Which valve opens to draw the gas/air mixture into the cylinder?

The intake valve is responsible for allowing the gas/air mixture to enter the cylinder in an internal combustion engine. During the intake stroke of the engine cycle, the piston moves down, creating a vacuum that draws the air and fuel mixture into the cylinder through the intake valve. Once the piston reaches the bottom of its stroke, the intake valve closes, sealing the mixture in the cylinder for the next phase of the combustion process.

The exhaust valve, in contrast, opens after the combustion process to release the spent gases from the cylinder, while a compression valve is not a standard term used in engine design. Lastly, a release valve typically refers to a mechanism that releases pressure, rather than being involved in the intake of the fuel-air mixture. Thus, the intake valve plays a crucial role in preparing the engine for power generation by controlling the intake of gases into the combustion chamber.