The function of the injector is to spray the fuel into finer mist droplets, and according to the requirements of the form of the combustion chamber, the fuel is dispersed in the combustion chamber and mixed with the compressed air to combust. The quality of the injector's work quality has a great impact on the performance of the diesel engine, so in the use of the diesel engine, we must pay attention to the use and maintenance of the injector.
1 Structural characteristics of the injector
The fuel injector is mainly composed of fuel injector body, needle valve coupler, ejector rod, fuel injector spring, tight cap and pressure regulating screw. The high-pressure fuel sent from the injection pump enters the annular cavity of the injector body and the needle valve coupling. When the pressure reaches 11. 77 MPa (ZS4S1 injector), the needle valve is lifted against the pressure of the spring. At this time, a certain amount of fuel is sprayed into the vortex chamber through a spray hole. After the fuel is injected, the pressure drops, and the needle valve blocks the injection hole again under the action of the spring force. The fuel leaked from the gap between the plunger surface of the needle valve assembly rises from the inside of the casing through the pipe joint bolt and the oil return pipe, and part of it is used as the glow plug winter cold start oil, and most of it flows back to the fuel tank.
2 Inspection and disassembly of injector
When the engine suffers from insufficient power or black smoke, the first thing to think about is whether the injector is not working properly. At this time, the injector can be removed from the engine and tested on the injector test bench. 11. Press the handle of the hand oil pump evenly at a speed of 10 times per minute to check the injection pressure and dripping. At 77 MPa, injection starts. Before this time, there must be no leakage in the fuel injection nozzle. A small amount of moisture is allowed in the injection hole, but there must be no oil dripping. If the oil dripping phenomenon indicates that the conical surface is not well sealed, the fuel injection nozzle should be cleaned or the sealed conical surface should be ground. If the injection pressure does not meet the requirements, you can loosen the protective cap to adjust, and increase the injection pressure by screwing in the pressure regulating screw, otherwise the injection pressure decreases.
When the fuel injection pressure meets the requirements, the hand oil pump handle can be pressed at a speed of 60 to 70 times per minute. Observe the spray condition. The oil mist should be fine and uniform, and there should be no splash of oil droplets visible to the naked eye. The cone angle of the mist beam direction is about 4 °. The fuel should be cut off promptly and the sound is crisp. If it does not meet the requirements, it should be dismantled.
When the injector needs to be disassembled and inspected, the disassembled injector should be cleaned in clean kerosene or diesel oil. Rough and fine wash containers should be separated. Needle valve pairs should be placed in pairs and not messy. The dirt can only be scraped off with wood or copper, and then wiped with a soft cloth. Cotton yarn is prohibited. The cleaned needle valve should have good sliding properties. After wetting the needle valve coupler with light diesel, withdraw the needle valve from the valve body by 1/3 and tilt the needle valve body by 45 °. Under the action, it should fall slowly without jamming. If the conical surface of the needle valve and seat is poorly sealed, it can be ground with a 500 # green chromium oxide fine grinding paste. The ground needle valve parts should be carefully cleaned.
Before assembly, all parts should be carefully cleaned. When assembling the fuel injection nozzle, the pressure regulating spring should be in a relaxed state. When tightening the injector fastening nut, be sure to apply proper force. For a needle valve body with a large outer diameter of 17 mm, the torque should be 58.8 to 78.4 N · m; for a large outer diameter of 22 mm, the torque should be 78.4 to 98 N · m. When replacing the fuel injection nozzle, be sure to pay attention to the model. It should not be mistaken for the same size and can be used. For example, the ZS15S15 injector and the ZS4S1 can be swapped, but not replaced. After the fuel injector is reinstalled, the test adjustment must be performed again on the test bench.
3 Precautions during use
(1) Pay attention to the quality of the product when purchasing the injector needle valve assembly. If the quality of the needle valve assembly is too poor, the needle valve assembly is not tightly sealed, and the diesel leaks. When the cylinder is compressed and doing work, the diesel fuel on the surface of the nozzle will burn, which will cause the needle valve to become stuck.
(2) The fitting accuracy of the injector needle valve assembly is extremely high, and the injection hole diameter is very small. Therefore, clean diesel oil of a prescribed brand must be selected in strict accordance with seasonal changes. During storage and filling, pay attention to cleanliness. Do not mix impurities into the fuel. Before use, it must be precipitated and filtered before being added to the fuel tank. The diesel filter should be maintained on time, and the sedimentary oil in the filter and the fuel tank is often discharged to prevent the intrusion of dust and dirt and aggravate the wear of the needle valve coupler.
(3) Clean the anti-rust oil for the newly replaced needle valve coupler. The new fuel injector fittings should be cooked in diesel at 70 ～ 80 ℃ for 10 minutes, and then the needle valve should be pulled back and forth in the valve body in clean diesel to thoroughly clean the anti-rust oil. If you only wash without boiling, you will not be able to completely clean the rust preventive oil in the injector parts, and it is easy to cause the needle valve to deposit carbon, cement or even get stuck during work. In addition, when cleaning the needle valve coupling, do not touch it with other hard objects to prevent scratching the needle valve guide surface.
(4) Be careful not to overheat the diesel engine when using it. When the temperature of the diesel engine is too high, the fuel injection nozzle will be deformed by heat and work abnormally. Carbon deposits in the injection holes and the shaft needle will easily cause the needle valve to overheat and die.
(5) Check the fuel injection pressure. Modern diesel engines require different fuel injection pressures due to different combustion chamber structures. The fuel injection pressure of 295 diesel engines is 11. 77 MPa, the fuel injection pressure of the injector is too high or too low to harm the diesel engine. In the initial stage of use of the injector, due to the wear of the parts and the elasticity of the pressure spring, the injection pressure of the injector changes greatly. Excessive fuel injection pressure will increase the amount of dripping and cause carbon deposits. It will also cause the needle valve to get stuck in the closed position of the needle valve body, causing individual cylinders to malfunction or not work. The fuel injection pressure is too high, and the fuel atomization is finer, but the fuel injection distance is too large, causing part of the fuel to be injected into the combustion chamber wall, which is poorly mixed with the air, so that it cannot be completely burned, and also makes the cylinder knock when the diesel engine is running. The fuel injection pressure is too low, the fuel is poorly atomized, the oil mist particles become coarse, and the range is shortened. It cannot penetrate the entire combustion chamber, making the fuel and air poorly mixed, resulting in incomplete combustion of the fuel, exhaust smoke, and increased carbon deposits in the cylinder. Diesel engines are not easy to start. Therefore, in use, the fuel injection pressure and atomization quality of the injector should be checked and adjusted in time. If necessary, it should be adjusted on the injector tester to make the fuel injection pressure and atomization cone angle meet the requirements of the original machine.
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