Explanation of Diesel Engine Electronic Control Technology

Abstract

The development status, control principle and application characteristics of diesel engine electronic control technology, as well as the working principle, research direction and application prospects of high-pressure common rail technology are introduced.

Key words

The application prospects of diesel engine electronic control technology and high-pressure common rail technology

The development status and trend of electronic control technology for diesel engines

1.1 Development Status of Electronic Control Technology for Diesel Engines

Diesel engine electronic control technology originated in the 1970s. Since the 1980s, companies such as Lucas of the UK, Bosch of Germany, Mercedes-Benz, Detroit Diesel Engine Company of General Motors of the US, Cummins, Caterpillar, Isuzu Motors of Japan and Komatsu have all been competing to develop new products and put them on the market To meet the increasingly strict emission regulations.

Due to the characteristics of diesel engines such as high torque, long service life, low fuel consumption and low emissions, diesel engines have become the most realistic and reliable means to solve the energy problems of automobiles and construction machinery. Therefore, the application scope of diesel engines is getting wider and wider, and their quantity is increasing. At the same time, the requirements for the power performance, economic performance, control of exhaust emissions and noise pollution of diesel engines are also getting higher and higher. Relying on the traditional mechanical control fuel injection system can no longer meet the above requirements, and it is also difficult to achieve the requirement that the fuel injection volume, fuel injection pressure and injection timing operate completely in accordance with the optimal working conditions. In recent years, with the rapid development of computer technology, sensor technology and information technology, the reliability, cost, volume and other aspects of electronic products can all meet the requirements of electronic control of diesel engines, and electronic control of fuel injection is very easy to achieve.

In fact, the amount of CO and HC in the exhaust of diesel engines is much less than that of gasoline engines, and the NOX emissions are similar to those of gasoline engines, but there are more fine particles in the exhaust. This is related to the combustion mechanism of diesel engines. Diesel engines are a type of heterogeneous combustion. The formation time of the combustible mixture is very short, and the formation of the combustible mixture is intertwined with the combustion process. By analyzing the fuel injection rules of diesel engines, it is found that the atomization quality of the injected fuel, the flow of gas in the cylinder, and the shape of the combustion chamber all directly affect the progress of the combustion process and the generation of harmful emissions. Increasing fuel injection pressure and diesel atomization effect, as well as using pre-injection and staged injection, can effectively improve emissions.

After years of research and the application of new technologies, the current situation of diesel engines has changed significantly from the past. Modern advanced diesel engines generally adopt technologies such as electronic control injection, high-pressure common rail, and turbocharging intercooling. They have made significant breakthroughs in terms of weight, noise, and smoke intensity, reaching the level of gasoline engines. With the promulgation and implementation of increasingly strict international emission control standards (such as European IV and V standards), both gasoline engines and diesel engines are facing severe challenges. One solution is to adopt the technology of electronically controlled fuel injection. At present, the application rate of diesel engine electronic control technology in developed countries has reached over 60%.

1.2 What is an electronic fuel injection diesel engine

A diesel engine that uses electronic control for fuel injection and emissions is called an electronic fuel injection diesel engine. The electronic fuel injection diesel injection system consists of three parts: sensors, ECU(computer), and actuators. Its task is to electronically control the fuel injection system, achieving real-time control of the fuel injection volume and timing in accordance with the operating conditions. Sensors such as rotational speed, throttle pedal position, fuel injection timing, intake air temperature, intake air pressure, fuel temperature, and cooling water temperature are used to simultaneously input the real-time detected parameters into the computer (ECU) for comparison with the stored set parameter values or parameter maps (MAP). After processing and calculation, the instructions are sent to the actuator according to the optimal value or the calculated target value. The actuator controls the fuel injection volume (the position of the fuel supply rack or the duration of the solenoid valve closing) and the fuel injection timing (the opening and closing point of the timing control valve or the starting point of the solenoid valve closing) according to the instructions of the ECU, and at the same time controls the exhaust gas recirculation valve, preheating plug and other actuator mechanisms to ensure that the diesel engine operates at the best state.

