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What are the main types of common diesel generator set injectors?

June 28, 2022
Injector is an important part of the fuel supply system of diesel generator set. Its function is to spray the high pressure diesel fuel sent by the injection pump to the combustion chamber in the form of mist and form a good combustible mixture with the compressed air in the combustion chamber. Therefore, the basic requirements of the injector work are: a certain injection pressure and range, as well as the appropriate spray cone angle, good spray, at the end of the injection can quickly stop spraying, no drip phenomenon. At present, diesel generator sets often use the closed type injector hole type injector and shaft needle type injector.
Hole type injector
Hole type injector is mainly used in direct injection diesel engine, according to the form of injector nozzle is divided into long type and short type, the number of injection holes is 1 ~ 8, the diameter of the injection hole is 0.15 ~ 0.7mm, it consists of needle valve, needle valve body, top bar, regulating spring, regulating screw and injector body.
Injector nozzle (including needle valve and needle valve body), also known as needle valve coupling, made of high-quality alloy steel (GCr15), and by heat treatment and optional grinding into pairs, so they can not be interchanged. The clearance is 0.001~0.0015mm, which should ensure both good sliding and no oil leakage. Needle valve has two cone surface, the lower cone surface and the valve body with the corresponding inner cone surface, known as the sealing cone surface to seal the injector cavity; the central cone surface in the annular oil cavity of the valve body to withstand the axial thrust of oil pressure to make the needle valve rise, known as the pressure-bearing cone. Needle valve body has an annular oil groove and oil channel hole at the upper end, and an oil cavity and spray hole at the lower end. Needle valve coupling with tight cap fastened in the injector body, regulating spring through the top bar to make the needle valve pressed in the valve seat, needle valve and the top bar contact surface into a spherical surface, can prevent the top bar bending and the needle valve to generate lateral pressure. The spring force of the regulating spring can be adjusted by the regulating screw and locked with the regulating nut after adjustment.
The working principle of the closed injector as shown in 1-2, the high pressure diesel fuel from the injection pump through the injector body and the needle valve body of the oil channel into the oil cavity, as the spray hole is closed by the needle valve, the pressure of diesel fuel in the cavity will rise rapidly. When the diesel pressure acting on the pressure-bearing cone of the needle valve is greater than the spring force of the regulating spring, the needle valve will rise along the axial direction, the spray hole is opened, so the high-pressure diesel fuel through the spray hole began to spray into the combustion chamber. Due to the throttling effect of the spray hole, the diesel fuel is sprayed out to form a mist of fine particles, and air quickly open into a combustible mixture. This injection process has continued until the injection pump to stop supplying oil, and in the injector cavity oil pressure is lower than the regulating spring force, the needle valve under the action of the regulating spring immediately close the spray hole, the injection only stops.
Closed injector injection pressure mainly depends on the regulating spring force, therefore, adjust the size of the regulating spring force can directly change the size of the injection pressure. When the adjusting screw is rotated inward, the spring tightening force increases, and the injection pressure increases; conversely, the injection pressure decreases. Needle valve lift is limited by the lower surface of the injector body and the regulating spring force, so the maximum lift of the injector needle valve is 0.45mm to ensure rapid disconnection. Injector in the work period, a small amount of diesel oil from the needle valve and the valve body leakage, through the return pipe flow back to the diesel filter or tank, while the needle valve coupling to play a role in lubrication.
Shaft needle type injector
Shaft needle type injector is characterized by a single hole, a large aperture, generally 1 ~ 3mm. needle valve end has a certain shape of the pin (shaft needle), inserted into the spray hole, and the spray hole constitute a very small ring gap (about 0.013 ~ 0.025mm), high pressure diesel fuel through this gap spray. The shape of the shaft needle has a cylindrical and inverted cone, as shown in Figure 1-3. The sprayed diesel fuel produces different spray conditions according to different shaft needle shapes. The advantage of this injector is that the shaft needle moves up and down in the spray hole, which can improve the spray and clear the carbon by itself, so that the spray hole is not easily blocked and the workability of the diesel generator set is improved.