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Method of Controlling Common Rail Fuel Injection Device

High pressure common rail

7/17/2017 8:41 AM
The high-pressure pump delivers the fuel to the common fuel supply pipe and injects the fuel directly into the tank by controlling the injector. The high pressure common rail separates the injection process from the oil pressure so that the oil supply pressure is not affected by the engine speed. The pressure in the high pressure common rail system is flexible and the optimum injection pressure can be determined for different working conditions, thus optimizing the comprehensive performance of the diesel engine. Flexible control of fuel injection rate changes, to achieve the ideal fuel injection law, easy to achieve pre-injection and multiple injection, can reduce the diesel engine NOx, but also to ensure excellent power and economy. (120MPa ~ 200MPa), can simultaneously control the NOx and particles (PM) in a smaller value to meet the emission requirements. By the solenoid valve control fuel injection, high control accuracy, high-pressure oil circuit will not appear in the bubble and residual voltage is zero phenomenon, so in the diesel engine operating range, the cycle of fuel injection changes in small, uneven supply of each cylinder can be Improve, thereby reducing the vibration of diesel engines and reduce emissions.
 
   High-pressure common rail technology refers to the high-pressure oil pump, pressure sensor and ECU composed of closed-loop system, the jet pressure generation and injection process are completely separated from each other a way of oil from the high-pressure pump to the high-pressure fuel to the public supply pipe, Through the precise control of the oil pressure in the common supply pipe, the pressure of the high pressure tubing is independent of the engine speed, which can greatly reduce the fuel supply pressure of the diesel engine with the engine speed change, thus reducing the traditional diesel engine defects. ECU control fuel injector fuel injection, the amount of fuel injection depends on the fuel rail (common fuel supply pipe) pressure and solenoid valve opening time.

  In diesel engines, high-speed operation makes the diesel injection process only a few thousandths of a second. Experiments show that the pressure across the high-pressure tubing varies with time and position during the injection process. Due to the compressibility of diesel oil and the pressure fluctuation of diesel oil in high pressure tubing, the actual fuel injection state is different from the fuel supply law stipulated in the fuel injection pump.

The pressure fluctuation in the tubing is sometimes increased again after the main injection, so that the pressure of the needle valve of the injector is turned on and the needle valve which has been closed is reopened to generate the secondary injection phenomenon, As the secondary fuel injection can not be completely burned, so increase the smoke and hydrocarbon emissions, fuel consumption increased. The residual pressure in the high-pressure tubing changes after each injection cycle, which causes unstable injection, especially in the low-speed area. This is not only the uneven fuel injection, but also the intermittent non-jetting phenomenon. In order to solve the diesel engine fuel pressure changes in the shortcomings of modern diesel engine used a technology known as common rail.

  High pressure common rail system is mainly composed of electronic control unit, high pressure oil pump, accumulator (common rail), electronically controlled injector and various sensors. Low-pressure fuel pump will be fuel input high-pressure oil pump, high-pressure oil pump will be fuel pressure into the high-pressure oil rail (accumulator), WeChat plus vehicle through the Shenzhen high pressure oil rail pressure by the electronic control unit according to the oil pressure sensor oil Rail pressure and the need to adjust the oil within the high-pressure oil rail through the high-pressure tubing, according to the operating state of the machine, by the electronic control unit to determine the appropriate fuel injection timing, fueling duration by the electro-hydraulic control of the electronic injector will fuel spray Into the cylinder.
  
   The design criteria for the oil supply of high pressure pumps is the need to ensure that the fuel injection capacity of the diesel engine in any case is equal to the sum of the fuel and the demand for fuel change during start-up and acceleration. Since the injection pressure Common Rail in the common rail system is independent of the fuel injection process and the fuel injection timing is not ensured by the cam of the high pressure pump, the high pressure oil pump can be operated at the lowest peak torque, minimum contact and wear resistance Design principles to design the cam.
     High pressure common rails are also equipped with pressure sensors, flow bumper (current limiter) and pressure limiter. Pressure sensor to the ECU to provide high-pressure oil rail pressure signal; flow buffer (current limiter) WeChat plus vehicle through Shenzhen to ensure that the fuel injector fuel leakage failure cut off the fuel supply to the injector, and can reduce Common rail and high pressure tubing pressure fluctuations; pressure limiter to ensure that the high pressure oil rail in the event of pressure anomalies, the rapid pressure in the high pressure oil rail discharge.

  The pressure in the high-pressure common rail chamber of the system is controlled by the discharge of fuel in the common rail chamber. In order to reduce the power loss, if the fuel injection is small, the three-cylinder radial piston A fuel oil unit in the pump reduces the fuel supply. The common rail pipe distributes the high pressure fuel supplied by the oil pump to each injector and acts as an accumulator. Its volume should be reduced Common Rail Nozzle by the high pressure pump oil pressure fluctuations and each injector by the fuel injection process caused by the pressure shock, so that high pressure oil rail pressure fluctuations in the control below 5MPa. But its volume can not be too large to ensure that the common rail has enough pressure to respond quickly to track the changes in diesel engine conditions.

'High pressure' refers to the fuel injection system pressure than the traditional diesel engine to 3 times higher, the maximum can reach 200MPa (while the traditional diesel fuel injection pressure in the 60-70 MPa), the pressure of large enough to burn a good combustion, thereby enhancing the power, And ultimately achieve the purpose of fuel-efficient. 'Common rail' is through the public supply pipe at the same time supply the various injectors, fuel injection through the ECU accurate calculation, while the various injectors to provide the same quality, the same pressure of fuel, the engine running more smoothly, so as to optimize the diesel engine Comprehensive performance. The traditional diesel engine fuel injection by the cylinder, fuel injection and pressure are inconsistent, uneven operation, resulting in combustion is not smooth, noise, high fuel consumption. Domestic manufacturing with the international advanced electronic control high-pressure common rail technology diesel engine using the latest European and American diesel engine technology, significantly better than the traditional supercharged diesel engine.
    Diesel common rail system has been developed for 3 generations, it has a strong technical potential. The first generation of common rail high pressure pumps are always kept at maximum pressure, resulting in energy waste and high fuel temperature. The second generation can change the output pressure according to the engine demand, and has the pre-injection and post-injection function. Pre-injection reduces engine noise: A small amount of fuel is blown into the cylinder before the main injection, and the preheated combustion chamber is injected. The preheated cylinder makes it easier to burn the main jet, and the pressure and temperature in the tank are no longer abruptly increasing, which is conducive to reducing the combustion noise. In the expansion process after the injection, resulting in secondary combustion, the cylinder temperature increased by 200 ~ 250 ℃, reducing the exhaust of hydrocarbons. Because of its strong technical potential, today the manufacturers have set their eyes Common Rail Injector on the common rail system 3rd generation - piezo (piezo) common rail system, piezoelectric actuators instead of the solenoid valve, so get a more accurate injection control. No return pipe, the structure is more simple. Pressure from 200 to 2000 bar elastic adjustment. The minimum injection rate can be controlled at 0.5mm3, reducing the smoke and NOX emissions.

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