Europe can be said to be a paradise for diesel vehicles, with German diesel vehicles accounting for 39%. Diesel vehicles have a history of nearly 70 years. In the last 10 years, diesel engines have developed by leaps and bounds. 1997, Bosch and Mercedes-Benz jointly developed a common rail diesel injection system. Nowadays, in Europe, many brands of cars are equipped with * * * rail diesel engines, such as Peugeot's HDI*** rail diesel engine, Fiat's JTD engine, and Delphi developed Multec DCR diesel * * * rail system.
* * * The rail system is different from the diesel injection system driven by camshaft. * * The common rail diesel injection system completely separates the generation of injection pressure from the injection process. The injector controlled by solenoid valve replaces the traditional mechanical injector. The fuel pressure in the fuel rail is generated by the radial plunger high-pressure pump, which has nothing to do with the engine speed and can be set freely within a certain range. * * * The fuel pressure in the rail is controlled by an electromagnetic pressure regulating valve, and the pressure is continuously adjusted according to the working needs of the engine. The pulse signal of the electronic control unit acting on the solenoid valve of the fuel injector controls the fuel injection process. The amount of fuel injected depends on the oil pressure in the fuel rail, the opening time of the solenoid valve and the liquid flow characteristics of the nozzle.
Injection pressure is an important index of diesel engine, because it is related to engine power, fuel consumption, emissions and so on. * * * The common rail diesel injection system increases the fuel injection pressure to 1800 bar.
In the past two years, cars equipped with direct injection diesel engines have developed significantly in Europe. They have high efficiency and excellent fuel economy, and reduce engine noise. Direct injection diesel engine adopts pump nozzle system, which is used by domestic 1.9TDI Bora, and the highest injection pressure can reach 1800 bar. Although the pump nozzle direct injection system is good, the fuel pressure cannot be kept constant. With the increasingly strict emission control, higher and constant diesel injection pressure and more perfect electronic control are needed, so many manufacturers take the more advantageous diesel common rail system as the development direction of diesel engines. The system has high fuel pressure and can provide flexible fuel distribution control. The electronic control unit can flexibly control fuel distribution, injection timing, injection pressure and injection rate. By controlling the above characteristics, the responsiveness and driving comfort of diesel engine reach the level of gasoline engine, and it has remarkable fuel economy and low emission characteristics.
Ensure high fuel pressure in all engine speed ranges, and high injection pressure can obtain good combustion characteristics at low speed.
In the axial plunger pump engine driven by camshaft, the fuel system pressure has a linear relationship with the engine speed, which leads to insufficient fuel pressure at low engine speed, while the * * * rail system can obtain high fuel pressure in all engine speed ranges. The flexible electronic control system can control timing and injection pressure to achieve low emission and high efficiency under various working conditions of the engine. Because the formation of pressure is separated from the injection process, engine designers have more freedom in studying the combustion and injection process. The injection pressure and injection timing can be adjusted according to the requirements of engine working conditions, so that the engine can achieve complete combustion at low speed, and thus great torque can be obtained even at very low speed. The application of pre-injection technology has made greater progress in reducing emissions and noise.