1.3 Development Trends of Electronic Control Technology for Diesel Engines

1.3.1 High injection pressure

To meet the requirements of emission regulations, the diesel injection pressure has been raised from 10MPa to 200MPa. Such a high injection pressure can significantly improve the mixing quality of diesel and air, shorten the ignition delay period, make combustion more rapid and thorough, and control the combustion temperature, thereby reducing exhaust emissions.

1.3.2 Independent injection pressure control

The injection pressure of the fuel supply system of a traditional diesel engine is related to the rotational speed load of the diesel engine. This characteristic is detrimental to fuel economy and emissions under low-speed and partial load conditions. If the fuel supply system has the ability to control the injection pressure independently of rotational speed and load, the most suitable injection pressure can be selected to optimize the injection duration and ignition delay period, so as to minimize the exhaust emissions of the diesel engine under various operating conditions and achieve the best economy.

1.3.3 Improve the fuel economy of diesel engines

Users are very concerned about the fuel consumption rate of diesel engines. Measures such as high injection pressure, independent injection pressure control, small injection holes, and high average injection pressure can all reduce fuel consumption rates, thereby improving the fuel economy of diesel engines.

1.3.4 Independent fuel injection timing control

Injection timing directly affects the amount of oil injected into the cylinder before the top dead center of the diesel engine piston, determining the peak burst pressure and maximum temperature of the cylinder. High cylinder pressure and temperature can improve fuel economy, but they lead to an increase in NOX. The ability to control injection timing without relying on rotational speed and load is a key measure to achieve the best balance between fuel consumption rate and emissions.

1.3.5 Variable pre-injection control capability

Pre-injection can reduce particulate emissions without increasing NOX emissions. It can also improve the cold start performance of diesel engines, reduce white smoke emissions under cold conditions, lower noise, and enhance low-speed torque. However, the requirements for the pre-injection volume and the time interval between pre-injection and main injection vary under different working conditions. Therefore, having variable pre-injection control capabilities is highly beneficial to the performance and emissions of diesel engines.

1.3.6 The ability to control the minimum oil volume

The ability of the fuel supply system to have high injection pressure conflicts with the small fuel volume control capability required for diesel engine idle speed. When the fuel supply system has the pre-injection capability, its ability to control small fuel volumes will be further reduced. Due to the complex working conditions of diesel engines used in construction machinery, idle conditions often occur, while electronic fuel injection diesel engines are easier to achieve minimum fuel quantity control.

1.3.7 Rapid fuel cut-off capability

At the end of the injection, the fuel supply must be cut off quickly. If it cannot be cut off quickly, the diesel injected at low pressure will emit black smoke due to incomplete combustion, increasing HC emissions. The high-speed electromagnetic switch valve adopted on the fuel injector of the electronic fuel injection diesel engine can easily achieve rapid fuel cut-off.

1.3.8 Reduce the impact load of driving torque

The fuel injection system operates under very high pressure, which not only increases the average torque required by the drive system but also intensifies the impact load. The ability of the fuel injection system to smoothly load and unload the drive system is a criterion for measuring the injection system. The high-pressure common rail technology in electronic fuel injection diesel engine technology has significantly reduced the impact load of driving torque.

The purpose and advantages of electronic control technology for diesel engines

2.1 Purpose

Optimize power performance, improve fuel economy, control emissions, so that diesel engines can achieve the best working condition from idle speed to rated speed, prevent possible dangerous operating conditions, and extend the service life of parts.

2.2 Advantages

2.2.1 It has multi-functional automatic adjustment performance

The operating conditions of diesel engines used in construction machinery are variable, and they have high requirements for fuel consumption, emissions and reliability. The application of automatic control technology in the regulating system of diesel engines can precisely achieve multi-functional automatic regulation, thereby ensuring that the performance of diesel engines, such as power, fuel economy, reliability and ease of operation, is fully exerted.

2.2.2 Reduce weight, shrink size and enhance the compactness of diesel engines

For modern high-speed diesel engines, due to the large torque driving the fuel injection pump, it is very complex to design a compact and reliable fuel supply advance automatic regulator, and it is also rather difficult in the overall layout of the diesel engine. The adoption of automatic control technology to solve the problem of automatic adjustment of fuel supply advance Angle not only easily resolves the aforementioned challenges but also enhances the compactness of diesel engines.

