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High-pressure common rail

High-pressure common rail

2019-12-18 14:51
High-pressure common rail (Common Rail) EFI technology refers to a fuel supply method that completely separates the generation of injection pressure and the injection process from each other 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 fuel pump to deliver high-pressure fuel to the public fuel supply pipe (Rail). The oil pressure in the public fuel supply pipe is used to achieve precise control, making the pressure of the high-pressure fuel pipe independent of the engine speed, which can greatly reduce the diesel The degree to which the fuel supply pressure varies with engine speed.
Common rail technology refers to a fuel supply method that completely separates the generation of injection pressure and the injection process from a closed-loop system composed of a high-pressure oil pump, a pressure sensor, and an ECU. The precise control of the oil pressure in the public fuel supply pipe makes the pressure of the high-pressure fuel pipe independent of the engine speed, which can greatly reduce the change in the fuel supply pressure of the diesel engine with the engine speed, thus reducing the defects of the traditional diesel engine. The ECU controls the fuel injection quantity of the fuel injector. The fuel injection quantity depends on the pressure of the fuel rail (common fuel supply pipe) and the length of the solenoid valve opening time.
High pressure common rail is a kind of diesel fuel injection
The common rail system separates fuel pressure generation from fuel injection. If the single-pump diesel injection technology is compared to the revolution in diesel technology, the common rail system can be called a rebel because it deviates from the traditional diesel system and approximates it. For sequential gasoline injection systems. Common rail system opens up new ways to reduce diesel engine emissions and noise
Europe can be said to be a paradise for diesel cars, accounting for 39% of German diesel cars. Diesel cars have a history of nearly 70 years, and in the last 10 years, it can be said that diesel engines have made rapid progress. In 1997, Bosch and Mercedes-Benz jointly developed the Common Rail Diesel Injection System (Common Rail System). Today in Europe, many brands of cars are equipped with common rail diesel engines. For example, Peugeot has HDI common rail diesel engines, Fiat's JTD engine, and Delphi has developed the Multec DCR diesel common rail system.
The common rail system is different from the previous diesel injection system driven by the camshaft. The common rail diesel injection system completely separates the generation of injection pressure and the injection process from each other. The solenoid valve controlled injector replaces the traditional mechanical injector. The fuel pressure in the fuel rail is generated by a radial plunger high pressure pump. The pressure is independent of the engine speed and can be freely set within a certain range. . The fuel pressure in the common rail is controlled by an electromagnetic pressure regulating valve, and continuous pressure regulation is performed according to the working needs of the engine. The pulse signal on the solenoid valve of the electronic control unit controls the fuel injection process. The amount of fuel injection depends on the oil pressure in the fuel rail, the length of time the solenoid valve is open, and the liquid flow characteristics of the injector.
Fuel injection pressure is an important indicator for diesel engines, because it is related to the engine's power, fuel consumption, and emissions. Common rail diesel injection system has increased fuel injection pressure to 1800 bar
In the past two years, cars with direct-injection diesel engines have developed significantly in Europe, with high efficiency and excellent fuel economy, and reduced engine noise. The direct injection diesel engine uses a pump nozzle system. The domestically produced 1.9TDI Bora applies this system, and the maximum injection pressure can reach 1800 bar. Although the pump nozzle direct injection system is good, the fuel pressure cannot be kept constant. As the emission control becomes more stringent, higher and constant diesel injection pressure and better electronic control are required. Therefore, many manufacturers have made the advantages more Many diesel common rail systems are the development direction of diesel engines. This system has high fuel pressure and can provide flexible fuel distribution control. The ECU flexibly controls fuel distribution, fuel injection time, injection pressure and injection rate. Through the control of the above characteristics, the common rail has made the diesel engine's responsiveness and driving comfort reach the level of gasoline engines, and at the same time it has significant fuel economy and low emission characteristics.
保证 Ensure high fuel pressure in all speed ranges of the engine, high injection pressure can get good combustion characteristics at low speed conditions
The engine of the axial plunger-type distribution pump controlled by the camshaft drive has a linear relationship between the fuel system pressure and the engine speed, resulting in insufficient fuel pressure at low engine speeds, and the common rail system can achieve very High fuel pressure. The flexible electronic control system controls timing and injection pressure to achieve low emissions and high efficiency under various engine operating conditions. The separation of pressure from the injection process gives engine designers greater freedom when studying combustion and injection processes. The injection pressure and injection timing can be adjusted according to the requirements of the engine operating conditions, so that the engine can achieve complete combustion at low speeds, so it can obtain large torque even at very low speeds. The application of pre-injection technology has made greater progress in reducing emissions and noise.
