Function and Classification Of Fuel Injectors

The function of fuel injector

The fuel injector is one of the important components of the diesel engine fuel supply system. Its main function is to make the fuel under a certain pressure, it is sprayed into the combustion chamber in the form of mist and distributed reasonably so that it can be mixed with the air to form the most favorable combustible mixture for combustion.

According to the requirements of the formation and combustion of the mixture, the injector should have a certain injection pressure and range, injector pump provides pressure, appropriate spray cone angle and atomization quality; the injection should be stopped quickly, and no fuel leakage will occur, so as not to deteriorate the combustion process; the best injection The oil characteristics are that in the fuel supply process of each cycle, less fuel is injected at the beginning, more fuel is injected in the middle, and less fuel is injected at the later stage, so as to work softly and improve the combustion conditions in the later stage.

Composition Of Fuel Injectors

The closed fuel injector is provided with a needle valve fuel cut-off element between the high pressure fuel pipe and the nozzle hole. Under the action of the spring preload and the liquid pressure, the needle valve remains in the closed position, and only under the action of a certain fuel pressure It was opened to start injecting fuel. Closed injectors can be divided into hole type and pin type according to the structure of their injectors.

1) Hole injector

Hole fuel injector mainly used in diesel engines with direct injection combustion chambers. Generally, the number of injection holes is 1~8, and the diameter of injection holes is 0.2~0.8mm. The number and direction of injection holes depend on the effect of various combustion chambers on the spray quality. requirements and the arrangement of the nozzles in the combustion chamber.

The hole type injector is mainly composed of needle valve, needle valve body, ejector rod, pressure regulating spring, pressure regulating screw and injector body and other parts. The most important component in the injector is the nozzle. The most precise part of the nozzle is the needle valve coupler, which consists of the needle valve  and the needle valve body . The matching clearance is 0.002~0.004mm, and it needs to be ground after selection. Not interchangeable. The pressure regulating spring  installed on the upper part of the injector body presses the needle valve tightly against the sealing surface of the needle valve body through the ejector rod  to close the nozzle hole. 

2) Axial needle injector

The structure of the shaft needle injector is similar to that of the hole injector, but the nozzle head structure is different. The head of the shaft needle protrudes out of the nozzle hole, and its shape can be made into a cylinder or a cone. Injector Nozzle diameter is 1-3mm, form a circular slit with the pin.

The spray shape is hollow cylinder or cone, and the spray cone angle is 4°~6°. Because the object needle moves up and down in the hole, it has a self-cleaning effect, and it is not easy to deposit and block carbon, which improves the working reliability. The processing of the nozzle hole is also easy, but the concentricity between the pin and the hole is required to be high, otherwise an eccentric spray body will appear. It is suitable for swirl-type combustion chambers and pre-chamber combustion chambers that do not require high spray.