The fuel of a diesel engine is injected into the cylinder near the end of the compression process. The function of the fuel injector in a diesel generator set is to atomize the fuel into fine particles and distribute them appropriately in the combustion chamber, forming a good combustible mixture. Therefore, the basic requirements for the fuel injector are: a certain injection pressure, a certain range, a certain spray cone angle, good spray, quick fuel stop at the end of fuel injection, and no fuel dripping.
The hole type fuel injector of diesel generator set is mainly used in direct injection diesel engines. Due to the number of spray holes and small aperture, it can spray several spray columns with small cone angles and longer range. The general number of fuel injection holes is 2-8, with a diameter of 0.15-0.50mm. The number and direction of spray holes depend on the requirements of various combustion chambers for atomization quality and the arrangement of injectors in the combustion chamber. For example, the combustion chamber of the 6135G diesel engine is W-shaped, and the formation of the mixture is mainly achieved by directly injecting fuel into the combustion chamber space, so a 4-hole closed injector is used. The nozzle diameter is 0.35mm, the injection angle is 150 degrees, the needle valve opening pressure is 17.5MPa, and the nozzle shape is suitable for the W-shaped combustion chamber.
The main components of fuel injectors are needle valves and needle valve bodies made of high-quality alloy steel, collectively known as needle valve fittings (also known as fuel injector fittings). The cylindrical surface on the upper part of the needle valve is in high-precision sliding fit with the corresponding inner cylindrical surface of the needle valve body, with a clearance of about 0.001-0.0025mm. This gap must be within the specified range. If the clearance is too large, oil leakage may occur, which will reduce the oil pressure and affect the quality of spray; If the gap is too small, the needle valve cannot slide freely. The conical surface of the lower part of the needle valve is fully exposed in the annular oil chamber of the needle valve body. Its function is to withstand the axial thrust caused by oil pressure and make the needle valve rise, so this conical surface is called the pressure bearing conical surface. The conical surface at the lower end of the needle valve is matched with the corresponding inner conical surface on the needle valve body to achieve sealing of the injector cavity, which is called the sealing conical surface. The cylindrical surface at the top and conical surface at the bottom of the needle valve, along with the corresponding mating surface on the needle valve body, are finely ground and then mutually ground to ensure their mating accuracy. Therefore, the selected and ground needle valve components cannot be interchanged.
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