No. 2 Handa Road, Mazhu Town, Yuyao City
No. 2 Handa Road, Mazhu Town, Yuyao City
The common rail system separates fuel pressure generation from fuel injection. If we compare single pump diesel injection technology to a revolution in diesel technology, then the common rail can be called rebellious because it deviates from traditional diesel systems and approximates sequential gasoline injection systems. The common rail system has opened up a new way to reduce diesel engine emissions and noise. Europe can be said to be a paradise for diesel cars, with diesel cars accounting for 39% in Germany. Diesel cars have a history of nearly 70 years, and in the past 10 years, diesel engines have made rapid progress. In 1997, Bosch and Mercedes Benz jointly developed the Common Rail Diesel Injection System. Today in Europe, many brands of cars are equipped with common rail diesel engines, such as Peugeot's HDI common rail diesel engine, Fiat's JTD engine, and Delphi's Multec DCR diesel common rail system
The common rail system is different from the previous camshaft driven diesel injection system. The common rail diesel injection system completely separates the generation of injection pressure and the injection process from each other. The electromagnetic valve controlled injector replaces the traditional mechanical injector, and 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, which continuously adjusts the pressure according to the operating needs of the engine. The pulse signal applied by the electronic control unit to the injector solenoid valve controls the fuel injection process. The fuel injection quantity depends on the oil pressure in the fuel rail, the duration of the solenoid valve opening, and the fluid flow characteristics of the fuel injector
Fuel injection pressure is an important indicator of diesel engines because it is related to the engine's power, fuel consumption, emissions, etc. The common rail diesel injection system has increased the fuel injection pressure to 1800 bar
In the past two years, cars equipped with direct injection diesel engines have seen significant development in Europe, with high efficiency, excellent fuel economy, and reduced engine noise. Direct injection diesel engines use a pump nozzle system, and the domestically produced 1.9TDI Bora uses this system, with a maximum injection pressure of 1800 bar. Although the pump nozzle direct injection system is good, the fuel pressure cannot be kept constant. With more stringent emission control, higher and constant diesel injection pressure and more complete electronic control are needed. Therefore, many manufacturers have taken the more advantageous diesel common rail system as 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. By controlling the above characteristics, the common rail has made the responsiveness and driving comfort of diesel engines reach the level of gasoline engines, while it has significant fuel economy and low emission characteristics. Ensure high fuel pressure within all engine speed ranges, and high injection pressure can achieve good combustion characteristics at low speeds. The engine with an axial piston distribution pump driven and controlled by a camshaft has a linear relationship between fuel system pressure and engine speed, resulting in insufficient fuel pressure at low engine speeds, while the common rail system can achieve very high fuel pressure across all engine speed ranges. The flexible electronic control system can achieve low emissions and high efficiency in controlling timing and injection pressure under various engine operating conditions. Due to the separation of pressure formation and injection process, engine designers have gained greater freedom in 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 even at low speeds, thus obtaining high torque even at very low speeds. The application of pre injection technology has made greater progress in reducing emissions and noise
2、 The fuel supply system is precisely controlled
The low-pressure fuel pump draws diesel from the tank, filters it, and provides it to the high-pressure fuel pump. There is an electromagnetic valve inside the low-pressure pump that controls the fuel to reach the high-pressure pump chamber, and the fuel enters the tubular accumulator fuel rail. There is a pressure sensor on the common rail that constantly monitors the fuel pressure and transmits this signal to the ECU. By adjusting the flow rate, the fuel pressure in the common rail is controlled to reach the desired value. The injection pressure varies from 200 to 1800 bar depending on the engine operating conditions, and is then controlled by a computer to be injected into each cylinder. The common rail not only maintains fuel pressure, but also eliminates pressure fluctuations
Fuel injection is a complex combination of mechanical, hydraulic, and electronic systems that must adapt to the working environment of the engine under various operating conditions. Before combustion, the fuel must be filtered and pressurized, and injected into each cylinder at a certain injection rate at an accurate time. The engine computer controls the exhaust gas recirculation, turbocharging, and exhaust aftertreatment systems to achieve optimal engine characteristics and exhaust emissions
3、 The smallest displacement common rail engine and the latest generation common rail engine
The compact structure of the fuel injector makes the common rail system a practical solution even for small displacement 4-valve engines. Smart, equipped with a 3-cylinder common rail diesel engine, was born at the end of 1999. Its displacement is only 799mL, with a maximum power of 30kW and a maximum torque output of 100Nm between 1800-2800rpm
The second-generation common rail engine is installed on the E320 launched by Mercedes Benz this year, with a maximum power of 150kW and an output torque of 250Nm at 1000rpm. 85% of the peak torque can be obtained at 1400rpm, and a peak torque of 500Nm can be achieved in the wide range of 1800-2600rpm. The acceleration time from 0 to 100km/h is only 7.7 seconds, and the maximum speed is 243km/h. The comprehensive fuel consumption is 6.9L/100km, and the 80L fuel tank enables a range of 1000km. The comprehensive fuel consumption of E320 equipped with gasoline engine is 9.9L/100km
4、 The diesel common rail system has been developed for three generations and has strong technological potential. The first generation common rail high-pressure pump always maintained the highest pressure, resulting in energy waste and high fuel temperature. The second generation can change the output pressure according to engine requirements 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 within one millionth of a second before the main injection, preheating the combustion chamber. The preheated cylinder makes compression ignition easier after main injection, and the pressure and temperature inside the cylinder no longer increase suddenly, which is beneficial for reducing combustion noise. During the expansion process, post injection is carried out to generate secondary combustion, increasing the cylinder temperature by 200-250 ℃ and reducing the hydrocarbons in the exhaust
Due to its powerful technological potential, today manufacturers have set their sights on the third generation of common rail systems - piezoelectric common rail systems, where piezoelectric actuators replace solenoid valves, resulting in more precise injection control. Without the oil return pipe, the structure is simpler. The pressure is adjusted elastically from 200 to 2000 bar. The minimum injection volume can be controlled at 0.5mm3, reducing smoke and NOX emissions
