Here's a breakdown of the four stages:
1. Intake: The piston moves down, creating a vacuum in the cylinder. This draws in a mixture of air and fuel (or just air in a diesel engine) through the intake valve.
2. Compression: The intake valve closes, and the piston moves up, compressing the air-fuel mixture.
3. Combustion: The spark plug ignites the compressed air-fuel mixture, causing a rapid expansion of hot gas. This expansion pushes the piston down.
4. Exhaust: The exhaust valve opens, and the piston moves up, pushing the burnt gases out of the cylinder.
So, intake is the very first step where the engine starts preparing for the combustion process.
