Don't miss the 8 reasons for the failure of diesel injectors!
27 Oct 2021
The function of the diesel fuel injector is to inject diesel fuel into the combustion chamber with finer atomized particles to form a good combustible mixture with air.
The fuel injector is installed on the cylinder head. The fuel injector 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 erosion of small mechanical impurities in the fuel. Easily worn and corroded, it is one of the most faulty parts in the diesel engine fuel system.
This article briefly introduces 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 is carbon deposits, the spring end surface is worn or the elastic force drops, it will cause the fuel injector to open in advance and delay to close, 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 machine will not run normally. In addition, because diesel mist droplets with an excessively large particle size cannot be fully burned, they flow into the oil accumulation 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 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 tightly matched, the oil return of the injector will increase significantly, and some can reach 0.1 to 0.3 kg/h. If the 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 oil tank smoothly. 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 fuel injector.
Three needle valve nozzle hole expansion
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 drop in fuel injection pressure, a shortened injection distance, poor diesel atomization, and an increase in carbon deposits in the cylinder.
Solution: The diameter of the single-hole shaft needle injector is generally larger than 1mm. You can put a steel ball with a diameter of 4 to 5 mm at the end of the hole and tap it lightly with a hammer to cause local plastic deformation of the nozzle hole and reduce the hole diameter. . Due to the large number of holes and the small diameter of the multi-hole direct injection injector, it can only be tapped lightly 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.
Four needle valve seized
Moisture or acidic substances 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 flow into the mating surface to form carbon deposits, causing the needle valve to seize and the fuel injector. The fuel injection effect is lost, causing the cylinder to stop working.
Solution: Put the needle valve assembly in the waste engine oil and heat it until it boils and smoke, and then take it out. Use the pliers padded with a soft cloth to clamp the needle valve tail and move it slowly, then pull it out and stain it with clean engine oil. 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 assembly is turned upside down. If the fuel injector fails to pass the test, the needle valve assembly should be replaced.
Fifth, 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 to a grinder to grind the end surface, and then use a fine grinding paste to grind the glass plate.
Sixth, the fuel injector and cylinder head joint hole leaks and blows oil
When installing the cylinder head on the injector, carefully remove the carbon deposits in the mounting hole, and 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 from the injector to the plane of the cylinder head meets the technical requirements. In addition, 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 and oil leakage.
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, resulting in an increase in the gap or scratches, resulting in an increase in the internal leakage of the injector and the pressure Decrease, the amount of fuel injection is reduced, and the fuel injection time lags, 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 fuel injector is working, the sealing cone of the needle valve body will be subject to frequent and strong impacts from the needle valve. Coupled with the continuous injection of high-pressure oil from there, the cone will gradually appear nicks or spots, which will lose the seal and cause The injector is dripping oil.
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 shooting will disappear.
Solution: The fuel injector can be disassembled, and a little chromium oxide fine grinding paste is applied to the needle valve head (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 fuel injector for testing . If it still fails, you need to replace the needle valve assembly.
Precautions to reduce injector failure
1. Inspection of the fuel injector
First, check the opening 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 "squeaking" sound during the entire spraying process.
Two matters needing attention during assembly
Before installing the fuel injector into the cylinder, first check whether the sealing ring on the fuel injector is intact, and 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 , Burn the 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 in accordance with the provisions of the instruction manual.
Three try to keep the diesel engine in good working condition
In the case of meeting the requirements of use, the diesel engine should be kept running under higher load conditions as much as possible. The combustion quality is the best if the load is above 80%.
Four reasonable selection of fuel
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.
The fuel injector is installed on the cylinder head. The fuel injector 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 erosion of small mechanical impurities in the fuel. Easily worn and corroded, it is one of the most faulty parts in the diesel engine fuel system.
This article briefly introduces 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 is carbon deposits, the spring end surface is worn or the elastic force drops, it will cause the fuel injector to open in advance and delay to close, 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 machine will not run normally. In addition, because diesel mist droplets with an excessively large particle size cannot be fully burned, they flow into the oil accumulation 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 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 tightly matched, the oil return of the injector will increase significantly, and some can reach 0.1 to 0.3 kg/h. If the 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 oil tank smoothly. 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 fuel injector.
Three needle valve nozzle hole expansion
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 drop in fuel injection pressure, a shortened injection distance, poor diesel atomization, and an increase in carbon deposits in the cylinder.
Solution: The diameter of the single-hole shaft needle injector is generally larger than 1mm. You can put a steel ball with a diameter of 4 to 5 mm at the end of the hole and tap it lightly with a hammer to cause local plastic deformation of the nozzle hole and reduce the hole diameter. . Due to the large number of holes and the small diameter of the multi-hole direct injection injector, it can only be tapped lightly 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.
Four needle valve seized
Moisture or acidic substances 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 flow into the mating surface to form carbon deposits, causing the needle valve to seize and the fuel injector. The fuel injection effect is lost, causing the cylinder to stop working.
Solution: Put the needle valve assembly in the waste engine oil and heat it until it boils and smoke, and then take it out. Use the pliers padded with a soft cloth to clamp the needle valve tail and move it slowly, then pull it out and stain it with clean engine oil. 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 assembly is turned upside down. If the fuel injector fails to pass the test, the needle valve assembly should be replaced.
Fifth, 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 to a grinder to grind the end surface, and then use a fine grinding paste to grind the glass plate.
Sixth, the fuel injector and cylinder head joint hole leaks and blows oil
When installing the cylinder head on the injector, carefully remove the carbon deposits in the mounting hole, and 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 from the injector to the plane of the cylinder head meets the technical requirements. In addition, 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 and oil leakage.
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, resulting in an increase in the gap or scratches, resulting in an increase in the internal leakage of the injector and the pressure Decrease, the amount of fuel injection is reduced, and the fuel injection time lags, 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 fuel injector is working, the sealing cone of the needle valve body will be subject to frequent and strong impacts from the needle valve. Coupled with the continuous injection of high-pressure oil from there, the cone will gradually appear nicks or spots, which will lose the seal and cause The injector is dripping oil.
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 shooting will disappear.
Solution: The fuel injector can be disassembled, and a little chromium oxide fine grinding paste is applied to the needle valve head (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 fuel injector for testing . If it still fails, you need to replace the needle valve assembly.
Precautions to reduce injector failure
1. Inspection of the fuel injector
First, check the opening 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 "squeaking" sound during the entire spraying process.
Two matters needing attention during assembly
Before installing the fuel injector into the cylinder, first check whether the sealing ring on the fuel injector is intact, and 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 , Burn the 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 in accordance with the provisions of the instruction manual.
Three try to keep the diesel engine in good working condition
In the case of meeting the requirements of use, the diesel engine should be kept running under higher load conditions as much as possible. The combustion quality is the best if the load is above 80%.
Four reasonable selection of fuel
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.
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