The Common Malfunction of Injector and Its Solution

F-DIESEL FIE SYSTEM 19/2/21 3:57:14 AM

[Key Words] injector

The fuel injector is one of the vulnerable parts of diesel engines. It is prone to malfunction if it works under high temperature and high pressure for a long time. The causes of several common failures of fuel injectors are analyzed, and the prevention and elimination methods are proposed.

The fuel injector is one of the important parts of the diesel engine fuel system, and its main functions are as follows:
1. The fuel injector sprays and atomizes high-pressure fuel;
2. When the fuel injector is injecting, according to the form of the combustion chamber, it forms a jet with a certain injection angle and penetration ability, and forms a good quality combustible mixture with the fresh air in the combustion chamber;
3. The fuel injector must also comply with a certain fuel supply law, and at the same time, the fuel supply should be correct at the beginning, stop fuel decisively, and not drip.

Fuel injectors can be divided into two categories, namely, open and closed injectors. Closed injectors are widely used in diesel engines. The needle valve assembly (nozzle) in the injector is extremely precise, and it works under high temperature and high pressure conditions, which is prone to failure. Some injectors have a short service life, ranging from one year to several months, or even scrapped within three or five days. The user and repairer should know the cause of the failure and pay attention to prevention.

Malfunctions and solutions

The injector needle valve is stuck

When the needle valve is stuck, the injector will not work, and the single-cylinder diesel engine will shut down.

1.1 Causes of failure

(1) Poor heat dissipation from the fuel injector. The main reasons for the poor heat dissipation of the fuel injector are: the copper pad of the fuel injector does not meet the requirements; the adjustment of the fuel supply time is not accurate; the sealing cone of the needle valve is damaged, and the combustible gas in the cylinder flows into the guide surface to form carbon deposits and become stuck. .

(2) Diesel oil is not clean, water or acidic substances make the needle valve rusty.

(3) The needle valve is stuck due to bumps during disassembly, improper cleaning or incorrect installation.

(4) The anti-rust oil is not removed when installing a new fuel injector, and the anti-rust oil will stick to the needle valve after being melted at high temperature.

1.2 Preventive measures

(1) Use qualified fuel injectors instead of substitutes.
(2) The fuel supply advance angle, gas distribution phase and fuel injection pressure must meet the technical requirements.
(3) When disassembling and assembling the fuel injection nozzle, do not touch the needle valve assembly and do not mix. Install the fuel injector assembly, and pay attention to the cleaning of the fuel injector mounting seat hole. When installing the fuel injector fixing bolts, the torque should meet the requirements and tighten them evenly in 3 to 4 times.
(4) When the locomotive is parked for a long time, remove the fuel injector assembly from the engine, plug the mounting hole with a wooden plug, and place it in clean engine oil.
(5) The newly replaced injectors must be boiled in clean diesel at 60～80℃ for 10 minutes to remove the anti-rust oil on them.

2. Carbon deposit in the oil nozzle is blocked

When the carbon deposit in the nozzle hole is half blocked, the fuel injection volume of the fuel injector decreases, the fuel return volume increases, and the diesel engine is weak. When the carbon deposit in the nozzle hole is fully clogged, the malfunction of the diesel engine is the same as the malfunction of the injector needle valve, that is, the injector does not inject and does not work.

2.1 Causes of failure

The main reason for the clogging of the fuel injector with carbon deposits is that diesel and engine oil are not completely burned in the cylinder, and they combine with the dust of the air intake to form carbon deposits. Carbon deposits adhere to the valves, pistons, cylinder liners, exhaust pipes and fuel injectors in the combustion chamber.

2.2 Preventive measures

(1) Ensure that the fresh air in the cylinder of the diesel engine is sufficient and the exhaust gas is exhausted cleanly.
(2) Keep the technical condition of the fuel injector in good condition, the fuel injection pressure should be within the specified range, the atomization should be good, and no oil drips or leaks.
(3) Maintain the normal technical status of the locomotive and prevent the occurrence of engine oil burning.
(4) When operating the tractor, you must control the starting throttle correctly. Do not start the diesel engine forcibly. Do not start the diesel engine multiple times in succession. This will cause too much fuel in the injection cylinder, which will cause difficulty in starting and cause excessive carbon deposits in the cylinder.

3. The lift of the oil nozzle needle valve increases

Increased injector needle valve lift reduces engine power and increases fuel consumption. Some exhaust smoke. Disassemble the injector and check it, and you will find that the sealing surface of the injector body is dented after being hit by the needle valve shoulder.

3.1 Causes of failure

When the diesel engine is working, the injector injects oil several times in a cycle. After long-term impact, the hard injector body sealing surface and the needle valve tail shoulder wear and sink, thereby increasing the needle valve lift.

3.2 Elimination method

(1) The sealing surface of the injector body can be ground with chromium oxide or aluminum oxide on the glass plate. When grinding, the hand must be held flat, and the force should be even, until it is smooth. The sealing surface shall not leak oil during the test.
(2) Replace the injector body.

4. High pressure oil pipe return air

When the diesel engine is running, a certain cylinder does not work normally, and the sound produced is also abnormal. When using the "cylinder-breaking method" to diagnose, after loosening the high-pressure tubing of the cylinder, gas can be found out of the high-pressure tubing.

4.1 Causes of failure

(1) The contact surface between the upper end surface of the needle valve seat body and the injector is not flat, and the gas enters the injector body through the gap of the joint surface, and then to the high-pressure oil pipe.
(2) The injector needle valve is stuck in the open position. When the diesel engine is cycled to the compression stroke, high-pressure gas enters the high-pressure oil pipe through the nozzle hole.

4.2 Elimination method

(1) The end face of the injector needle valve seat body can be ground with chromium oxide or aluminum oxide on the glass plate. Pinch the needle valve body with your hands and place it upside down on the glass plate to grind until it is flat.

(2) After disassembling the needle valve by the method of disassembling it, put a little clean oil on the needle valve and put it in the needle valve body for grinding.

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