What is the basic working cycle of a diesel engine?

The basic working cycle of a diesel engine consists of four strokes: intake stroke, compression stroke, power stroke, and exhaust stroke, as follows:

Intake stroke: During this stroke, the piston is driven by the crankshaft to move from top dead center to bottom dead center. At this point, the intake valve opens and the exhaust valve closes. As the piston descends, the volume inside the cylinder increases, creating a certain degree of vacuum, and air is drawn into the cylinder under atmospheric pressure. Due to the compression ignition nature of diesel engines, only air is drawn in to provide sufficient oxygen for the subsequent combustion process.

Compression stroke: After the intake stroke, the piston begins to move from bottom dead center to top dead center, and both the intake and exhaust valves are closed. The air inside the cylinder is compressed, and the pressure and temperature continue to rise. The compression ratio of diesel engines is usually higher, generally between 16-22, much higher than gasoline engines. This allows the air to reach a high pressure and temperature at the end of compression, creating conditions for the spontaneous combustion of diesel.

Power stroke: Near the end of the compression stroke, the fuel injector sprays high-pressure diesel into the cylinder in a mist form. Diesel quickly mixes with high-temperature and high-pressure air and self ignites, generating a large amount of heat energy, causing a sharp increase in pressure and temperature inside the cylinder. The high-temperature and high-pressure gas pushes the piston to move from top dead center to bottom dead center, and drives the crankshaft to rotate through the connecting rod, outputting mechanical energy externally. This is the key stroke for diesel engines to achieve energy conversion.

Exhaust stroke: After the power stroke is completed, the piston moves again from bottom dead center to top dead center. At this point, the exhaust valve opens and the intake valve closes, and the burned exhaust gas is discharged from the cylinder under the push of the piston. When the piston reaches the top dead center, the exhaust stroke ends and the exhaust gas is basically exhausted. Subsequently, the engine begins a new intake stroke, repeating this cycle to keep the engine running continuously.

Diesel engines convert the chemical energy of diesel into mechanical energy through the continuous cycle of these four strokes, providing power for various equipment and vehicles. The characteristic of its working cycle is to rely on the high temperature generated by compressed air to ignite diesel, which has the advantages of high thermal efficiency and high torque, and is widely used in fields such as automobiles, ships, and engineering machinery.