Tag Archive Working principle of four stroke diesel engine

The work of the diesel engine is accomplished by the four processes of intake, compression, combustion expansion and exhaust. These four processes constitute a working cycle. A diesel engine with four cycles to complete a working cycle is called a four stroke diesel engine. Now compare the animation above to explain its work.
1. Intake stroke
The first stroke intake, its task is to make the cylinder full of fresh air. When the intake stroke begins, the piston is located at the TDC, and some exhaust gases are left in the combustion chamber.
When the crankshaft rotates the elbow, the connecting rod causes the piston to move from the TDC to the stop point, and at the same time, the intake valve is opened with the transmission mechanism connected with the crankshaft.
As the piston moves downward, the volume of the piston in the cylinder increases gradually: the air pressure inside the cylinder is lower than the pressure in the intake pipe, so the air outside is continuously filled into the cylinder.
The gas pressure in the cylinder varies with the volume of the cylinder during the intake process, as shown in the animation. The vertical coordinates in the figure represent the gas pressure P, and the abscissa coordinates the cylinder volume Vh (or the piston punching S). This figure is called indicator diagram. The pressure curve in the diagram shows the change rule of the gas pressure in the cylinder when the diesel engine works. From the soil we can see that the intake starts with residual gas, so it is slightly higher than atmospheric pressure P0. The air pressure in the intake stroke is lower than the atmospheric pressure in the intake process, so the gas pressure in the intake stroke is 0.085~0.095MPa, and the gas pressure in the cylinder is roughly constant during the whole intake process.
When the piston moves down to the bottom stop, the air flow in the cylinder is still very high, and the inertia is very high. In order to use the inertia of the air flow to increase the volume of air, the intake valve is closed after the piston has passed down the stop point. Although the piston is ascending, the gas can still be filled with a cylinder because of the inertia of the air flow.