Fault Modes of Diesel Engine Mechanical Fuel Injection System 2

This article continues to introduce the main factors that cause diesel engine failures in the mechanical fuel injection pump fuel supply system of diesel engines.

3. Diesel generator injector needle valve components: Needle valve components are prone to malfunction during operation due to the erosion of high-pressure diesel and high-temperature gas, grinding of mechanical impurities, and impact of needle valve springs.

a. Wear of needle valve components (fuel injectors): The parts where needle valve components often wear are the sealing cone surface, needle valve guide part, and the inverted cone that plays a role in atomization. The wear of the sealing cone surface is caused by the impact of the fuel injector spring and the scouring effect of impurities in diesel. After the wear of the sealing cone surface, the sealing performance deteriorates, causing the pressure in the pressure chamber at the head of the fuel injection nozzle to not increase, resulting in poor atomization and oil dripping, causing black smoke and carbon deposition at the head of the fuel injection nozzle in the diesel engine. In addition, when the sealing performance of the fuel injector deteriorates, high-pressure gas can easily enter the interior of the injector, and in severe cases, it can burn out the injector or cause fuel coking, causing the needle valve to jam.

The wear of the needle valve and fuel injector guide part is caused by the grinding effect of impurities brought in by diesel. Most of the wear occurs at the lower end of the guide section. If the wear is severe, it will increase the return oil volume of the fuel injector, reduce the fuel supply, decrease the injection pressure, delay the injection time, etc., causing a decrease in diesel engine power and even inability to work under load.

b. Needle valve jamming: The main reasons for needle valve jamming include blockage due to nozzle overheating, deformation of the needle valve, and poor cooling in diesel engines with excessive load, high working temperature, and poor cooling; If the lift of the needle valve is too long, the seating time will be extended. Before seating, the diesel pressure in the inner chamber is lower than the pressure in the cylinder, so gas will flow back into the inner chamber from the injection hole, causing the needle valve to jam; The needle valve inside the fuel injector is stuck due to impurities brought in by diesel or severe carbon accumulation near the injection hole; The fuel injector spring becomes soft or the fuel injection pressure is adjusted too low, causing the needle valve to not close in time, gas to enter the nozzle, causing the needle to burn out, deform, and become stuck.

If the needle valve gets stuck when it is in the open state, the fuel spray from the fuel injector will not atomize well, and the combustion will not be complete, resulting in black smoke; At the same time, unburned fuel will also flush the oil on the cylinder wall, accelerating the wear of cylinder liners and other parts.

If the needle valve gets stuck in the closed state, no matter how high the pressure of the fuel injection pump is, it cannot open the needle valve, making the cylinder unable to work, and causing the fuel injection pump to make noise due to high pressure, or even damage the fuel injection pump, causing the high-pressure fuel pump to vibrate.

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