Electronic fuel injectors are a critical and complex component in common rail systems.

Electronic fuel injectors are a critical and complex component in common rail systems.

Fuel injectors are precision devices requiring extremely high machining accuracy, demanding a wide dynamic flow range, strong resistance to clogging and contamination, and excellent atomization performance. The injector receives injection pulse signals from the ECU and precisely controls the fuel injection quantity.

The spray characteristics of the injector include atomization particle size, fuel mist distribution, fuel jet direction, range, and diffusion cone angle. These characteristics must meet the requirements of the diesel engine combustion system to ensure optimal air-fuel mixture formation and combustion, resulting in high power and thermal efficiency.

Electrically controlled fuel injectors are the most critical and complex component in the common rail system, and also the most challenging to design and manufacture. The ECU controls the opening and closing of solenoid valves to inject fuel from the high-pressure fuel rail into the combustion chamber with optimal injection timing, quantity, and rate. To achieve effective injection start point and precise injection quantity, common rail systems employ dedicated injectors with hydraulic servo systems and electronic control components (solenoid valves).

A fuel injector consists of a nozzle similar to a traditional fuel injector, a hydraulic servo system (controlling the piston, metering orifice, etc.), and a solenoid valve.

The diesel engine fuel injection system atomizes fuel and distributes it within the combustion chamber to mix with air.

It mainly consists of the nozzle and the injector body. Its mounting position and angle on the cylinder head depend on the combustion chamber design.

Fuel injectors are divided into open and closed types. Open injectors have a simple structure but poor atomization and are rarely used. Closed injectors are widely used in various diesel engines. During the intake stroke, a diesel engine draws in pure air. Near the end of the compression stroke, the fuel pressure is increased to over 100 MPa by the injection pump and injected into the cylinder through the injector. It mixes with the compressed, high-temperature air in a very short time to form a combustible mixture. Because diesel engines have a high compression ratio (typically 16-22), the air pressure inside the cylinder at the end of compression can reach 3.5-4.5 MPa, and the temperature can reach 750-1000 K (while the air-fuel mixture pressure in a gasoline engine at this time is 0.6-1.2 MPa, and the temperature reaches 600-700 K), greatly exceeding the auto-ignition temperature of diesel fuel. Therefore, after diesel fuel is injected into the cylinder, it mixes with air and immediately ignites and burns. The air pressure inside the cylinder rises rapidly to 6-9 MPa, and the temperature rises to 2000-2500 K. Driven by the high-pressure gas, the piston moves downward and drives the crankshaft to rotate, thus performing work. The exhaust gas is also discharged into the atmosphere through the exhaust pipe.

[1] Ordinary diesel engines are driven by the engine camshaft, and diesel fuel is delivered to the fuel chambers of each cylinder by means of a high-pressure oil pump. This fuel supply method varies with the engine speed and cannot achieve the optimal fuel supply at various speeds. The common rail injection system consists of a high-pressure fuel pump, a common fuel line, injectors, an electronic control unit (ECU), and several pipeline pressure sensors. Each injector in the system is connected to the common fuel line via its own high-pressure fuel line, which acts as a hydraulic accumulator for the injectors.

During operation, the high-pressure fuel pump delivers fuel to the common fuel line at high pressure. The high-pressure fuel pump, pressure sensors, and ECU work in a closed loop, achieving precise control of the fuel pressure within the common fuel line, completely eliminating the phenomenon of fuel pressure varying with engine speed. Its main characteristics are as follows:

1. Injection timing and fuel metering are completely separated; injection pressure and the injection process are controlled in real-time by the ECU.

2. The injection pressure, injection start point, and duration of each cylinder can be adjusted according to engine operating conditions to achieve the optimal injection control point.

3. It can achieve very high injection pressures and can perform diesel pre-injection.

Compared to gasoline engines, diesel engines have lower fuel consumption (on average 30% lower than gasoline engines), and diesel fuel is cheaper, resulting in better fuel economy. Diesel engines generally operate at lower speeds and have higher torque than gasoline engines, but they are heavier, noisier during operation, have higher manufacturing and maintenance costs, and produce worse emissions. However, with the development of modern technology, these disadvantages of diesel engines are gradually being overcome.