What is the state of the intake valve during the compression stroke?

During the compression stroke of an engine, the intake valve is closed. This is crucial for the compression process because, at this stage, the piston moves upwards in the cylinder, compressing the air-fuel mixture that has been drawn in during the intake stroke. If the intake valve were open, the compressed mixture would escape, preventing the engine from building the necessary pressure and temperature required for efficient combustion.

The closed position of the intake valve ensures that as the piston reaches the top of the compression stroke, the air-fuel mixture is tightly sealed in the combustion chamber. This compression increases the density of the mixture, which is vital for an effective combustion process once the spark plug ignites it. Proper timing of the valve operation is essential for optimal engine performance.