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Inspection and Maintenance of Diesel Fuel Injector

The fuel injector is one of the most important devices in the fuel supply system of the diesel engine, which can spray the diesel oil into the cylinder uniformly, finely and evenly to make it mix with the compressed air in the cylinder evenly and form a good combustible mixture. Its working quality directly affects the power, economy and service life of diesel engines. In the process of using and maintaining the diesel engine, some minor negligence may lead to major faults.


1 Injector detection

The performance index of fuel injector mainly includes the following three items:

(1) inspection of fuel injection pressure. If the injection pressure does not meet the standard, it will seriously affect the power and economy of the diesel engine. If the injection pressure is too low, the oil beam velocity, range and spray cone angle will be reduced, which will make the diesel atomization not good and produce the phenomenon of dropping oil. At the same time, it will cause the injection time to advance and the injection quantity to increase after the end of the injection. This will result in incomplete combustion, black smoke from the exhaust gas, carbon deposition, and fuel injector seizure. On the contrary, if the injection pressure is too high, the diesel leakage will increase, the injection duration will shorten, the injection amount will decrease and the diesel engine will work rough. At the same time, it will increase the wear of the fuel injector and other related parts. The injector injection pressure check can be performed on the diesel engine. Connect a tee joint to the outlet pipe of the high-pressure oil pump, and connect the other two ends with the standard injector (the same model as the injector to be tested, and the injection pressure is the standard value) and the injector to be tested. The diesel engine is turned over and the fuel is supplied by the high-pressure oil pump. If the two injectors simultaneously spray oil and the spray quality is the same, the fuel injector is qualified. If the tested injector injects fuel first, it means that the injection pressure is low, then tighten the pressure regulating nut until the two injectors inject fuel at the same time.


(2) Check the injection advance angle. The injection advance angle is different from the supply advance angle. The fuel supply advance angle refers to the crankshaft angle from the piston position of the first cylinder to the top dead center when the first cylinder plunger pair of the fuel injection pump starts to supply oil. The fuel injection advance angle refers to the crankshaft angle from the piston position of the first cylinder to the TDC when the fuel injector of the first cylinder starts to inject fuel into the cylinder. Obviously, the injection advance angle is smaller than the oil supply advance angle, generally less than about 8 °C. This is related to the structure of the injection pump and the length of the high-pressure oil pipe.

(3) spray quality inspection. It is mainly to check whether the fuel injector can inject the diesel oil into a fine and uniform spray under the specified pressure. The inspection shall be carried out on the fuel injector calibrator, and the pump oil handle shall be pressed at the speed of 80-100 times per minute to observe whether the injected oil beam is normal, and the atomization quality shall meet the requirements.

2 Precautions for disassembly and repair

(1) Carefully dismantle the fuel injector, and ask the maintenance personnel not to dismantle the fuel injector blindly, and operate in strict accordance with the operating procedures. When the fuel injector is repaired, it often happens that the quality of the sprayer with good atomizing quality is deteriorated after being disassembled, cleaned and reassembled. This is because the sealing ring belt between the needle valve cone of the nozzle and the cone hole of the valve body of the nozzle has been worn, but it is still sealed well. Once it is disassembled and reassembled, the original well-sealed fitting position of the needle valve in the needle valve body is damaged. Therefore, it should not be disassembled without inspection of the injector tester and confirmation of disassembly.


(2) When the fuel injector is installed after replacement, cleaning or troubleshooting, the appropriate thickness of the sealing adjusting pad shall be selected according to the requirements of technical conditions to ensure the depth of the fuel injector into the combustion chamber.So as to ensure the formation quality of the combustible mixture.When assembling the fuel injector after cleaning and troubleshooting, make sure that the coupling parts are used in pairs. The spray needle and nozzle are all components with grinding matching, and the matching clearance is 0.002-0.004 mm.In case of any pairing, the sealing between the spray needle and the nozzle will be affected.When assembling the injector, the impurities in the inner cavity of the nozzle shall be completely removed to prevent the injector from sticking (the upper clamp is not sealed, and the lower clamp is not injected).

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