油 Oil supply system is precisely controlled
The low-pressure oil pump sucks the diesel from the fuel tank and supplies it to the high-pressure oil pump after filtering. There is a solenoid valve in the low-pressure pump to control the fuel to reach the high-pressure pump chamber, and the fuel enters the tube-shaped accumulator-fuel rail. There is a pressure sensor on the common rail to constantly monitor the fuel pressure, and this signal is transmitted to the ECU, and the fuel pressure in the common rail is controlled to achieve the desired value by adjusting the flow rate. The injection pressure varies from 200 to 1800 bar depending on the operating conditions of the engine, and is injected into the cylinders separately through computer control. The common rail not only maintains the fuel pressure, but also eliminates pressure fluctuations.
Fuel injection is a complex combination of mechanical, hydraulic, and electronic systems. To adapt to the working environment of the engine under various operating conditions, the fuel must be filtered and pressurized before combustion, and injected at a certain injection rate at an accurate time. Inside each cylinder. The engine computer controls exhaust gas recirculation, boost, and exhaust aftertreatment systems to obtain the best engine characteristics and exhaust emissions.
Minimum displacement common rail engine and latest generation common rail engine
The compact structure of the injector makes the common rail system a practical solution even for small-displacement 4-valve engines. At the end of 1999, a Smart equipped with a three-cylinder common rail diesel engine was born. Its displacement is only 799 mL, the maximum power is 30 kW, and the maximum torque is 100 Nm at 1800-2800 rpm.
The second-generation common-rail engine was installed on the E320 launched by Mercedes-Benz this year, with a maximum power of 150kW and an output torque of 250Nm at 1000rpm. At 1400rpm, 85% of the peak torque can be obtained. In the wide area of ​​1800-2600rpm, 500Nm Peak torque. The acceleration time from 0 to 100 km / h is only 7.7 seconds, and the maximum speed is 243 km / h. The comprehensive fuel consumption is 6.9L / 100km, and the 80L fuel tank enables the endurance to reach 1000km. The E320 equipped with a gasoline engine has a combined fuel consumption of 9.9L / 100km.
Diesel common rail system has been developed for 3 generations, it has strong technical potential
The first generation of common rail high pressure pumps were always maintained at the highest pressure, resulting in wasted energy and high fuel temperatures. The second generation can change the output pressure according to the engine demand, and has pre-injection and post-injection functions. Pre-injection reduces engine noise: a small amount of fuel is injected into the cylinder for compression ignition, and the combustion chamber is pre-heated within one millionth of a second before the main injection. The preheated cylinder makes the compression ignition easier after the main injection, and the pressure and temperature in the cylinder no longer increase suddenly, which is beneficial to reducing the combustion noise. Post-injection during the expansion process produces secondary combustion, which increases the temperature in the cylinder by 200-250 ° C, reducing the hydrocarbons in the exhaust.
Due to its strong technical potential, today all manufacturers have set their sights on the third generation of the common rail system-the piezo common rail system. Piezo actuators have replaced the solenoid valves, so they have been more accurate. Jet control. Without the oil return pipe, the structure is simpler. The pressure is elastically adjusted from 200 to 2000 bar. The minimum injection volume can be controlled at 0.5mm3, which reduces the smoke and NOX emissions.
"Electrical control" means that the fuel injection system is controlled by a computer. The ECU (commonly known as a computer) precisely controls the fuel injection amount and timing of each fuel injection nozzle, which can make the fuel economy and power of the diesel engine reach the best. Balance, while the traditional diesel engine is controlled by machinery, the control accuracy cannot be guaranteed.
"High pressure" means that the pressure of the fuel injection system is three times higher than that of traditional diesel engines, and the maximum pressure can reach 200 MPa (while the fuel injection pressure of traditional diesel engines is 60-70 MPa). The pressure is high and the atomization is good and the combustion is sufficient, thereby improving the power performance. Finally, the goal of saving fuel is achieved.
The "common rail" is to supply each injector simultaneously through a common fuel supply pipe. The fuel injection quantity is accurately calculated by the ECU, and at the same time, the fuel of the same quality and pressure is provided to each injector to make the engine run more smoothly, thereby optimizing the diesel engine. Comprehensive performance. Traditional diesel engines inject fuel from each cylinder, the injection volume and pressure are inconsistent, and the operation is uneven, resulting in unstable combustion, high noise and high fuel consumption.
Now, domestically manufactured diesel engines with internationally advanced electronically controlled high-pressure common rail technology use the latest core technologies of European and American diesel engines, which are significantly better than traditional supercharged diesel engines. It has 8% higher combustion efficiency, 10% lower carbon dioxide emissions, and 15% lower noise than traditional turbocharged diesel engines, completely changing the image of diesel engines as "noisy and smoky" in people's minds.

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