Basic Working Principle Of Two Stroke Diesel Engine Of Diesel Generator Set

Basic working principle of two-stroke diesel engine:

Two stroke diesel engine: a diesel engine that uses two strokes and the crankshaft rotates for one cycle.

The difference between a two-stroke diesel engine and a four stroke diesel engine is that the cylinder is equipped with an air port, the right side of the cylinder is an exhaust port, and the left side is an inlet port. The air inlet is slightly lower than the exhaust port, and the piston controls the opening and closing of the air inlet. In addition, the two-stroke diesel engine is equipped with scavenging pump. The compressed air is sent to the scavenging box in advance by the scavenging pump, and the air pressure (scavenging pressure) in the scavenging box is slightly higher than the atmospheric pressure.

① The piston moves upward from the bottom dead center in the first compression stroke. Before the piston is close to the air inlet, the cylinder is continuously filled with fresh air and the exhaust gas in the cylinder is expelled through the exhaust port. When the air inlet is completely covered by the piston, fresh air no longer enters the cylinder. When the exhaust port is covered by the piston, the piston compresses the air in the cylinder to produce high pressure and high temperature gas. At a certain time before the piston reaches TDC, diesel fuel is injected into the cylinder by the fuel injector and ignited after mixing with high-temperature and high-pressure air.

In this stroke, the air exchange, compression and fuel injection ignition combustion processes are completed.

② The piston moves downward from top dead center during expansion - air exchange stroke. The mixture is still burning fiercely at the beginning of this journey. The piston works downward due to gas expansion. When the exhaust port is opened in the downward direction of the piston, the pressure and temperature of the gas in the cylinder are still high at this time, which are 0.25~0.6MPa and 600~800 ° C respectively. Under the action of the rated pressure difference between the inside and outside of the cylinder, the gas in the cylinder is discharged from the exhaust port at a high speed, and the pressure in the cylinder decreases accordingly. When the falling pressure in the cylinder is close to the scavenging pressure, the downward piston opens the air inlet, fresh air enters the cylinder through the air inlet, and the cylinder is purged to exhaust the exhaust gas in the cylinder. This process is called scavenging process, and it will continue until the next cycle piston goes up again and closes the air inlet.

In this stroke, the combustion and expansion, exhaust and partial scavenging processes are completed.

It can be seen that compared with the four stroke diesel engine, the two stroke diesel engine combines the intake and exhaust processes into the compression and expansion stroke, and two strokes are omitted. Therefore, the two-stroke diesel engine completes one cycle of crankshaft rotation. With the same piston stroke, cylinder diameter and speed, the power of a two-stroke diesel engine seems to be twice that of a four stroke diesel engine. However, in fact, the power of a two-stroke diesel engine is about 1.6~1.8 times that of a four stroke diesel engine due to the reduction of its effective stroke due to the air port and other reasons.

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