What occurs during the intake stroke of a four-stroke engine?

During the intake stroke of a four-stroke engine, the intake valve opens, allowing the piston to move down in the cylinder. This downward movement creates a vacuum that draws in the air-fuel mixture through the open intake valve. This process is crucial as it fills the combustion chamber with the necessary mixture for combustion in the subsequent compression stroke.

The opening of the intake valve at this stage is essential because it provides a pathway for the air-fuel mix to enter the cylinder. Additionally, the downward movement of the piston reduces pressure in the cylinder, enhancing the intake process. Overall, this step is vital for preparing the engine to deliver power during the subsequent ignition and combustion strokes.

In contrast, other options refer to processes that do not happen during the intake stroke; for instance, the exhaust valve opening occurs during the exhaust stroke, and simply moving down with valves closed describes a specific scenario not applicable to the intake stroke. The fuel injector's action would take place earlier in the cycle, as it is involved in preparing the air-fuel mixture before the intake stroke occurs.