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At the end of the compression stroke of the diesel engine, the pressure in the cylinder reaches 3 to 5 Mpa and the temperature is 500 to 700°C. To make the diesel enter the cylinder under this condition, the injection pressure should be higher than 12.5 MPa and the injection speed should be greater than 100 m/s. Fuel injection pumps and injectors are used to accomplish this task. The fuel injection pump is used to generate high pressure in the diesel fuel and is periodically delivered to the injector. The fuel injector atomizes the diesel fuel from the fuel injection pump and evenly distributes it to the combustion chambers of each cylinder so that it can be fully burned.
The injector is a key part of the diesel engine. Its material is good and the manufacturing process is fine. If the fuel injection pump is normal and the injector is not working properly, the diesel fuel cannot be completely burned. As a result, the fuel consumption of the diesel engine increases, the power drops, the carbon deposit in the cylinder increases, and the wear of the engine parts increases. Therefore, in the use and maintenance of the vehicle, the injector must be highly valued.
1 Types of Injectors The diesel engine used on tractors is a high-speed diesel engine with a rotational speed greater than 1000 r/min. The injectors are generally available in two types: pintle and perforated. The shaft pin type is mainly used for vortex or pre-combustion combustion chambers and is reliable in operation. Because there is only one orifice and the pore size is large, it is not easy to be blocked by carbon deposition, but its thermal efficiency is low and the fuel consumption rate is high. The porous type is mainly used in direct-injection combustion chambers, which can simultaneously eject several spray cones with small cone angles and long range, and thus the required injection pressure is also much larger than the pin type. This type of injector has high thermal efficiency and fuel economy, but it has strict requirements on the grade, quality, and cleanliness of the oil, otherwise the diesel engine will not operate normally. For example, in the 135 series diesel engine, the injector has 4 injection holes with an aperture of 0.35 mm.
2 Injector Common Faults The most precise needle valve and needle body in the injector has a clearance of 0.002 to 0.004 mm. If dirt impurities in the diesel, it will affect the sensitivity of the needle valve opening and closing, and even stuck. Because the injector head is in direct contact with the high-temperature and high-pressure gas in the combustion chamber, the needle valve will swell, deform, or be blocked by the carbon deposition due to the long time, thereby reducing the quality of the injection and affecting the normal operation of the diesel engine. The common faults and exclusion methods of injectors are described below.
2.1 Injector drip oil When the injector is working, the sealing cone surface of the needle valve body will be subject to the frequent strong impact of the needle valve, and the high pressure oil flow will be continuously ejected from this place. The taper surface will gradually be nicked or spotted. , Which loses the seal and causes the injector to drip. When the temperature of the diesel engine is low, the exhaust pipe emits white smoke, and when the temperature of the engine increases, it becomes black smoke, and the exhaust pipe emits an irregular sound of a shot. If oil supply to the cylinder is stopped at this time, the smoke emission and blasting will disappear. At this time, the fuel injector can be disassembled, and a small amount of chromium oxide fine paste (not to be stuck in the needle valve hole) is ground on the needle head, then the cone is ground, then washed with diesel oil, and put into the injector test. If it still fails, replace the needle valve assembly.
2.2 Insufficient atomization of fuel injector When the fuel injection pressure is too low, there is carbon deposition in the nozzle hole, and when the spring end surface wears or the elastic force drops, the injector will be opened in advance, the delay will be turned off, and the phenomenon of poor fuel atomization will be formed. If the single-cylinder diesel engine can not work, the multi-cylinder diesel engine will decrease in power, the exhaust will emit black smoke, and the machine operation sound will be abnormal. In addition, because the diesel droplets with too large particle size cannot be fully burned, they will flow into the oil pan along the cylinder wall, increasing the oil level of the oil, lowering the viscosity, and deteriorating the lubrication. This may also lead to accidents of burning the cylinder. At this point, the injector should be disassembled and cleaned, overhauled, and recommissioned.
2.3 Spray hole expansion As the high-pressure oil flow continues to be flushed, the needle valve orifice will gradually wear out, resulting in lower injection pressure, shorter injection distance, poor diesel atomization, and an increase in the amount of carbon deposit in the cylinder. The hole diameter of a single-hole pin injector is generally larger than 1 mm. A steel ball with a diameter of 4 to 5 mm can be placed at the hole end, and tapped with a hammer to make plastic deformation of the injection hole to narrow the hole diameter. Due to the large number of holes and small aperture, the multi-hole direct injection injector can only be tapped on the end of the hole with high-speed steel grinding. If it fails to pass the adjustment, the needle valve coupler should be replaced.
