You must understand the most faulty components in the diesel fuel system!

You must understand the most faulty components in the diesel fuel system!

Fuel injector is a key component of diesel engine and one of the components with frequent faults. The occurrence of injector problems is very easy to cause a series of effects on the diesel engine. From the increase of fuel consumption, the reduction of power, and then to the serious wear of parts, it shows that the injector problems have a great impact on the normal operation of the diesel engine.

As we all know, the function of diesel engine injector is to inject diesel into the combustion chamber with fine 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 and works for a long time under the environment of high temperature, high pressure and gas corrosion. The internal moving parts are easily worn and corroded by the impact of high-speed flowing fuel and the repeated scouring of small mechanical impurities in the fuel. It is one of the most faulty parts in the diesel engine fuel system.

What are the common faults of fuel injector? How to check?

The common faults of fuel injector include nozzle hole blockage, needle valve coupling wear, high or low fuel injector pressure, etc. In order to ensure the good power and economy of diesel engine, we should also pay attention to the injection direction and shape of fuel injector. Generally, the fuel injector shall be maintained every 5000km.

If it is suspected that a cylinder of diesel engine does not work and the high-pressure oil pipe feels strong pulsation, the usual practice is to remove the fuel injector for inspection. Before disassembly, check whether the fuel return pipe of the fuel injector is installed. When loosening the fixing bolt, test the torque. When pulling out the fuel injector, pay attention to whether the front end is equipped with a gasket and whether there is a blow by blackening mark on the head, which can help analyze the cause of the fault. For example, not installing the oil return pipe is the factor that impurities enter the injector and cause the needle valve or ejector rod to jam. Insufficient tightening torque is the factor causing poor heat dissipation and air leakage of fuel injector. If you see the blowby blackening mark on the head of the fuel injector, you can confirm that it is the root cause of the blockage.

The injector must be connected to the injector tester for inspection, check the quantity and shape of injection, and compare with the injection of the new injector to judge whether the injection hole is completely or partially blocked.

For the blocked orifice, find out the specific causes. If the valve needle is stuck in the needle valve body, knock it out with an inertia hammer, and pay attention to observe its surface state to see if there are scratches, adhesives, and whether the surface becomes wheat yellow, blue or other colors.

If there are scratches on the surface of the valve needle, it can be considered that the blockage is caused by the needle valve hairpin. If there is no high-speed injection oil flow to clean and cool the spray hole, the high heat gas will sinter the remaining oil in the spray hole in a very short time, resulting in blockage. If there is adhesive on the needle valve, it indicates that the needle valve has intermittent hairpin fault. If the injector is found dripping or stained with oil on the injector tester, it can be considered that the reason for the blockage is that the needle valve and valve seat are not tightly sealed, If the dripping oil is sintered in the spray hole by high heat gas and causes blockage, focus on checking the tightness of the needle valve coupling. If the needle valve has turned blue, it indicates that the heat dissipation of the fuel injector is poor. Focus on checking whether the fuel injector can be in close contact with adjacent parts and can be compressed. If necessary, replace the needle valve coupling.

How to detect the fuel injector?

Most diesel engines use closed fuel injectors. When the fuel injector does not inject fuel, the nozzle hole is closed by the needle valve to separate the combustion chamber from the high-pressure oil circuit. During the operation of the fuel injector, a small amount of fuel will seep out from the small gap between the needle valve and the needle valve body. This part of fuel can lubricate the needle valve, rise along the gap around the ejector rod and flow back to the oil tank through the return pipe.

1. Tightness test. Before the test, check the tightness of the injector tester, and then conduct the tightness test on the cylindrical working surface and conical working surface of the injector needle valve and needle valve body after meeting the requirements. The inspection and test methods and requirements are as follows:

(1) When checking the tightness of the injector tester, first block the high-pressure oil pipe of the injector, then press the handle to make the pressure rise to 29400kpa, observe the pressure drop within 3min, and it is good if it is not greater than 980kpa.

(2) When testing the tightness of the cylindrical working surface of the needle valve and needle valve body, first install the fuel injector on the high-pressure oil outlet pipe of the tester, continuously press the handle, and screw the pressure regulating screw of the fuel injector with a screwdriver to adjust the fuel injection pressure to 22540kpa, and then the time required for the pressure of the measuring plate to drop from 19600kpa to 17640kpa shall not be less than 6 ~ 15s.

(3) Test the tightness of the conical working surface of the needle valve and needle valve body, screw the pressure regulating screw and continuously press the handle, first adjust the injection pressure to the standard injection pressure, then quickly increase the oil pressure to 1960kpa lower than the injection pressure, and evenly increase it to start injection at the speed of 980kpa in 3 ~ 5S. The injection shall be in the form of fog. After the start and end of fuel injection, a small amount of moisture is allowed around the fuel injection hole, but oil droplet condensation is not allowed.

2. Adjustment of injection pressure

(1) Turn the pressure regulating screw, the pressure increases when screwing in, otherwise the pressure decreases, turn the tester handle slowly, and the fuel injector shall start fuel injection when the pressure regulating gauge needle points to 17150kpa.

(2) After adjustment, install the washer and pressure regulating screw locknut, tighten the locknut with a torque of 58.8 ~ 78.4n · m, and then re calibrate the injection pressure until it meets the requirements.

(3) The injection pressure of each injector of the same diesel engine shall be consistent, and the difference shall not exceed 490kpa.

3. Spray test

Operate the handle at the speed of 2 ~ 3 times per second according to the specified injection pressure. The oil mist shall be evenly distributed without oil droplet splashing. When the fuel injection stops, there shall be a clear sound, but after multiple injections, the spray hole is allowed to be wet. If the atomization is poor, replace the fuel injector assembly.

How to check whether the fuel injector is repaired?

Install the repaired fuel injector on the fuel injector tester for fuel injection test and pressure holding test.

(1) Fuel injection test. Conduct pressure adjustment and fuel injection test, check the shape, direction, consistency and fineness of fuel injection column, and observe whether there are oil droplets or oil accumulation at the fuel injection nozzle.

(2) Pressure holding test. When the test diesel oil temperature is 18 ℃ ~ 20 ℃, press the pump oil handle of the tester to make the pressure indication number 30 MPa, and then observe the decline process of the indication number. If the time from 28kpa to 23kpa is less than 8s, and there is no oil drop and oil accumulation at the end of the injector, it indicates that the guide part of the needle valve has leakage, and the needle valve coupling must be replaced. If there is oil drop and oil accumulation at the end of the injector, it indicates that the sealing belt of the needle valve coupling is not sealed, and it should be grinded again or replaced with a new one.