What is the 4-stroke Diesel Engine?

 

Diesel Engine- 

The engines of heavy motor vehicles(like trucks, and buses), stationary power plants, big industrial units, and ships mostly operate on diesel cycles or constant pressure cycles. It was introduced by Dr. Rudolph Diesel in 1897. The diesel cycle differs from the otto cycle in one respect. The heat is added at constant pressure instead of at constant volume. Thus, it comprises two adiabatic processes, one constant pressure heat addition process, and one constant volume heat rejection process. Diesel cycle engines mostly use heavy oils. 

 

Diesel oil is the most common. In diesel cycle engines only air is compressed in the cylinder to a high pressure, and the temperature of this compressed air becomes sufficiently high to ignite fuel. Diesel is injected into the cylinder at the end of the compression stroke which itself ignites due to the high temperature of the compressed air. There is no spark plug in a diesel engine. 

 

4- Strokes- 

The diesel engine generates power in four strokes. The diesel engine is also called the compression ignition engine. The four strokes are- 

 

 

Suction : 

During the suction stroke, the piston moves down from the top-dead-center position. Air is sucked into the cylinder through the open inlet valve which closes at the end of this stroke. The exhaust valve remains closed during this stroke. 

 

 

Compression :

In the compression stroke, the piston moves from the bottom dead center position. The inlet and exhaust valves remain closed. The air is compressed in the cylinder with the upward movement of the piston. as the compression ratio in this engine is high, the air is finally compressed to a pressure as high as 40kh/cm at which its temperature is high as 100-degree celsius, enough to ignite the fuel. 

 

 

Power :

At the end of the compression stroke, the fuel(diesel) is injected into the hot compressed air where it starts burning maintaining the pressure constant. When the piston is near the top dead center, the fuel supply is cut-off. Theoretically, the fuel is injected at the end of the compression stroke and injection continued till the point of cut-off. The piston moves from the top dead center to the bottom dead center, and this stroke is called the constant pressure stroke. The hot gases now expand adiabatically to the bottom of the cylinder pushing the piston down. Both valves remain closed during this stroke. 

 

 

Exhaust :

In this stroke, the piston moves upward. The inlet valve remains closed and the exhaust valve opens. The greater part of the burnt gas escape because of its own expansion. The upward movement of the piston pushes the remaining gasses out through the open exhaust valve. The cycle is thus completed.