s are generally divided into two types: open and closed. Automotive diesel engines widely use closed fuel injectors, which are composed of a fuel injector body, a pressure regulating device, and a fuel injector. The fuel injection nozzle of the closed fuel injector is a pair of precision parts, composed of a needle valve and a needle valve body. Generally, the needle valve is made of high-speed steel with good thermal stability, and the needle valve body is made of high-quality alloy steel with impact resistance. After finishing and matching grinding, their matching clearance is extremely small, only 0.002～0.004mm. According to the different structure of fuel injectors, closed fuel injectors are divided into three types: hole injector, pin injector and low inertia injector. The first two applications are more common.