1. First of all, under the action of external forces (driven by the starter), the piston is driven by the crankshaft for reciprocating motion. once the cylinder works, it can work by itself without external forces

2. When the piston moves from top to bottom, the intake valve opens and starts to realize the intake (mixture of gasoline car and pure air in diesel engine) -- intake

3, the piston from the bottom to the top of the movement, the inlet and exhaust valve closed, will just enter the air compression, and produce high temperature -- compression

4. At the end of compression, the mixed gas of the gasoline car is ignited by the spark plug, the high-temperature gas of the diesel car is injected by the fuel injector and burns by itself, and the gas in the cylinder expands sharply under the action of combustion, prompting the piston to go down -- to do work

5. When the piston moves from BDC to BDC, the exhaust valve opens to exhaust and prepare for the next cycle.