The function of the fuel injector is to atomize the diesel with a certain pressure into fine and uniform oil particles so that the diesel can be well mixed with the air in the combustion chamber.
The fuel injector is installed on the cylinder head, and the nozzle goes deep into the combustion chamber of the diesel engine. It works for a long time under high temperature, high pressure, and gas corrosion environment. The internal moving parts are subject to the impact of high-speed flowing fuel and the repeated friction of tiny mechanical impurities in the fuel, which is easily worn and corroded, it is one of the most malfunctioning parts in the diesel engine fuel system.
This article will briefly introduce the common faults and precautions of injectors.
Causes of diesel engine injector failure
1. Poor atomization of the injector
When the fuel injection pressure is too low, the nozzle hole wears and there are carbon deposits, the spring end surface is worn or the elastic force drops, it will cause the fuel injector to open in advance, delay the closure, and cause the phenomenon of poor fuel 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 is not normal. Besides, because the diesel mist droplets with too large particle size cannot be fully burned, they flow into the oil pan along the cylinder wall, which increases the oil level, decreases the viscosity, and deteriorates lubrication, which may also cause the burning of the cylinder.
Solution: The fuel injector should be disassembled and cleaned, repaired, and re-commissioned.
2. Damaged fuel injector return pipe
When the needle valve assembly is severely worn or the needle valve body and the injector housing are not closely matched, the oil return of the injector will increase significantly, and some can reach 0.1-0.3 kg/h. If the return pipe is damaged or missing, the return oil will be lost in vain, causing waste.
Therefore, the oil return pipe must be intact and sealed so that the oil return can flow smoothly into the oil tank. If the oil return pipe is connected to the diesel filter, its terminal should be equipped with a one-way valve to prevent the diesel in the filter from flowing back into the injector.
3. Needle valve nozzle enlarged
Due to the continuous injection and scouring of the high-pressure oil flow, the needle valve nozzle hole will gradually become larger, resulting in a decrease in the injection pressure, a shortened injection distance, poor diesel atomization, and increased carbon deposits in the cylinder.
Solution: The diameter of the single-hole shaft needle injector is generally larger than 1mm. A steel ball with a diameter of 4 to 5mm can be placed at the end of the hole and tapped lightly with a hammer to make the injection hole partially plastically deform and reduce the diameter. Due to a large number of holes and the small diameter of the multi-hole direct-injection injector, it can only be lightly tapped on the hole end with a punch made of high-speed steel. If it is still unqualified after debugging, the needle valve assembly should be replaced.
4. Needle valve stuck
Moisture or acid in diesel will cause the needle valve to rust and become stuck. After the needle valve sealing cone is damaged, the combustible gas in the cylinder will escape into the mating surface to form carbon deposits, causing the needle valve to seize, and the fuel injector will lose its fuel injection function, causing the cylinder to stop working.
Clamp the tail of the needle valve with pliers with a soft cloth to slowly move it, and then pull it out and moisten it with clean engine oil.
Solution: Put the needle valve assembly in the waste engine oil and heat it until it boils and smoke, and then take it out. Clamp the tail of the needle valve with pliers with a soft cloth to slowly move it, and then pull it out and moisten it with clean engine oil.
The needle valve moves and grinds repeatedly in the valve body until the needle valve can withdraw from the valve body slowly when the needle valve assembly is turned upside down. If the fuel injector fails the test, the needle valve assembly should be replaced.
5. The end face of the needle valve body is worn
The end face of the needle valve body is impacted by the frequent reciprocating movement of the needle valve, and pits will gradually form over time, which will increase the lift of the needle valve and affect the normal operation of the fuel injector.
Solution: The needle valve body can be clamped on a grinder to grind this end surface, and then a fine grinding paste is used to grind it on the glass plate.
6. Air leakage and oil leakage in the connecting hole of the fuel injector and the cylinder head
When installing the cylinder head on the injector, carefully remove the carbon deposits in the mounting hole. The copper gasket must be flat and must not be replaced by asbestos plates or other materials to prevent poor heat dissipation or failure to seal.
If the copper washer is made by yourself, it must be processed with red copper according to the specified thickness to ensure that the distance of the injector extending from the cylinder head plane meets the technical requirements.
Besides, the concave shape of the pressure plate of the injector should be installed downwards. Avoid unilateral bias when tightening. It should be evenly tightened according to the specified torque, otherwise, the injector head will be deformed and deflected and cause gas leakage.
7. The guide surface of the needle valve and the needle valve hole is worn
The frequent reciprocating movement of the needle valve in the needle valve hole, coupled with the intrusion of impurities and dirt in the diesel oil, will gradually wear the guide surface of the needle valve hole. Therefore, the gap increases or the scratches appear, which leads to the increase of the internal leakage of the injector, the decrease of the pressure, the decrease of the fuel injection amount, and the fuel injection time lag, causing difficulty in starting the diesel engine.
Solution: When the fuel injection time is delayed too much, the locomotive cannot even run, and the needle valve assembly should be replaced at this time.
8. Oil dripping from the injector
When the injector is working, the sealing cone of the needle valve body will be subject to frequent strong impacts from the needle valve. Coupled with the continuous injection of high-pressure oil flow from there, the cone surface will gradually appear nicks or spots, which will lose the seal and cause the injector to drip.
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 irregular firing sounds. If the oil supply to the tank is stopped at this time, the smoke exhaust and the sound of the gun will disappear.
Solution: The 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 in the needle valve hole) to grind the cone surface, then wash it with diesel oil and put it into the injector for testing.
If it still fails, you need to replace the needle valve assembly.
Precautions for reducing injector failure
- First, check the injection pressure and sealing of the injector. Secondly, check the atomization quality of the fuel injector, carefully observe the shape, number, oil droplet fineness, and distribution of the spray column, and pay attention to whether there is fuel dripping at the nozzle hole before the valve opening pressure and after the injection. Good atomization quality means that the spray column meets the requirements, and there is no gushing or leakage of oil droplets, and there is a crisp "squeak" during the entire spraying process.
- Before installing the injector into the cylinder. First, check whether the sealing ring on the injector is intact. Then check the cleanliness and tightness of the sealing surface of the fuel injector and the cylinder head, and clean and grind if necessary to prevent gas leakage and burn the fuel injector. At the same time, note that the fastening nut of the injector on the cylinder head should not be over tightened, and must be strictly following the regulations of the instruction manual.
- In the case of meeting the requirements of use, the diesel engine should be kept running under higher load conditions as much as possible, and the combustion quality is the best if the load is above 80%.
- The most suitable fuel should be selected, and the fuel with low sulfur content should be selected as far as possible to ensure the cleanliness of the fuel and reduce the content of impurities and water.