Figure 7 The four-stroke operating principal applied to a diesel engine

1. Air Intake Rotation of the crankshaft drives a toothed belt which turns the camshaft, opening the intake valve. As the piston moves down, a vacuum is created, sucking fresh air into the cylinder, past the open intake valve.		2. Air Compression As the piston moves up, both valves are closed and the air is compressed about 23 times smaller than its original volume. The compressed air reaches a temperature of about 1650°F, far above the temperature needed to ignite diesel fuel.
3. Fuel Injection and Compression As the piston reaches the top of the stroke, the air temperature is at its maximum. A fine mist of fuel is sprayed into the prechamber, where it ignites and the flame front spreads rapidly into the combustion chamber. The piston is forced downward by the pressure (about 500 psi) of expanding gasses.		4.Exhaust As the energy of combustion is spent and the piston begins to move upward again, the exhaust valve opens and burned gasses are forced out past the open valve. As the piston starts down, the exhaust valve closes, intake valve opens, and the air intake stroke begins again.

Figure 7 The four-stroke operating principal applied to a diesel engine