2.2.3 The installation and connection of components are convenient, which improves maintainability

By adopting an automatic control system, the size of related components is reduced (especially in the fuel supply system), the installation site is free from spatial position constraints, the connection is simple, and it is conducive to the daily maintenance and repair of diesel engines.

2.2.4 Expanded functions such as fault diagnosis and communication

By adopting an automatic control system, it can be conveniently connected to a microcomputer, making it easy to implement the functions of diesel engine performance detection and fault diagnosis. Issues such as the storage and transmission of diesel engine operation and detection data are also easily solved, facilitating scientific management and use.

2.2.5 Enable more precise matching of the power output and load of the diesel engine

With the rapid development of construction machinery manufacturing technology, in order to enhance the operational efficiency of self-propelled construction machinery, automatic control devices such as electronic fuel injection diesel engines and electronically controlled automatic transmissions have been adopted. This enables self-propelled construction machinery to automatically adjust power output and power transmission within a certain range in response to load changes during operation, achieving a more precise match between the power output of the diesel engine and the load. Give full play to the operational efficiency of construction machinery.

The characteristics of diesel engine electronic control technology

Diesel engine electronic control technology shares many similarities with gasoline engine electronic control technology. The entire system is composed of three parts: sensors, electronic control units, and actuators. The main difference between diesel engines and gasoline engines in terms of electronic fuel injection is that the electronic fuel injection system of a gasoline engine only controls the air-fuel ratio (the ratio of gasoline to air), while the electronic fuel injection system of a diesel engine regulates the output fuel volume by controlling the fuel injection time Moreover, the fuel injection control of a diesel engine is determined by the engine's rotational speed and the position of the accelerator pedal (the position of the throttle and the fuel supply lever). Diesel engine electronic control technology has two distinct features: one is the complexity of diesel injection electronic control actuators, and the other is the diversity of diesel electronic control injection systems.

3.1 Diesel engines are a type of power machinery with relatively high thermal efficiency

Diesel engine fuel injection features high pressure, high frequency and pulsation. Its injection pressure can reach up to 200MPa, which is more than a hundred times that of a gasoline engine. It is much more difficult to implement electronic control of fuel injection volume in the high-pressure fuel injection system. Moreover, diesel injection has very high requirements for the precision of injection timing. The angular position relative to the top dead center of the diesel engine piston is much more accurate than that of gasoline engines. This leads to the electronic control actuator of diesel injection being much more complex.

3.2 Due to the diverse forms of diesel engine injection systems

Traditional diesel engines have systems with completely different structures, such as in-line pumps, distribution pumps, pump injectors, and single-cylinder pumps. The actuator for implementing electronic control technology is rather complex, which has led to the diversification of diesel injection systems. At the same time, diesel engines need to comprehensively control multiple parameters such as fuel volume, timing, and fuel injection pressure, and the difficulty of their software components is also greater than that of gasoline engines.

Classification of electronically controlled diesel injection systems

The first technology to emerge was the electronically controlled fuel injection pump technology. Later, the electronically controlled pump nozzle technology and high-pressure common rail injection technology were developed. The latter two technologies are currently the most important electronically controlled injection technologies for diesel engines. Among them, the fuel injection pressure of the electric control pump nozzle technology is extremely high, reaching up to 200MPa. Moreover, the pump and nozzle are installed together, so only a very short high-pressure oil guiding section is needed. The pump nozzle system can also achieve a very small pre-injection volume. Its fuel injection characteristics are triangular and it adopts segmented pre-injection. This is very much in line with the requirements of diesel engines (Volkswagen's TDI engine uses this technology). However, the fuel injection pressure of the electronically controlled pump nozzle technology is affected by the diesel engine speed. The high-pressure common rail technology using a pressure storage system can solve this problem. Its fuel injection pressure is lower than that of the pump nozzle system and can reach 160MPa. Some companies have recognized its wide range of fuel injection pressure adjustment for engines with any number of cylinders and gradually expanded its application scope (the earliest cars to use high-pressure common rail were Alfa Romeo 156 and Mercedes-Benz C-class cars).