The correct sequence of a four-stroke cycle gas engine is as follows:
- Intake stroke: The intake valve opens, and the piston moves downward, drawing in a mixture of air and fuel into the combustion chamber.
- Compression stroke: Both the intake and exhaust valves are closed, and the piston moves upward, compressing the air-fuel mixture in the combustion chamber.
- Power stroke: At the top of the compression stroke, the spark plug ignites the compressed air-fuel mixture, causing a controlled explosion. The explosion forces the piston back down, generating power that is transferred to the crankshaft.
- Exhaust stroke: Once the power stroke is complete, the exhaust valve opens, and the piston moves upward, pushing the burned gases out of the combustion chamber and into the exhaust system.
This sequence—intake, compression, power, and exhaust strokes—repeats continuously as the engine runs, allowing for the efficient conversion of fuel into mechanical energy.