A diesel engine high-pressure common rail technology

The high pressure oil pump is provided with the fuel oil to the common supply pipe, and the fuel injection is directly injected into the cylinder through the control of the fuel injector. High pressure common rail injection process and the hydraulic pressure generated completely separate, so that the fuel supply pressure will not be affected by the engine speed.
1 the injection pressure flexibility in high pressure common rail system can be adjusted to determine the optimum injection pressure for different working conditions to optimize the overall performance of the diesel engine.
2 can be independently flexible control of injection timing, with high injection pressure (120MPa ~ 200MPa), can control the NOx and particulate (PM) in a smaller value, in order to meet the emission requirements.
3 flexible control of injection rate change, to achieve the ideal injection law, easy to achieve pre injection and multiple injection, both to reduce the diesel engine NOx, but also to ensure excellent power and economy.
4. By the electromagnetic valve control fuel injection, high control precision, high-pressure oil does not appear bubble and residual voltage is zero, so in the diesel engine operating range, small cycle fuel injection quantity changes, uneven of the cylinder oil can improve, so as to reduce the vibration of the diesel engine and reduce emissions.
Representative models:
At the end of 1999 the birth of the assembly with a total of 3 cylinder diesel engine Smart, its displacement is only 799mL, maximum power 30kW, the maximum torque of 1800 ~ 100Nm output 2800rpm.
Introduced Benz E320 installed the second generation common rail engine, the output torque of 250nm maximum power 150kW/1000rpm. In 1400rpm can get 85% of the peak torque, peak torque 500nm in the vast area of 1800 to 2600rpm. 0 ~ 100km/h acceleration time is only 7.7 seconds, the maximum speed of 243km/h. Integrated fuel consumption is 80L, 6.9L/100km fuel tank to make life reached 1000km. And the E320 is equipped with a gasoline engine fuel consumption is 9.9L/100km.
Technical summary:
In the diesel engine, the time of the diesel injection process is only a few seconds, the experiment shows that the pressure of the high-pressure oil pipe in the process of injection is different with the time and position. Due to the compression of the diesel oil and the pressure fluctuation of high pressure oil pipe, the actual fuel injection status and the fuel injection pump are different. The pressure fluctuations in the tubing and sometimes in the main jet, high-pressure pipeline pressure rise again, to make the injector needle valve opening pressure, will have closed the valve is opened again produced the phenomenon of secondary injection, due to the secondary injection can not be completely burn, to increased emissions of smoke and hydrocarbons (HC), increased fuel consumption. In addition, each spray cycle after the residual pressure in the high-pressure oil pipe will change, the consequent unstable injection, especially in the low speed region is prone to the phenomenon, not only when a serious injection uneven and occur intermittently do not spray phenomenon. In order to solve the problem of diesel engine fuel pressure change, the modern diesel engine uses a technology called common rail.
High pressure common rail technology is refers to the high-pressure oil pump, pressure sensor and the ECU is composed of the closed loop system, the injection pressure and injection process are totally separated from each other by a feed way, by a high pressure oil pump to high pressure fuel delivery to the public the oil supply pipe, through - public oil supply pipe of oil pressure to achieve precise control, the high pressure tubing size and engine speed has nothing to do, can greatly reduce diesel engine oil pressure changes with the speed of the engine, thereby reducing the defects of the traditional diesel engine. ECU to control the amount of fuel injection, fuel injection quantity depends on the fuel rail (common supply pipe) pressure and the length of the solenoid valve opening time.
Technical principle:
The high pressure common rail system is mainly composed of an electric control unit, a high pressure oil pump, a pressure accumulator (common rail), an electronically controlled injector and a variety of sensors. Low pressure fuel pump fuel input and high pressure pump, high pressure pump the fuel pressure into the high-pressure rail (accumulator), high pressure fuel rail pressure by the electronic control unit according to the fuel rail pressure sensor to measure the rail pressure and the need to adjust, high-pressure rail fuel through a high pressure oil pipe. According to the operation state of the machine, by the electronic control unit to determine appropriate injection timing, injection duration by the electro-hydraulic control of the electronic fuel injector will fuel is sprayed into the cylinder.
1 high pressure oil pump
The design criterion for the oil supply of the high pressure oil pump is to ensure that the fuel injection quantity of the diesel engine in any situation and the demand of the quantity and the quantity of oil change during starting and accelerating. Due to the fuel pressure in the common rail system on the fuel injection process is independent of production and injection timing nor by a high-pressure oil pump cam to ensure, so oil pressure of high-pressure oil pump cam can be in accordance with the lowest peak torque, the contact should be minimum force and the wear of the design principles to design the cam.
Most of the company's use of three cylinder driven by a diesel engine to the plunger pump to generate pressure up to 135MPa. The high pressure oil pump adopts a plurality of pressure oil cams in each pressure oil unit, the peak torque is reduced to the 1/9 of the traditional high pressure oil pump, the load is relatively uniform, and the operation noise is reduced. Through the cavity of the common rail fuel release to achieve the, in order to reduce the power loss, in a small amount of fuel injection, will close three cylinder plunger pump in a pressure oil unit to reduce the amount of oil to the system of high pressure common rail cavity pressure control.
2 high pressure oil rail (common rail)
Common rail fuel pump provides the pressure will be assigned to each injector, from the accumulator function. Its volume should be reduced by high-pressure oil pump