Development of Fuel Injection System for Diesel Engine

1. Main development stages of diesel engine fuel injection system
Since Diesel engine was invented by Diesel in 1892, due to the limitation of technology at that time, no suitable fuel supply system has been found. There was no substantial progress in the next 30 years.In order to solve the problem of fuel supply, Bosch Company developed an in-line synthetic pump for diesel engines in the late 1920s. As a result, the technology of diesel engine is developing rapidly, and diesel engine is becoming more and more popular in people's production and life.However, after the 1970s, the oil crisis and the diesel engine emission pollution incident.The further development of diesel engine technology is facing both new development opportunities and new challenges [4-6].The development of diesel engine fuel injection system has gone through four stages:
(1) From 1892 to 1927, early diesel engines used an air injection system, in which 7 MPa of compressed air was used to blow fuel into the cylinder.
(2) From 1927 to 1970, the diesel engine adopted mechanical injection system, which was mainly composed of mechanical injection pump and injector.Due to the low control accuracy of mechanical speed governor and mechanical fuel injection advance, the response is not sensitive.Although these mechanical devices also realize the control of the main parameters that affect the economy and emission of diesel engines,However, the control effect is still not satisfactory.Therefore, the traditional mechanical control mechanism is difficult to meet the requirements of further improving the performance and reducing emissions of diesel engines.Even if it is further complicated, it is difficult or even impossible to realize high-precision control.
(3) From 1970 to 1995, the conventional electronic control fuel injection system appeared, which is characterized by high control accuracy and large control freedom.The control function is complete,The injection characteristics (injection pressure, injection quantity, injection timing and injection rate) of the fuel injection system can be changed with the working conditions of the diesel engineThe state optimization greatly reduces the harmful emissions of the diesel engine and improves its economy.

(4) Since 1995, a brand new fuel injection system, electronically controlled common rail fuel injection system, has been developed as shown in Figure 1.1. It is characterized in that the actual running state of the diesel engine can be detected by a sensor, After data processing, the injection time, injection rate and injection quantity are optimally controlled by corresponding actuators.Meanwhile, the pressure in the common rail pipe is controlled by adjusting the fuel quantity entering the common rail pipe.

Figure 1 Electronically Controlled Common Rail Fuel Injection System

2. Development of Electronically Controlled Fuel Injection System for Diesel Engine
Three generations of foreign diesel engine electronically controlled fuel injection systems have been introduced, as shown in Table 1.1.
Table 1 Development of Electronic Fuel Injection System of Foreign Diesel Engine

Figure 2 Development of Fuel Injection Pump

From the development of the 1970s to the practical use of the 1980s, the electronic fuel injection system based on position control belongs to the first generation of products.It only needs to replace the original mechanical plunger pump with an electric control pump and its control components to become an electric control system.The structure of the diesel engine hardly needs to be changed, so that the control precision and the response speed are improved, the production inheritance is good,However, the control flexibility and transient control effect are not ideal enough, and the injection pressure and injection rate can not be effectively controlled.The more mature products are: ① Improvement on the basis of distribution pump.For example, the EDCCOVEC system of Bosch Company in Germany and the ECD VI system of Denso Company in Japan. ② Implement position control on the in-line pump. Such as COPEC system and TICS system of Zexel Company in Japan.

Features of these products:
① Or the position of the rack or the sliding sleeve is controlled by a proportional electromagnet or a direct current motor, and a position sensor is used as a feedback signal, Realizing the control of the fuel injection quantity;
② Or the original fuel injection advancer is improved, and an electro-hydraulic servo mechanism is adopted to control the position of a piston of the fuel injector, Realize the control of fuel injection timing.

In the 1990s, The second generation of electronic control injection system with time control and the third generation of electronic control injection system with pressure and time control appeared one after another. The time-controlled injection system changes some mechanical structures of the conventional injection system, The characteristic that the plunger pump can bear high pressure is utilized to provide high oil supply pressure, The oil injection start point and oil injection quantity are directly controlled by using a high-speed and powerful electromagnetic overflow valve, which has the advantages of direct control and quick response. It can reach very high injection pressure, but it can not realize flexible adjustment of injection pressure and flexible control of injection rate.

Typical time-controlled injection systems include the Model 1 distribution pump system of Zexel Company in Japan and the ECD of Denso Company in JapanV3 distribution pump system, DS and RS distribution pump system of Stanadyne Company in the United States, DDEC system of Detroit Company in the United States and EU of Lucas Company in the United KingdomI system, etc.

Compared with the position control system and the time control system,The pressure-time control type electronic control injection system completely gets rid of the original system structure of an injection pump,The computer control technology, the modern sensing detection technology and the high speed solenoid valve technology are integrated into the advanced fuel injection mechanismA brand new electronically controlled injection system,The start and stop of the injection of the fuel injector can be controlled by the solenoid valve: the injection timing is determined by the action time of the solenoid valve,The amount of fuel injection is determined by the duration of action and the common rail pressure. It is different from the traditional plunger pump which adopts the principle of separate cylinder pulsation oil supply.The new electronically controlled injection system adopts the pressure-time fuel metering principle.The oil injection control is realized by combining the continuous control of the oil pressure of the common oil duct and the electromagnetic valve control of the injection process of each cylinder,Therefore, it is called pressure-time control electronic control injection system, also known as electronic control common rail injection system.The system can not only control the fuel injection quantity and the fuel injection timing in time,But also can control the injection pressure and the injection rate which can not be controlled in the past,The degree of freedom and control precision of the system have been greatly improved.Common rail injection system can be divided into medium pressure common rail injection system and high pressure common rail injection system.The basic principle of fuel injection control of the two systems is the same, but the structure of the fuel injector is different.Pressure amplification is added in the injector of medium pressure common rail injection system, and the structure is complex.Typical examples are HEUI system developed by Caterpillar Company in the United States and Servojet system developed by BKM Company in the United States.In the case of high-pressure common rail injection systems,Nippondenso has developed the ECDU2 high pressure common rail injection system (shown in Figure 1.2) for medium duty diesel engines.After successfully matching with Hino J08C diesel engine, it was successfully matched with Isuzu HK series diesel engine. By 2001, the monthly/output will reach more than 2000 sets;In 1997, the world's first Unijet high-pressure common rail injection system was successfully developed by Fiat Group in Italy.And was tried out on the Alfa 156. In 2003, Fiat successfully developed the second generation JTD 16-valve multiple injection diesel engine;The first generation of high pressure common rail injection system developed by Bosch Company in Germany was put on the market in July 1997.The second generation started mass production in 2000, and the third generation of high pressure common rail fuel injection system has been able to strictly meet the Euro IV emission standards.

At present, Bosch, Germany, is directly applying the technology of coaxial variable nozzle and pressure amplifier to the development of high-pressure common rail injection system. It is believed that the high-pressure common rail injection system with a maximum injection pressure of more than 200 MPa will become a practical product in the near future. In addition, the CR system developed by Bosch on the basis of Fiat's Unijet system is mainly used in cars. After successfully matching with the products of BENZ, VW, BMW and other companies, the annual output of CR system is more than 1 million units. And developed a series of products from low power to medium power. In addition, Lucas Company in the United Kingdom and Stanadyne Company in the United States have also developed their own high-pressure common rail electronically controlled injection systems.