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With the increase in the number of construction machinery and transportation vehicles in various countries around the world, the exhaust gas emitted by diesel engines has become one of the main causes of pollution to the earth's environment. How to take measures to protect the earth's environment that humans rely on for survival has become a top priority. Since the 1980s, our country has formulated relevant standards accordingly, making environmental protection a major issue. At the same time, countries around the world have begun to look for and explore other methods and take other effective technical measures to proactively reduce and control pollutant emissions. Common rail electronically controlled fuel injection technology is a relatively successful new technology for controlling diesel engine pollution emissions that stands out from many methods and measures. When the diesel engine is running at high speed, the diesel injection process takes only a few thousandths of a second. Experiments have shown that during the injection process, the pressure everywhere in the high-pressure oil pipe changes with time and location. The compressible nature of diesel and the pressure fluctuation of diesel in the high-pressure oil pipe make the actual fuel injection state significantly different from the plunger fuel supply rule specified by the fuel injection pump. The pressure fluctuation in the oil pipe sometimes causes the pressure in the high-pressure oil pipe to rise again after the injection, reaching the pressure that opens the injector needle valve, and reopens the closed needle valve to cause secondary injection. Since the secondary injection of fuel cannot be completely burned, it increases smoke and hydrocarbon (HC) emissions and increases fuel consumption. In addition, the residual pressure in the high-pressure oil pipe will change after each injection cycle, causing unstable injection, especially in the low-speed region. In severe cases, not only the fuel injection will be uneven, but also intermittent non-injection will occur. In order to solve the defects caused by changes in fuel pressure of diesel engines, modern diesel engines use an electronic injection technology called "common rail". 1. Principle It is generally believed that diesel engine fuel injection technology has gone through two development stages: traditional purely mechanically controlled fuel injection and modern electronically controlled fuel injection. The rise of modern electronically controlled fuel injection technology is the result of the rapid development of computer technology and sensing detection technology. At present, electronically controlled fuel injection technology has developed from the initial position control type to the time control type. Common rail electronically controlled fuel injection technology belongs to the latter. Common rail EFI technology refers to a fuel supply method that completely separates the generation of injection pressure and the injection process in a closed-loop system composed of a high-pressure oil pump, a pressure sensor and an electronic control unit (ECU). It uses a high-pressure oil pump to deliver high-pressure fuel to the public oil supply pipe, and achieves precise control through the oil pressure in the public oil supply pipe, so that the pressure of the high-pressure oil pipe has nothing to do with the engine speed, which can greatly reduce the degree of change of the diesel engine oil supply pressure with the engine speed. Therefore, the defects of traditional diesel engines are reduced. The ECU controls the amount of fuel injected by the injector, which depends on the pressure of the fuel rail (common fuel supply pipe) and the opening time of the solenoid valve. This technology no longer uses the traditional principle of pulsating fuel supply by plunger pumps. Instead, it directly or indirectly forms constant high-pressure fuel through the supply rail and distributes it to each injector. With the help of the opening and closing of the high-speed electromagnetic switch valve integrated on each injector, it regularly and quantitatively controls the amount of oil injected by the injector into the diesel engine combustion chamber, thereby ensuring that the diesel engine achieves the best combustion ratio and good atomization, as well as the best ignition time, sufficient energy and minimal pollution emissions. The principle of the diesel engine rail-supplied electronically controlled fuel system is shown in the attached figure. 2. Classification According to the difference in high pressure formed by fuel injection, there are two basic types of common rail electronically controlled fuel injection systems, namely high pressure common rail type and medium pressure common rail type. (1) High-pressure common rail system. The high-pressure fuel pump (pressure above 120MPa) directly generates high-pressure fuel, then delivers it to the common rail to eliminate pressure pulsation, and then distributes it to each injector. ； When the electronic control device sends out a command signal as needed, the high-speed solenoid valve (response in about 200s) quickly opens or closes, thereby controlling the injector to inject or stop injecting high-pressure fuel according to the set requirements. (2) Medium voltage common rail system. The medium-pressure fuel transfer pump (pressure 10-13MPa) delivers medium-pressure fuel to the common rail to eliminate pressure pulsation, and then distributes it to the injector with a booster plunger. ； When the high-speed solenoid valve switch valve receives the command signal sent by the electronic control device, it quickly opens or closes to control the operation of the fuel injector. Through the boosting effect of the high-pressure plunger, the medium-pressure fuel from the common rail is pressurized to high pressure (120-150MPa) and then sprayed or stopped. The main difference between the high-pressure common rail system and the medium-pressure common rail system is that the high-pressure fuel is obtained in different ways. ； The former is directly provided by the high-pressure fuel pump, while the latter is obtained by boosting the fuel with the help of a booster plunger.