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Cause Analysis and Solution of Diesel Engine Fuel Injector Failure

May 17, 2022
The diesel fuel injector is installed on the cylinder head, and its function is to inject diesel oil into the combustion chamber with finer atomized particles to form a good flammable mixture with the air. Working for a long time in the environment, the internal moving parts are subjected to the impact of high-speed flowing fuel and repeated scouring of small mechanical impurities in the fuel, which is extremely easy to wear and corrode. It is one of the most faulty components in the diesel engine fuel system. Today, JUNVOCH, a diesel generator set manufacturer, will introduce the cause analysis and solution to the failure of the diesel injector.
1. Poor atomization of the injector
When the injection pressure is too low, the nozzle holes are worn with carbon deposits, the end face of the spring is worn or the elastic force is reduced, it will cause the injector to open in advance, delay to close, and cause the phenomenon of poor injection atomization.
If it is a single-cylinder diesel engine, it will not work; if it is a multi-cylinder diesel engine, the power will drop, the exhaust will emit black smoke, and the sound of the machine will not be normal. In addition, because the diesel droplets with too large particle size cannot be fully burned, they will flow into the oil accumulation pan along the cylinder wall, which will increase the oil level of the oil, decrease the viscosity, and deteriorate the lubrication, which may also cause the accident of burning the Vara cylinder.
Solution: The injector should be disassembled for cleaning, overhaul and re-commissioning.
2. The fuel injector return pipe is damaged
When the needle valve coupler is seriously worn or the needle valve body and the injector housing are not closely matched, the fuel return volume of the injector increases significantly, and some can reach 0.1-0.3kg/h. If the oil return pipe is damaged or missing, the return oil will be lost in vain, resulting in waste.
Therefore, the oil return pipe must be intact and installed airtight so that the return oil can flow into the tank smoothly. If the oil return pipe is connected to the diesel filter, a check valve should be set at the terminal to prevent the diesel oil in the filter from flowing back into the injector.
3. Needle valve nozzle expansion
Due to the continuous injection and scouring of the high-pressure oil flow, the nozzle hole of the needle valve will gradually become larger, resulting in a drop in the injection pressure, a shortened injection distance, poor diesel atomization, and an increase in the carbon deposition in the cylinder.
Solution: The hole diameter of the single-hole shaft needle injector is generally larger than 1mm. A steel ball with a diameter of 4-5mm can be placed at the end of the hole and tapped lightly with a hammer to make the injection hole locally plastically deform and reduce the hole diameter. Due to the large number of holes and the small hole diameter of the multi-hole direct injection injector, the punching sample made of high-speed steel can only be tapped lightly at the end of the hole. If it is still unqualified after debugging, the needle valve coupler should be replaced.
4. The needle valve bites
Moisture or acidic substances in diesel oil will cause the needle valve to corrode and be stuck. After the sealing cone surface of the needle valve is damaged, the combustible gas in the cylinder will also enter the mating surface to form carbon deposits, which will cause the needle valve to bite and cause the injector to die. The fuel injection effect is lost, causing the cylinder to stop working.
Solution: You can put the needle valve pair in waste oil and heat it until it boils and smokes, then take it out, clamp the tail of the needle valve with hand pliers cushioned with a soft cloth and move it slowly, pull it out and stain it with clean oil to let it go. The needle valve moves and grinds repeatedly in the valve body until the needle valve can slowly withdraw from the valve body when the needle valve coupler is inverted. If the fuel injector test fails, the needle valve coupler should be replaced.
5. End face wear of needle valve body
The end face of the needle valve body is impacted by the frequent reciprocating motion of the needle valve, and a pit will gradually form over time, thereby increasing the lift of the needle valve and affecting the normal operation of the injector.
Solution: The needle valve body can be clamped to the grinding machine to grind the end face, and then grind it on the glass plate with fine grinding paste.
6. Air leakage and oil leakage from the joint hole of the injector and the cylinder head
When the fuel injector is installed on the cylinder head, the carbon deposits in the installation holes should be carefully removed, and the copper gasket must be flat, and must not be replaced with asbestos plates or other materials to prevent poor heat dissipation or failure to seal.
If the copper gasket is made by itself, it must be processed with red copper according to the specified thickness to ensure that the distance from the injector to the plane of the cylinder head meets the technical requirements. In addition, the concave shape of the fuel injector pressure plate should be installed downward. When tightening, it should not be biased on one side. It should be tightened evenly according to the specified torque, otherwise the fuel injector head will leak and leak oil due to deformation and deflection.
7. Needle valve and needle valve hole guide surface wear
The needle valve frequently reciprocates in the needle valve hole, coupled with the intrusion of impurities and dirt in the diesel oil, the guide surface of the needle valve hole will gradually wear, so the gap increases or scratches appear, resulting in increased internal leakage of the injector and increased pressure. If it is lowered, the fuel injection amount is reduced, and the fuel injection time lags, which makes the diesel engine difficult to start.
Solution: When the fuel injection time delay is too long, the locomotive cannot even run, and the needle valve coupler should be replaced at this time.
8. The injector appears dripping oil
When the fuel injector is working, the sealing cone of the needle valve body will be frequently and strongly impacted by the needle valve. In addition, the high-pressure oil flow is continuously sprayed from there, and the cone surface will gradually appear nicks or spots, thereby losing the seal, causing Fuel injector dripping.
When the temperature of the diesel engine is low, the exhaust pipe emits white smoke, and when the engine temperature rises, it turns into black smoke, and the exhaust pipe emits an irregular blasting sound. If the fuel supply to the cylinder is stopped at this time, the smoke exhaust and the sound of gun blasting will disappear.
Solution: The fuel injector can be disassembled, and a little chromium oxide fine grinding paste is applied to the head of the needle valve (be careful not to stick it in the needle valve hole) to grind the cone surface, then wash it with diesel oil, and put it into the fuel injector for testing. . If it is still unqualified, the needle valve coupler needs to be replaced.