In which engine stroke does the piston create a vacuum to draw in air and fuel?

The intake stroke is the phase in the four-stroke engine cycle during which the piston moves down the cylinder, creating a vacuum. As the piston descends, the intake valve opens, allowing air and fuel to be drawn into the combustion chamber through the reduction of pressure. This vacuum effect is essential for the proper functioning of internal combustion engines, as it enables the engine to intake the necessary mixture of air and fuel to create an explosive reaction during the power stroke.

In contrast, during the exhaust stroke, the piston moves upward to expel the combustion gases. The compression stroke involves the piston moving upward to compress the air-fuel mixture before ignition, and the power stroke is where the mixture is ignited and expands, pushing the piston down to generate power. Understanding the role of each stroke in the engine cycle helps in grasping how engines operate and the importance of the intake stroke in setting up the conditions for combustion.