The Ideas and Methods to Eliminate Common Faults of Diesel Engine Common Rail Injectors

Common-rail injectors are precision-coupled parts of diesel engine systems. The working conditions of fuel injectors directly affect the dynamics, economy, and reliability of diesel engines. It is not difficult to see that the injectors work under the operating principle of injectors. The work needs to have a certain injection pressure, injection stroke, and a suitable injection cone angle. In addition, the injector should be able to quickly cut off the fuel supply when it is necessary to stop the injection, and no drip phenomenon occurs.

During the working process of the injector, there will be various kinds of faults and phenomena. What are the ideas and methods for troubleshooting common injectors? Let us learn together:

Nozzle blockage

Because the fuel is mixed with solid impurity particles, or carbon deposition due to poor combustion, the working time is a little longer and it will accumulate around the nozzle of the injector, so that the nozzle becomes a semi-blocking state. Once the orifice is blocked, the fuel supply pressure of the injection pump will rise and be accompanied by the sound of a knock.

Prevention methods: On the one hand, the fuel that enters the injector must be strictly filtered; on the other hand, by improving the combustion, it can prevent the clogging of the nozzle hole due to excess carbon deposition.

2. Injector drop

When the injector works, the sealing cone surface of the needle valve body will be frequently subjected to strong impact by the needle valve. In addition, high-pressure fuel will be continuously ejected from there, and the cone surface will gradually wear or spot, thereby causing the injector to drip oil. . When the temperature of the diesel engine is low, the exhaust pipe emits white smoke, and when the temperature of the diesel engine rises, it becomes black smoke. The exhaust pipe emits irregular sound, and if the fuel supply to the cylinder is stopped at this time, the smoke emission and sound will disappear.

Remedy: Remove the fuel injector, check the movement of the needle valve is flexible, the sealing of the seat surface is good, and then carefully clean and refit or replace the new nozzle assembly.

3 nozzle corrosion and carbon deposition

The nozzle corrosion is caused by the cold corrosion caused by the sulphide in the exhaust gas. The corrosion nozzle is because the metal surface is so cold that it is subject to chemical attack. Any nozzles that are found to be corroded should be replaced.

The carbon deposit at the end of the nozzle is easily formed when the diesel engine is running at idle speed or under low load. When the load of the diesel engine increases, the carbon residue accumulated on the nozzle will be burned when the fuel is discharged. The carbon deposit at the end has a certain influence on the atomization of the fuel and the uniformity of the fuel distribution in the combustion, resulting in incomplete combustion, a decrease in the power of the diesel engine, and a post-combustion phenomenon and various mechanical failures.

Remedy: Remove the nozzle and remove carbon deposits from the nozzle with mechanical or weak corrosion. The carbon deposition inside the nozzle is very important, but the sealing seat must be protected from damage. In order to prevent the clearing wire from peaking in the hole, the wire must be installed in the collet. The length of the wire exposing the spray hole should not exceed 2 mm.

4. The needle valve stuck

The moisture or acid in diesel oil will cause the needle valve to rust and get stuck. After the conical surface of the needle valve is damaged, the combustible gas in the cylinder will invade into the mating surface to form carbon deposits, which will cause the needle valve to seize the fuel injector. Loss of fuel injection causes the cylinder to stop working.

Remedy: Remove the injector, remove the nozzle assembly, use the tool to pull out the needle valve. If it is not easy to pull out, you can first put the fuel injector into the diesel heating about 20 minutes and then take it. Take a copper pad on the tail of the needle valve, and pull the pliers to grip the tail while rotating. Remove it, place it in the cleaning solution, clean it, and reload it. If it is dirt intrusion, it will be flexible after cleaning. If it is due to the flexible geometry of the coupling, it is necessary to add a small amount of grinding paste, gently polish it, and polish it.

5. Poor atomization of injector

When the injection pressure is too low, the nozzle hole wears carbon, the spring face wears or the elastic force drops. This will cause the injector to open in advance, delay closing, and cause poor atomization of the fuel injection. The power of the diesel engine was reduced, the exhaust gas was black smoke, and the machine operation sound was not normal. In addition, because the diesel droplets with too large particle size do not fully burn, they flow down the cylinder wall into the oil pan, which increases the oil level of the oil, lowers the viscosity, deteriorates the lupication, and may cause an accident of burning the cylinder. At this point, the injector should be disassembled, cleaned, overhauled, and recommissioned.

6. Spring peak

In spite of the permanent deformation caused by the drop of the steel rigidity of the pressure regulating spring of the injector, the peakage often occurs, which has become one of the weak links of the injector. This is mainly due to the poor fatigue resistance of spring steel under high-temperature, high-load, high-frequency operating conditions.

Solution: Improve fatigue resistance, select high-quality heat-resistant and fatigue-resistant materials, and perform surface treatment shot-peening with enhanced fatigue resistance. In order to make the pressure regulating spring work safe and reliable. To reduce the spring power load, the injector can be designed so that the spring can be immersed in the diesel oil in the injector body. When the injector is working, the spring's working ring can generate hydraulic “buffer” and some lupication when in contact. In order to prevent the contact surface from forming a pockmarked surface, the spring peaks.

7. Needle body wear

The needle valve body face is subjected to frequent reciprocating motions of the needle valve, and a pit is gradually formed over time, thereby increasing the needle valve lift and affecting the normal operation of the injector. The needle body can be grinded on a grinding bed to grind this end surface and then ground with a fine apasive paste on a glass plate.

8. Needle valve and needle valve hole guide surface wear

The needle valve frequently reciprocates in the needle valve hole, and the intrusion of impurities in the diesel oil will gradually wear the guide surface of the needle valve hole. As a result, the clearance increases or a nick is formed, which leads to an increase in the internal leakage of the injector. Reduced, reduced fuel injection, delayed injection time, resulting in diesel engine start difficult. When the delay of fuel injection time is too much, the diesel engine cannot even operate, and the needle valve coupler should be replaced at this time.

9. Injector and cylinder head coupling hole leakage oil

When the fuel injector is installed with the cylinder head, the carbon deposit in the mounting hole should be carefully removed. The copper gasket must be flat and must not be replaced with an asbestos plate or other material to prevent poor heat dissipation or no sealing effect. If self-made copper washers are used, the copper must be machined to a specified thickness to ensure that the distance from the injector to the plane of the cylinder head meets the technical requirements. In addition, the injector pressure plate should not be unilaterally biased when it is installed in a firm manner. Torque should be tightened evenly according to the regulations, otherwise the injector head will be leaky due to deflection.

10. Injector return pipe poken

When the needle valve coupler wears badly or the needle valve body and the injector housing do not fit tightly enough, the oil return amount of the injector increases obviously, and some can reach 0.1-0.3 kg/h. If the return pipe is damaged or missing, return oil will be lost and waste will result. Therefore, the return pipe must be intact and sealed so that the return oil can smoothly flow into the tank. If the return pipe is connected to a diesel filter, a one-way valve shall be provided at the terminal to prevent diesel oil in the filter from flowing back into the injector.