position of the exhaust valve is essential for proper engine operation during the power stroke.