What happens to the exhaust valve during the compression stroke?

During the compression stroke of an internal combustion engine, the exhaust valve is closed. This closure is crucial because it ensures that any gases produced from the combustion process do not escape the combustion chamber. Instead, the piston moves upward in the cylinder, compressing the air-fuel mixture that was introduced during the intake stroke. The increased pressure and temperature from this compression prepare the mixture for ignition.

The integrity of this seal, provided by the closed exhaust valve, allows the engine to build the necessary pressure to create an efficient combustion event when the spark plug ignites the compressed mixture. If the exhaust valve were to be opened or partially opened during this phase, it would result in a loss of pressure and a decrease in engine efficiency, leading to potential misfires and reduced power output. Therefore, keeping the exhaust valve closed is essential for optimal engine performance during the compression process.