The electronically controlled fuel injector is a key and complex component in the common rail system

The fuel injector is a precision component with extremely high processing accuracy, which requires a wide dynamic flow range, strong anti-clogging and anti-pollution capabilities, as well as good atomization performance. The fuel injector receives the fuel injection pulse signal sent by the ECU and precisely controls the fuel injection volume.

The spray characteristics of fuel injectors include atomization particle size, oil mist distribution, oil beam direction, range and diffusion cone Angle, etc. These characteristics should meet the requirements of the diesel engine combustion system to ensure the perfect formation and combustion of the mixture, and to achieve high power and thermal efficiency.

The electronically controlled fuel injector is the most crucial and complex component in the common rail system, and it is also the one with the greatest design and process difficulty. The ECU controls the opening and closing of the solenoid valve to inject the fuel in the high-pressure fuel rail into the combustion chamber at the optimal injection timing, injection volume and injection rate. To achieve an effective fuel injection starting point and precise fuel injection volume, the common rail system adopts a dedicated fuel injector equipped with a hydraulic servo system and electronic control components (solenoid valves).

The fuel injector is composed of a hole type fuel injector similar to the traditional fuel injector, a hydraulic servo system (control piston, control volume hole, etc.), solenoid valves, etc.

The fuel injection system of a diesel engine is a component that atomizes fuel and distributes it in the combustion chamber to mix with air.

It is mainly composed of fuel injectors and fuel injector bodies. Its installation position and Angle on the cylinder head depend on the design of the combustion chamber.

Fuel injectors are divided into open type and closed type. Open injectors have a simple structure, but they have poor atomization and are rarely adopted. Closed fuel injectors are widely used in various diesel engines. The diesel engine takes in pure air during the intake stroke. Near the end of the compression stroke, diesel is pressurized to over 100MPa by the fuel injection pump and injected into the cylinder through the fuel injector. In a very short time, it mixes with the high-temperature compressed air to form a combustible mixture. Due to the high compression ratio of diesel engines (generally 16-22), the air pressure inside the cylinder can reach 3.5-4.5MPa at the end of compression, and the temperature can be as high as 750-1000K (while the mixture pressure of gasoline engines at this time is 0.6-1.2MPa, and the temperature can reach 600-700K), which is much higher than the self-ignition temperature of diesel. Therefore, after diesel is injected into the cylinder, it immediately ignites and burns by itself after mixing with air in a very short time. The air pressure inside the cylinder rose rapidly to 6-9 mpa, and the temperature also increased to 2000-2500K. Driven by high-pressure gas, the piston moves downward and rotates the crankshaft to do work. The exhaust gas is also discharged into the atmosphere through the exhaust pipe.

[1] A common diesel engine is driven by the engine camshaft and uses a high-pressure oil pump to deliver diesel to the fuel chambers of each cylinder. This fuel supply method varies with the engine speed and cannot achieve the optimal fuel supply at all speeds.

The common rail injection fuel supply system consists of a high-pressure fuel pump, a common fuel supply pipe, fuel injectors, an electronic control unit (ECU), and some pipeline pressure sensors. Each fuel injector in the system is connected to the common fuel supply pipe through its own high-pressure fuel pipe, and the common fuel supply pipe plays a role in hydraulic pressure storage for the fuel injectors.

When in operation, the high-pressure fuel pump delivers fuel to the common fuel supply pipe at high pressure. The high-pressure fuel pump, pressure sensor and ECU form a closed loop to precisely control the oil pressure in the common fuel supply pipe, completely changing the phenomenon that the fuel supply pressure varies with the engine speed. Its main features are as follows in three aspects:

1. The fuel injection timing and fuel metering are completely separated, and the fuel injection pressure and process are controlled in real time by the ECU.

2. The fuel injection pressure of each cylinder, the starting point and duration of fuel injection can be adjusted according to the working condition of the engine, thereby pursuing the best control point of fuel injection.

3. It can achieve a very high fuel injection pressure and can also pre-inject diesel.

Compared with gasoline engines, diesel engines have a lower fuel consumption rate (on average 30% lower than gasoline engines), and diesel is cheaper, so they have better fuel economy. At the same time, the rotational speed of diesel engines is generally lower than that of gasoline engines, and their torque is greater than that of gasoline engines. However, they are heavier, produce more noise during operation, and are more difficult to manufacture

The maintenance cost is high, and the emissions are also worse than those of gasoline engines. However, with the development of modern technology, these shortcomings of diesel engines are gradually being overcome.