New Technology in Diesel Engines (2)

2. Common rail technology

In automobile diesel engines, the high-speed operation makes the diesel injection process only a few thousandths of a second. Experiments have shown that the pressure of the high-pressure oil pipe varies with time and location during the injection process. Due to the compressibility of diesel and the pressure fluctuation of diesel in the high-pressure oil pipe, the actual fuel injection state is quite 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 main injection, reaching the pressure that opens the needle valve of the fuel injector, and reopens the closed needle valve to produce a secondary fuel injection phenomenon. Since the secondary injection cannot burn completely, it increases smoke and hydrocarbon (HC) emissions, and fuel consumption increases. In addition, the residual pressure in the high-pressure fuel pipe will change after each injection cycle, which will cause unstable injection, especially in the low-speed area, which is prone to the above phenomenon. Phenomenon. In order to solve this problem of diesel engine's fuel pressure change, modern diesel engine adopts a technology called "common rail".

Common rail technology refers to a fuel supply method in which the generation of injection pressure and the injection process are completely separated from each other in a closed-loop system composed of a high-pressure fuel pump, a pressure sensor and an ECU. The precise control of the oil pressure in the common oil supply pipe makes the pressure of the high-pressure oil pipe independent of the engine speed, which can greatly reduce the change of the diesel engine oil supply pressure with the engine speed, thus reducing the defects of the traditional diesel engine. The ECU controls the fuel injection volume of the injector, and the fuel injection volume depends on the pressure of the fuel rail (common fuel supply pipe) and the length of the solenoid valve coil opening time.

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