Common Trouble shooting Ideas and Methods of Common Rail Injector for Diesel Engine

Writer：admin Date：2024-09-05 Click：903

The common rail injector is a precision coupling part of the diesel engine system. The working condition of the injector directly affects the power, economy and reliability of the diesel engine. It is not difficult to see from the working principle of the injector. The work needs to have a certain injection pressure, injection stroke, and appropriate injection cone angle. In addition, the injector should be able to quickly cut off the fuel supply when it needs to stop fuel injection without dripping.
In the working process of the injector, there will be a variety of faults and phenomena, so what are the common troubleshooting ideas and methods of the injector:
　

1. The nozzle is blocked
Because the fuel is mixed with solid impurity particles, or carbon deposits due to poor combustion, it will accumulate around the nozzle hole of the injector after a long working time, making the nozzle hole semi-blocked. Once the nozzle is blocked, the fuel supply pressure of the fuel injection pump will rise and be accompanied by a knocking sound.
Prevention method: On the one hand, the fuel entering the fuel injector must be strictly filtered; on the other hand, by improving combustion, it can prevent the nozzle from being blocked due to excessive carbon deposits.

2. Oil dripping from the nozzle
When the fuel injector is working, the sealing cone of the needle valve body will be frequently impacted by the needle valve, and the high-pressure fuel will be continuously sprayed from there, and the cone will gradually wear or spots, causing the injector Dripping oil. When the temperature of the diesel engine is low, the exhaust pipe emits white smoke, and the temperature of the diesel engine rises and becomes black smoke. The exhaust pipe will emit irregular firing sounds. At this time, if the fuel supply to the cylinder is stopped, the smoke exhaust and firing sounds will disappear.
Elimination method: Remove the fuel injector, check whether the movement of the needle valve is flexible, and whether the sealing of the seat surface
　

3. Nozzle corrosion and end carbon deposition

The corrosion of the fuel injection nozzle is caused by the cold corrosion caused by the sulfide in the exhaust gas. The corroded nozzle is because the metal surface is too cold to be chemically attacked. Any nozzle found to be corroded shall be replaced.

The carbon deposits at the end of the nozzle are easy to form when the diesel engine is running at idle speed or under low load. When the diesel engine load increases, the carbon residue accumulated on the fuel injector will be burned when the fuel is sprayed. Carbon deposits at the end have a certain impact on the atomization of fuel and the uniformity of fuel distribution during combustion, resulting in incomplete combustion, a decrease in the power of the diesel engine, and an afterburning phenomenon and various mechanical failures.

Exclusion method: remove the nozzle and remove the carbon deposits on the nozzle by mechanical or weak corrosion. The removal of carbon deposits inside the nozzle hole is very important, but it must protect the sealing seat surface from damage. In order to prevent the wire used for cleaning from breaking in the hole, the wire must be installed in the chuck, and the length of the wire exposed from the nozzle hole should not exceed 2mm.

4. The needle valve is stuck

The moisture or acidic substances in the diesel will cause the needle valve to rust and be stuck. After the needle valve sealing cone is damaged, the combustible gas in the cylinder will also escape into the mating surface to form carbon deposits, causing the needle valve to seize and the injector The fuel injection effect is lost, causing the cylinder to stop working.

Elimination method: Remove the fuel injector, take out the fuel injector assembly, and use a tool to pull out the needle valve. If it is not easy to pull out, you can first put the fuel injector assembly in diesel and heat it for about 20 minutes before taking it. When taking, pad copper skin on the tail of the needle valve, clamp the tail with pliers and pull it out while rotating. Pull it out and put it in the cleaning solution for cleaning, then reinstall it. If it is dirt intrusion, it will be flexible after cleaning. If it is due to the geometry of the even piece that affects the flexibility, a small amount of grinding paste should be added for gentle grinding and cleaning after grinding.

5. Poor atomization of fuel injector

When the fuel injection pressure is too low, the nozzle hole is worn with carbon deposits, the spring end face is worn or the elastic force drops, it will cause the fuel injector to open in advance, delay closing, and cause poor fuel injection atomization. The power of the diesel engine drops, the exhaust emits black smoke, and the running sound of the machine is not normal. In addition, because the diesel 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, reduces the viscosity, deteriorates the lubrication, and may also cause accidents of burning and pulling the cylinder. At this time, the injector should be disassembled, cleaned, overhauled and re-debugged.

6. Spring broken

In addition to the permanent deformation of the pressure regulating spring of the injector, the breakage is also frequent, which has become one of the weak links of the injector. Mainly because of the high temperature, high load, high frequency working conditions, spring steel resistance to fatigue strength is poor.

Solution:Improve the fatigue resistance,use high quality heat-resistant fatigue-resistant materialsand carry out surface treatment shot peening to enhance the fatigue resistance. In order to make the pressure regulating spring work safe and reliable. To reduce the power load of the spring, the fuel injector can be designed so that the spring can be immersed in the diesel in the fuel injector body, so that when the fuel injector is working, the working ring of the spring can produce hydraulic "buffer" and certain lubrication effects. To prevent the formation of pitting on the contact surface and cause the spring to break.

7. The end face of the needle valve body is worn

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. The needle valve body can be clamped to the grinding machine to grind this end face, and then use fine grinding paste to grind on the glass plate.

8. Needle valve and needle valve hole guide surface wear

The needle valve frequently reciprocates in the needle valve hole, coupled with the intrusion of impurity pollution in the diesel, the guide surface of the needle valve hole will gradually wear out, so the gap will increase or strain scratches will appear, resulting in increased internal leakage and pressure reduction of the injector, The fuel injection volume is reduced, and the fuel injection time is delayed, which makes it difficult to start the diesel engine. When the fuel injection time delay is too much, the diesel engine can not even run, at this time should replace the needle valve assembly.

9. The combined hole of the fuel injector and the cylinder head leaks and oil channeling

When installing the cylinder head of the injector, the carbon deposit in the installation hole should be carefully removed. The copper gasket must be flat and must not be replaced by asbestos board or other materials to prevent poor heat dissipation or failure to seal. If the self-made copper gasket, it must be processed with copper according to the specified thickness to ensure that the distance from the injector to the cylinder head plane meets the technical requirements. In addition, when the fuel injector pressure plate is installed firmly, avoid unilateral bias, and tighten it evenly according to the specified torque, otherwise the fuel injector head will be deformed and deflected to cause air leakage and oil leakage.

10. The fuel injector return pipe is damaged.

When the needle valve assembly is severely worn or the needle valve body and the injector shell are not tightly matched, the oil return volume of the injector will increase significantly, and some can reach 0.1-0.3 kg/h. If the oil return pipe is damaged or missing, the oil return will be lost, resulting in waste. Therefore, the return pipe must be intact and installed tightly so that the return oil can flow smoothly into the fuel tank. If the 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.

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