Electronically controlled diesel injection system

In order to improve the operation performance of diesel engine and reduce the fuel consumption rate, and also to meet the needs of strict diesel engine emission standards, since the early 1980s, a variety of electronically controlled diesel injection systems have come out one after another.

Three stages of electronically controlled fuel injection system
Electronically controlled fuel injection system is the most important one in the electronic control system of diesel engine. In the process of development, there are three stages of position control, time control and pressure-time control electronically controlled fuel injection system.

1. Position control type electronic control fuel injection system
The first generation of electronic fuel injection system completely retains the basic structure of the traditional fuel system. By adding a control system composed of sensors, actuators and microprocessors, it controls the position of the rack or sliding sleeve of the fuel pump, thus controlling the fuel injection amount of the fuel injection system and improving the control ability and adaptability of the fuel injection system.

2. Time control type electric control fuel injection system
The second generation of electronically controlled fuel injection system mainly controls the opening and closing time of the high-speed solenoid valve, controls the amount of fuel supply through the opening time of the solenoid valve, and can directly control the fuel injection process of the diesel engine. According to the different devices that generate high pressure, it can be divided into distribution pump type, in-line pump type (see diesel engine fuel supply system), pump nozzle type (see diesel engine pump nozzle) and single pump type (see diesel engine single pump) electronic control diesel injection.

3. Pressure-time control type electric control fuel injection system
The third generation of electronically controlled fuel injection system is represented by the high-pressure common rail fuel injection system, which innovates the main basic components of the traditional fuel system. Its characteristics are that the generation process of fuel injection pressure has nothing to do with the fuel injection process, and the high-speed powerful solenoid valve is used to control the fuel injection start point and injection amount independently, flexibly and accurately.

Advantages of Common Rail Fuel Injection System
The diesel oil is sucked out from the oil tank by the low-pressure oil pump and is supplied to the high-pressure oil pump after being filtered, a solenoid valve is arranged in the low-pressure oil pump to control the fuel oil to reach the high-pressure oil pump chamber, and the fuel oil enters the tubular pressure accumulator-fuel rail. A pressure sensor on the common rail monitors the fuel pressure from time to time and transmits the signal to the ECU to control the fuel pressure in the common rail to reach the desired value by adjusting the flow.The injection pressure varies from 200 to 1800 bar according to the operating conditions of the engine, and then it is injected into the cylinder by computer control. The common rail not only maintains the fuel pressure, but also eliminates the pressure fluctuation.

Fuel injection is a complex combination of mechanical, hydraulic and electronic systems. In order to adapt to the working environment of the engine under various working conditions, the fuel must be filtered and pressurized before combustion, and injected into each cylinder at a certain injection rate at an accurate time. The engine computer controls the exhaust gas recirculation, supercharging, and exhaust aftertreatment systems for optimum engine performance and exhaust emissions.

New generation common rail engine
Diesel common rail system has been developed for three generations, and it has strong technical potential.
The first-generation common-rail high-pressure pump was always kept at the highest pressure, resulting in a waste of energy and high fuel temperatures. The second generation can change the output pressure according to the engine demand, and has the function of pre-injection and post-injection. Pre-injection reduces engine noise: a small amount of fuel is injected into the cylinder for compression ignition one millionth of a second before the main injection, pre-heating the combustion chamber.The preheated cylinder makes the compression ignition after main injection easier, and the pressure and temperature in the cylinder no longer increase suddenly, which is conducive to reducing combustion noise. In the expansion process, post-injection produces secondary combustion, which increases the temperature in the cylinder by 200 to 250 degrees Celsius and reduces the hydrocarbons in the exhaust gas.

Because of its strong technical potential, today manufacturers have set their sights on the third generation of the common rail system, the piezo-electric (piezo) common rail system, which replaces the solenoid valve with a piezoelectric actuator, thus achieving more precise injection control. Without the oil return pipe, the structure is simpler. The pressure is elastically adjusted from 200 to 2000 bar. The minimum injection amount can be controlled at 0.5mm3, and the smoke and NOX emission are reduced.