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From January 1, 2007, China's new car with compression ignition engine adopts the National III emission standard (GB17691-2005). From July 1, 2008 onwards, Beijing has implemented the national IV emission standards for buses and sanitation that are sold and registered in Beijing, and heavy duty compression-ignition engines for postal service, and it is required to install OBD (on-board diagnostic system).
Major differences between the national III, national IV and national II emission standards
In addition to reducing pollutant emissions, the National III compression-ignition engine also modifies the National II test cycle and specifies tests such as the ESC (EuropeansteadystateCycle), the European LoadResponseTest (ELR), and the European TransientCycleTest (ETC). program. Including the installation of fuel injection system, exhaust gas recirculation (EGR) and oxidation catalytic converter National III diesel engine, should use ESC and ELR test procedures to determine the emission of pollutants. For diesel engines equipped with NOx catalytic converters and particulate traps, transient cycle ETC test procedures shall be added to determine exhaust pollutants. All IV, V diesel engines are required to perform all ESC, ELR, and ETC tests. Starting from the national IV stage, the new model should be equipped with an on-board diagnostic system (OBD) or an on-board measurement system (OBM) to monitor the discharge of pollutants during use. From the national phase IV stage, the durability requirements of emission control devices and the in-use vehicle compliance requirements have been increased. The increase of OBD is the core of implementation of State IV emission standards. This system will monitor the exhaust gas at any time based on the engine operating conditions. When the system fails, the fault light or check engine warning light is on. The OBD should ensure that it can identify whether the vehicle emissions are excessive during the service life of the vehicle.
Electronically controlled high pressure fuel injection system
The electronically controlled high pressure fuel injection system currently has three types of single pump, pump nozzle, and common rail. Monomer pump and common rail are widely used in commercial vehicle diesel engines in China.
An ideal fuel injection system should have the following properties: high injection pressure (above 1000 bar), and the injection pressure can be flexibly adjusted according to working conditions, and the oil injection timing, fuel injection quantity and fuel injection rate can be precisely controlled.
1. Electronically controlled monomer pump
The single pump system is a high pressure fuel injection system with time control for direct injection diesel engines. They have a transient injection pressure of up to 2050 bar, a variable injection starting point and can be pre-injected. The system consists of the low-pressure and high-pressure parts of the fuel supply system, electronic control units and sensors. The unit pump is operated by a high pressure diesel injection system made of an integral solenoid valve. The moment when the solenoid valve is triggered is the moment when it is closed and the starting point of the fuel supply is determined. The length of solenoid valve triggering determines the size of the fuel injection. The electronic unit pump is mounted on the outside of each cylinder directly from the injection cam on the engine camshaft. The high-pressure fuel is pumped into the injector by the unit pump through the high-pressure tubing and the high-pressure short tube, and then injected into the combustion chamber of the cylinder. Because of this arrangement, the structure of the cylinder head does not change much and is therefore very popular with commercial vehicle and diesel engine manufacturers. Abroad, such as Mercedes-Benz, Deutz, Caterpillar, Duff, etc. are using monomer pumps. China's commercial diesel engine companies such as Dachai, Yuchai, Weichai also use monomer pumps to meet the national III emission standards.
2. Electronically controlled high pressure common rail fuel injection system
The electronically controlled high pressure common rail fuel injection system is a new concept fuel injection system based on direct injection technology, pre-injection technology and electronic control technology. It consists of a high pressure pump, a common rail with a pressure sensor and a pressure regulator, a solenoid valve or piezoelectric injector, an electronic control unit (ECU) and sensors.
The advantages of the common rail fuel injection system are:
1 can achieve high-pressure injection, up to 2000bar;
2 The injection pressure is independent of the engine speed, which can improve the engine's low speed load characteristics;
3 can achieve pre-injection and post-injection, adjust the shape of the injection rate, to achieve the ideal fuel injection law;
4 fuel injection timing and fuel injection can be freely selected;
5 has a good injection characteristics, optimize the combustion process, so that the engine fuel consumption, smoke, noise and emissions and other comprehensive performance indicators have been significantly improved, is conducive to improving the engine torque characteristics;
6 It has a simple structure, good reliability, and strong practicality. It has been widely used in commercial vehicle diesel engines in various countries. The electronically controlled high pressure common rail fuel injection system has been developed to the fourth generation. The first generation is a solenoid valve injector with a fuel injection pressure of 1350 bar; the second generation is a solenoid valve injector with an injection pressure of 1600 bar; the third generation is a pressure with an injection pressure of 1600 to 2000 bar. Electric injectors. Its main feature is that the quartz piezoelectric actuator replaces the high-speed solenoid valve to open the injector needle valve. Bosch's quartz piezoelectric injectors use quartz crystals to expand under the action of an electric field, allowing injectors to respond within 1/10000s. They respond twice as fast as high-speed solenoid valves and are very small in size. , and there is no friction. As a result, a more accurate injection quantity can be achieved, and the atomization quality of the fuel injection can be improved, and the time interval between the pre-injection, the main injection, and the after-injection can be further shortened to achieve more flexible control over the entire injection process. Siemens was the first to develop piezoelectric injectors.
