In the past, the diesel engine used mechanical diesel nozzle, which worked by controlling the precision coupling parts (needle valve and needle valve body). Nowadays, the fuel injection nozzle for motorcycles and automobiles is actually a simple solenoid valve. When the solenoid coil is energized, the suction force is generated, and the needle valve is sucked up to open the injection hole. The fuel is ejected at high speed through the annular gap between the needle and the injection hole on the head of the needle valve, forming a mist, which is conducive to combustion and charging.

The injector itself is a normally closed valve. Normally closed valve means that the valve is always closed when no control signal is input; while normally open valve means that the valve is always open when no control signal is input). According to the control mode of solenoid valve coil, injector can be divided into voltage driven and current driven.

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Voltage drive means that the electric pulse voltage driving the fuel injector is constant. This kind of injector can be divided into high impedance type and low impedance type. The low impedance type injector is driven by 5-6v voltage, and the resistance of electromagnetic coil is 3-4 Ω. It can not be directly connected with 12V power supply, otherwise the electromagnetic coil will be burned. High impedance injector is driven by 12V voltage, and the electromagnetic coil is driven by 12V voltage The resistance is high, which is 12-16 Ω. A valve needle moves up and down to control the opening and closing of the valve.

When the ECU sends the fuel injection command, its voltage signal will make the current flow through the coil in the fuel injection nozzle, which will generate a magnetic field to suck up the valve needle and open the valve so that the oil can be ejected from the injection hole.

The performance of the engine is determined by the working quality of the fuel injection nozzle. The fuel injection nozzle is partially blocked due to dirty fuel, which will cause serious carbon deposit in the cylinder; accelerated wear of cylinder barrel and piston ring causes unstable idle speed, increased fuel consumption, weak acceleration, difficult starting and excessive emission, which will completely block the fuel injection nozzle and damage the engine.