What is the working principle of diesel engine?

1 The working principle of the diesel engine

The working principle of the diesel engine is basically the same as that of the gasoline engine, and there are also four strokes, and work is done through the reciprocating motion of the piston. The main difference lies in the formation of combustible mixture and ignition methods, Table 10-6 shown in the diesel engine and gasoline engine differences. Diesel engines do not have a carburetor, the intake stroke only air through the intake valve into the cylinder. Since the compression ratio of a diesel engine is higher than that of a gasoline engine, the high pressure gas obtained is at a higher temperature.

Toward the end of the compression stroke, fuel is injected directly into the cylinder through the injector nozzles, and the high-pressure air mixes with the injected fuel, causing the fuel to self-ignite at high temperature and high pressure, a process that requires high pressure. The fuel injection speed and the mixing speed of fuel and air **** the same determines the combustion speed of the fuel. In order to avoid too much fuel entering at one time, resulting in high pressure in the cylinder, fuel can be continuously injected during the work stroke.

Gasoline engine through the position of the throttle valve to change the engine to do work, idle state, the throttle valve closed, only a small amount of air into the cylinder; output of work is larger, through the throttle valve into more air. And diesel engine in different work situation, the amount of air into the same, it is through the control of fuel injection to determine the engine speed and output work.

In a diesel engine, the fuel is injected into the combustion chamber, can not be completely mixed with the air, the center of the cylinder combustion state is rich in combustion, the area of combustion can not reach the cylinder wall. When the diesel engine is running at full load, the rich combustion area in the combustion chamber is larger, and there is a large excess of fuel, it will produce a lot of black smoke.

Diesel engines are categorized into direct injection and premixed according to their construction. Direct injection diesel engine center injector nozzle will be directly injected into the combustion chamber, the combustion chamber air and fuel mixing is not sufficient, there are rich and poor combustion zone. Pre-mixed diesel engine that is inter-injection diesel engine, fuel is not directly injected into the main cylinder, but in the main cylinder before the addition of a pre-mixing cylinder, where the fuel is first burned, the combustion of the gas through the connecting holes, into the main cylinder. This way of working, increasing the turbulence of the gas mixture, so that the fuel and air mix more fully, there is no excessive rich combustion area, reducing the formation of black smoke particles, most light diesel engines use premixed. But the process of gas expansion through the connection hole into the cylinder will lose some of the energy, reducing the efficiency of the engine.

2 Formation of pollutants in diesel engine emissions

The harmful components of diesel engine exhaust are mainly CO, HC, NOx, sulfides, and particulate matter (or particulate matter), and odor. As the diesel engine using the average air-fuel mixture than the theoretical air-fuel ratio is large, so its CO and HC emissions are significantly lower than gasoline engines, diesel engine NO emissions are almost comparable to gasoline engines, and particulate matter and obnoxious gases in the emissions are much higher than gasoline engines, the test proved that diesel engine particulate emissions up to gasoline engines up to 10 times the number of times. Diesel engine emission characteristics and the form of combustion chamber has a great deal to do with, especially direct injection and indirect injection diesel engine emissions have a big difference. Swirl combustion chamber diesel engine NO, CO, HC and smoke is generally lower than direct injection diesel engine, especially NOx emission concentration is generally lower than the direct injection diesel engine 1 / 3 ~ 1/2.

Structure of the same combustion chamber in different forms of combustion chamber and swirl combustion chamber diesel engine on the test results show that the direct injection of diesel engines, NO, CO, HC and smoke is higher than that of the swirl chamber, in particular, the NO, CO, HC and smoke. In particular, the differences in NO, CO, smoke at high load and CO and HC at low load are very obvious. However, the fuel consumption rate of the diesel engine with scroll chamber is higher than that of the direct injection diesel engine.