Diesel engine works are as follow:
1. In a diesel engine ignition is achieved by compression of air alone. A typically compression ratio for a diesel engine is 20:1.
2. A diesel engine always draws in the air same amount of air (at each engine speed) through an throttled inlet track that is open and close only by the inlet valve( there is neither of carburator nor a butterfly valve).
3. When the Piston reaches the effective end of its induction stroke, the inlet valve closes. The Piston, carried around by the power from the other Pistons and the monument of the flywheel, travels to the top of the cylinder, compressing the air into about a twentieth of its volume.
4. As the Piston reaches the top of its travel, a precisely metered quantity of diesel fuel is injected into the combustion chamber. The heat from compression fires the fuel air mixture immediately, causing it to burn and expand. This forces the Piston downward, turning the crankshaft.
5. As the Piston moves up the cylinder on the exhaust stroke, the exhaust valve opens and allows the burned and expand gases to travel down the exhaust pipe. At the end of the exhaust stroke the cylinder is ready for a fresh charge of air.