The fourth generation is a hydraulic supercharged injector with an injection pressure of up to 2500 bar, which allows a very high injection pressure at the injector needle valve, further improving the fuel atomization quality, and at the same time making Rails and common rails maintain relatively low oil pressure in the high pressure tubing leading to injectors (common rail pressure is only 1350 bar). When Bosch developed the fourth-generation common-rail fuel injection system, in addition to the increase of injection pressure, it also provided a new injection law to reduce the generation of NOx during combustion, allowing the injection pressure to gradually increase, thus achieving a smooth cylinder Combustion maintains a slow temperature gradient and low NOx production, which in turn improves the formation of gas mixtures and helps to reduce the formation of PM particles.
Classification of Electronically Controlled High Pressure Common Rail Fuel Injection System
The electronically controlled high pressure common rail fuel injection system has three types: common rail hydraulic, high pressure common rail, and common rail supercharged.
Common rail hydraulic fuel injection system
Caterpillar's HEUI system is an electronically controlled medium pressure common rail hydraulic fuel injection system.
Electronically controlled medium pressure common rail hydraulic fuel injection system consists of high pressure oil pump, common rail oil pressure control valve, injector with solenoid valve, sensor, electronic control unit, fuel oil pump and other components. The system divides the two oil and oil lines. The engine oil is the control oil of the injector. The high pressure oil pump conveys the oil to the high pressure common rail. The oil pipeline is composed of two parts, low pressure and high pressure. The pressure of the low-pressure tubing is 3bar, and its function is to send the oil to the high-pressure oil pump by the oil pump through the oil cooler and the oil filter. The high pressure oil pump will send the oil to the high pressure common rail tube, the pressure is controlled at 40230bar, and the pressure control valve of the common rail oil tube is controlled by the electronic control unit to regulate the pressure. The specific value is adjusted according to the engine performance needs.
The system features are:
1 The use of oil as the control oil solves the problems of viscosity reduction and hot start of diesel fuel under hot conditions.
2 Because the oil viscosity is higher than that of diesel oil, the system is easy to seal.
3 Control oil is provided with oil return pipeline. After the control is completed, the oil returns to the cylinder head as lubricating oil.
4 For each fuel injection process, the solenoid valve must complete one switch and the solenoid valve has a high response time.
5 Compared with the traditional fuel injection pump, it is easy to manufacture.
6 Cold start is more difficult.
2. Common rail fuel injection system
This high pressure common rail fuel injection system is currently widely used. Bosch, Denso, Siemens VDO (now Continental Automotive Systems), Delphi, and Marelli are all producing.
At present, the solenoid valve of the injector of the high pressure common rail fuel injection system has been developed toward the piezoelectric type. With the increase of the pressure of the common rail, there are strict requirements on the material and processing precision of the common rail. Bosch's piezoelectric injector with the maximum common rail pressure of 2000 bar will also be put into production. However, it is difficult to further improve the pressure of the common rail. Therefore, a common rail fuel injection system for hydraulic booster injectors is being developed.
3. Hydraulic booster common rail fuel injection system
The supercharged common-rail fuel injection system adopts a booster piston, which increases the injection pressure by means of supercharging. The medium-pressure fuel in the common-rail tube pushes the booster piston to provide high-pressure oil to the injector. Solenoid valve control Hydraulic booster injectors are the most important components in the system. When the solenoid valve is closed, the fuel in the common rail enters above the booster piston and the piston descends. Since the ratio of the booster piston diameter to the plunger diameter is 1:15, the pressure of the fuel in the booster piston, the injector needle valve chamber and the top of the needle valve can reach 1000-1500 bar when the piston descends. When the solenoid valve is opened, the pressure above the booster piston is relieved, and the piston goes upward, the oil pressure at the top of the injector needle valve drops, and the high pressure oil in the plenum lifts the needle valve to achieve high pressure injection. At present, the hydraulic booster common rail fuel injection system has an injection pressure of up to 2500 bar, and the common rail pressure is relatively low, only 1350 bar, much smaller than the third generation of the common rail fuel injection system (common rail pressure is 1600~ 2000 bar) fuel pressure, relatively low requirements for common rails and seals. This is the direction of high-pressure fuel injection systems for commercial vehicle diesel engines, which can improve the quality of fuel atomization and reduce fuel consumption and engine emissions.