During which stroke does air and fuel enter the cylinder?

The intake stroke is the phase of the four-stroke engine cycle when the air-fuel mixture is drawn into the cylinder. During this stroke, the piston moves down the cylinder, creating a vacuum that allows the intake valve to open. As a result, atmospheric pressure forces the air-fuel mixture into the combustion chamber. This process is critical because it establishes the combustible mixture needed for the engine to run efficiently.

In contrast, during the exhaust stroke, the exhaust valves open, and the burnt gases are expelled from the cylinder. The compression stroke occurs next, where the piston moves back up to compress the air-fuel mixture, enhancing the potential energy for the combustion that will occur in the power stroke, which is when the actual work of engine power generation takes place. Understanding the correct function of the intake stroke is fundamental for grasping how internal combustion engines operate effectively.