What is the working process of a diesel engine?

[DeJuliana]

Due to the rotation of the crankshaft, the piston moves from the top dead center to the bottom dead center in the cylinder through the connecting rod, at which time the exhaust valve closes and the intake valve opens. The crankshaft continues to rotate, and the piston moves from the bottom dead center to the top dead center, at which time both the intake and exhaust valves are closed, forming a sealed volume in the cylinder. At this point, the intake and exhaust valves are closed, and the high-temperature and high-pressure gas expands rapidly, causing the crankshaft to rotate through the connecting rod, thereby performing external work.