Talking about High Pressure Common Rail Electronic Spray Technology

Common Rail EFI technology refers to a fuel supply system in which the injection pressure generation and injection process are completely separated 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 is a high-pressure oil pump that delivers high-pressure fuel to a common rail (Rail). The oil pressure in the public supply pipe can be precisely controlled so that the pressure of the high-pressure pipe is independent of the engine speed, which can greatly reduce the diesel engine's pressure. Supply pressure changes with engine speed.

Common-rail technology refers to a type of oil supply system in which a high-pressure oil pump, a pressure sensor, and an ECU comprise a closed-loop system consisting of a spray pressure and a spray process that are completely separated from each other. The high-pressure fuel pump conveys the high-pressure fuel to the public oil supply pipe. The accurate control of the oil pressure in the public oil supply pipe makes the pressure of the high pressure oil pipe irrelevant to the engine speed, which can greatly reduce the variation of the fuel supply pressure of the diesel engine with the engine speed, thus reducing the defects of the conventional diesel engine. The ECU controls the injection quantity of the injector. The injection quantity depends on the pressure of the fuel rail (public supply pipe) and the length of the solenoid valve opening time.

The common rail system separates the fuel pressure generation from the fuel injection. If the single pump diesel injection technology is likened to the revolution of diesel technology, the common rail can be called rebellion because it deviates from the traditional diesel system and is similar to it. In order gasoline injection system. Common rail systems open up new ways to reduce diesel engine emissions and noise.

Europe can be said to be a paradise for diesel cars, with German diesel cars accounting for 39%. Diesel cars have a history of nearly 70 years. In the last 10 years, diesel engines have seen rapid development. In 1997, Bosch and Mercedes-Benz jointly developed the Common Rail System. In Europe today, many brands of cars are equipped with common-rail diesel engines. For example, Peugeot has HDI common-rail diesel engines and Fiat's JTD engines, while Delphi has developed the Multec DCR diesel common-rail system.

Difference between common rail system and diesel injection system

The common rail system differs from the diesel injection system previously driven by a camshaft. The common rail diesel injection system completely separates the injection pressure generation 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 piston 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 adjustment is performed according to the working requirements of the engine. The electronic control unit acts on the pulse signal on the solenoid valve of the injector to control the fuel injection process. The amount of fuel injection depends on the oil pressure in the fuel rail and the length of the solenoid valve opening time, and the liquid flow characteristics of the injector.

Fuel injection pressure is an important indicator for diesel engines because it is linked to engine power, fuel consumption, and emissions. Common rail diesel injection system has increased fuel injection pressure to 1800 bar

Development in recent years

In the last two years, cars that match direct-injection diesel engines have grown significantly in Europe, have high efficiency and excellent fuel economy, and have reduced engine noise. The direct injection diesel engine uses a pump nozzle system. The domestically produced 1.9TDI Polaris applies this system with a maximum injection pressure of up to 1800 bar. Although the direct injection system of the pump nozzle is good, the fuel pressure cannot be kept constant. As the emission control is more demanding, higher and constant diesel injection pressures and better electronic control are needed, so many manufacturers take advantage of it. 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 can flexibly control the 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 the gasoline engine, while it has significant fuel economy and low emission characteristics. High fuel pressure is ensured in all engine speed ranges. High injection pressure can achieve good combustion characteristics under low-speed operating conditions. Engine of axial piston type distribution pump driven by camshaft. Fuel system pressure and engine speed In a linear relationship, fuel pressure is insufficient at low engine speeds, and the common rail system can achieve very high fuel pressures over all engine speed ranges. The flexible electronic control system controls the timing and injection pressure to achieve low emissions and high efficiency in all engine operating conditions. Because the formation of pressure is separated from the injection process, engine designers gain greater freedom in studying the 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 under low speed conditions, so even at a low speed, large torque can be obtained. The application of pre-injection technology has made greater progress in reducing emissions and noise.

Accurate control of oil supply system

The low-pressure oil pump sucks the diesel oil out of the oil tank and supplies it to the high-pressure oil pump after filtration. There is a solenoid valve in the low-pressure pump to control the fuel oil to reach the high-pressure pump chamber, and the fuel enters the tubular pressure accumulator-fuel rail. A pressure sensor on the common rail constantly monitors the fuel pressure and passes this signal to the ECU. By adjusting the flow rate, the fuel pressure in the common rail reaches the desired value. The injection pressure varies from 200 to 1800 bar depending on the operating conditions of the engine, and is then injected into the cylinder 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 conditions, the fuel must be filtered and pressurized before it is burned. It is injected at a precise injection rate at an accurate time. Every cylinder. The engine computer controls the exhaust gas recirculation, booster, and exhaust after-treatment systems for optimal engine characteristics and exhaust emissions.

Latest Generation Common Rail Engine

The compact structure of the injector allows the common rail system to be a practical solution even for small displacement 4-valve engines. At the end of 1999, Smart was equipped with a three-cylinder common-rail diesel engine. Its displacement was only 799 mL, and its maximum power was 30 kW. Its maximum torque was 100 Nm at 1800-2800 rpm.

This year, Mercedes-Benz launched the E320 with a second-generation common-rail engine with a maximum output of 150 kW and an output torque of 250 Nm at 1000 rpm. At 1400 rpm, 85% of the peak torque can be achieved, and 500 Nm can be achieved over a wide range of 1800 to 2600 rpm. Peak torque. 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 has a life of 1000km. The combined fuel consumption of the E320 with a gasoline engine is 9.9L/100km.

Three generation diesel common rail system

The diesel common rail system has been developed for three generations. It has strong technological potential. The first-generation common-rail high-pressure pumps always maintain the highest pressure, resulting in wasted energy and high fuel temperatures. The second generation can change the output pressure according to engine demand and has pre-injection and post-injection functions. Pre-injection reduces engine noise: A small fraction of a millionth of a second before the main injection is injected into the cylinder to ignite, preheating the combustion chamber. The preheated cylinder makes the compression after the main injection easier, the pressure and temperature inside the cylinder no longer increase abruptly, and it is beneficial to reduce the combustion noise. Post-injection during the expansion process produces secondary combustion, increasing the in-cylinder temperature by 200-250°C, reducing the hydrocarbons in the exhaust.

Due to its strong technical potential, manufacturers have now set their sights on the 3rd generation of common rail systems - piezo common rail systems. Piezo actuators have replaced solenoid valves and have been more accurate. Jet control. Without a 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, reducing 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 quantity and injection timing of each injector, and can achieve the best fuel economy and power of the diesel engine. Balanced, while the traditional diesel engine is controlled by the machine, the control accuracy can not be guaranteed. “High pressure” means that the fuel injection system pressure is 3 times higher than that of a conventional diesel engine, and the highest energy can reach 200 MPa (and the traditional diesel fuel injection pressure is 60-70 MPa), and the pressure is large enough for atomization to burn well, thereby improving dynamic performance. Ultimately achieve the purpose of fuel-efficient.

The “common rail” is supplied by the common oil supply pipe at the same time to each fuel injector. The fuel injection quantity is accurately calculated by the ECU. At the same time, fuel of the same quality and the same pressure is supplied to each injector to make the engine run more smoothly, thereby optimizing the diesel engine. Comprehensive performance. The traditional diesel engine is fuel injected by each cylinder, the fuel injection volume and pressure are inconsistent, and the operation is uneven, resulting in unstable combustion, high noise, and high fuel consumption.

Nowadays, domestically-manufactured diesel engines with advanced electronically controlled high-pressure common rail technology have adopted the latest core technologies of diesel engines from Europe and the United States, which are clearly superior to conventional supercharged diesel engines. Compared with the traditional supercharged diesel engine, the combustion efficiency is increased by 8%, the carbon dioxide emission is reduced by 10%, and the noise is reduced by 15%. This completely changes the image of diesel engines in people's minds of “noise and black smoke”.

Structure principle

The high pressure common rail system uses a large-capacity common-rail chamber to accumulate high-pressure fuel from the pump, eliminate pressure fluctuations in the fuel, and then deliver it to each injector. Injection is achieved by controlling the solenoid valve on the injector. The beginning and termination.

Features

Its main features can be summarized as follows:

The high pressure in the common-rail chamber is used directly for injection, which eliminates the need for a booster in the injector. Also, the common-rail chamber has a continuous high pressure, and the required driving torque for the high-pressure pump is much smaller than the conventional oil pump.

By adjusting the pressure of the solenoid valve on the high pressure oil pump, the oil pressure in the common rail cavity can be flexibly adjusted according to the engine load conditions as well as the economical and emission requirements, and in particular, the low speed performance of the engine is optimized.

The solenoid valve on the injector controls the injection timing, the amount of fuel injected, and the injection rate, and also can flexibly adjust the amount of fuel injected by the pre-injection and the post-injection under different conditions and the interval between the injection and the main injection.

The high pressure common rail system consists of five parts: high pressure oil pumps, common rail cavities and high pressure fuel lines, fuel injectors, electronic control units, and various types of sensors and actuators. The fuel supply pump pumps fuel from the fuel tank into the oil inlet of the high-pressure pump. The engine-driven high-pressure oil pump pressurizes the fuel and feeds it into the common rail cavity. The solenoid valve controls each cylinder injector to inject fuel at the relevant time.

Pre-injection Before the main injection, a small portion of fuel is injected into the cylinder, pre-mixing or partial combustion takes place in the cylinder, shortening the ignition delay of the main injection. As a result, the pressure rise rate and peak pressure in the cylinder both decrease, the engine operation is relatively gentle, and the reduction in the temperature in the cylinder causes a reduction in NOx emissions. Pre-injection can also reduce the possibility of misfire and improve the cold start performance of high pressure common rail systems.

Lowering the injection rate early in the main injection can also reduce the amount of oil injected into the cylinder during the ignition delay period. Increasing the injection rate in the mid-term of the main injection can shorten the injection time and shorten the lean burn period, so that the combustion can be completed within a more effective crank angle range of the engine, increase the output power, reduce the fuel consumption, and reduce the soot emissions. Rapid fuel cut at the end of the main injection can reduce incomplete combustion of fuel, reduce smoke and hydrocarbon emissions.

maintenance

1, high pressure common rail system to ensure high-pressure injection, precise flow control, the accuracy of its components are very high, the coupling gap control is quite strict, part of the straightness at 0.8 microns, the couple gap between 1.5-3.7 microns , so it puts high demands on diesel cleanliness. The traditional diesel filter can only filter particles above 10 microns, and the 3 micron particle filtration efficiency is poor. The common rail system requires the filter to provide 95% water separation efficiency and 98.6% 3-5 micron particle filtration efficiency. At present, diesel fuel filters that meet this performance requirement are monopolized by foreign companies. Most of the OEM's products are imported products of foreign companies or foreign-funded enterprises produce in domestic investment factories. At present, there are also national brands that have entered the host facilities, such as Suzhou Industrial Park. Daphite. The quality of these companies' products is reliable. The main ones are: Foreign-funded enterprises: MH, Parker, Fleetguard, BOSCH, etc. Domestic brands are like DIFITE. 2. Current high pressure common rail system components are expensive. If the filter is replaced regularly according to the instructions, the injector will be damaged and the high pressure pump will be damaged. The maintenance cost is very expensive. Taking the current fuel consumption of a heavy truck as an example, it will probably cost more than 1,500 yuan.