2.4 Pinching the moisture or acid in the diesel needle will cause the needle valve to rust and become stuck. After the conical surface of the needle valve is damaged, the combustible gas in the cylinder will also enter the mating surface to form carbon deposits, making the needle valve bite. When it is dead, the injector loses fuel injection, causing the cylinder to stop working. The needle valve can be placed in the waste oil and heated until boiling smoke. Then remove it, clamp the needle valve with a soft cloth and slowly move the tail of the needle valve. Pull it out to clean the engine oil and let the needle valve The inside of the valve body is repeatedly ground until the needle valve can slowly withdraw from the valve body when the needle valve is turned upside down. If the injector test fails, replace the needle valve assembly.
2.5 Needle Body Wear on the End Surface of the needle body is subject to frequent reciprocating motions of the needle valve. As time passes, the dents will gradually form, increasing the lift of the needle valve 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 abrasive paste on a glass plate.
2.6 needle valve and needle valve hole guide surface wear needle valve in the needle valve hole frequently reciprocating movement, coupled with the intrusion of impurities in the diesel fuel will make the needle valve hole guide surface gradually wear, so the gap increases or there is a nick As a result, the internal leakage of the injector increases, the pressure decreases, the injection amount decreases, and the injection time lags behind, resulting in difficulty in starting the diesel engine. When the delay of fuel injection time is too long, the locomotive cannot even operate, and the needle valves should be replaced at this time.
2.7 Leakage of fuel injector and cylinder head leakage oil When the injector is installed with the cylinder head, the carbon deposit in the installation hole should be carefully removed. The copper gasket must be flat and must not be replaced with an asbestos plate or other materials to prevent poor heat dissipation. Or do not seal. 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. For example, the distance of the 135 series diesel engine is 1.5 to 2 mm, and too large and small will affect the cylinder compression ratio. In addition, the concave shape of the fuel injector pressure plate should be installed downwards. Avoid unilateral bias when tightening. Tighten evenly according to the specified torque. Otherwise, the injector head will deform due to deflection and cause air leakage.
2.8 Damage to the injector return pipe When the needle valve wear is severe or the needle valve body and the injector housing are not tight enough, the oil return of the injector will increase significantly. Some may reach 0.1-0.3 kg/h. . If the return pipe is damaged or missing, the return oil will be wasted, causing waste. 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.
3 Injector maintenance and repair Injector operation should be checked and adjusted once every 700 h. If the opening pressure is lower than the specified value 1 Mpa or more, or if the carbon deposition on the head of the needle valve is serious, the needle valve shall be unloaded and put into the clean diesel fuel to scrape the carbon deposit with wood chips. The fine steel wire shall be used to clear the spray hole and be installed for debugging. It is required that the pressure difference between the cylinders of the same machine must be less than 1 Mpa. Then the oil seal test was conducted, ie, the injection pressure reached 18 MPa, allowing it to drop to 17 MPa on its own, and its return time was not less than 10 s. No diesel oil flowed down the cone or wetted the injector head during the test. In addition, the sprayed oil must be misty and accompanied by a crisp squeak, and each hole in the multi-hole injector should be self-contained. The cone angle of various types of injectors can be compared with a standard injector.
In order to allow the fuel injected into the cylinder of the injector to be fully burned in time, the oil pump's fuel supply time must be checked regularly. If the oil supply time is too early, the vehicle will have difficulty in starting and knocking on the cylinder; if the oil supply time is too late, black smoke will be emitted from the exhaust, the engine temperature will be too high, and the fuel consumption will increase.
The fitting precision of the injector needle valve is very high, and the orifice diameter of the nozzle is very small. Therefore, the clean diesel fuel of the specified grade must be selected strictly in accordance with the season change, otherwise the injector will not work normally. When refueling, prevent rain or snow from mixing and avoid refueling in a dusty environment. To maintain the diesel filter on time, the filter and the precipitated oil in the tank are often drained to prevent ingress of lime sand impurities and to aggravate the wear of the needle valve coupling.
Do not collide with other hard objects while cleaning the needle valve, nor can it fall to the ground to avoid scratches and scratches. When replacing the needle valve parts, the new parts should be soaked in hot diesel oil at 80°C for about 10 s. After the anti-rust oil is completely melted, the needle valve is twitched in the valve body in the clean diesel and thoroughly washed. Net, so as to avoid the failure of the needle valve sticking due to the melting of anti-rust oil when the injector is working. Needle valves must be replaced in pairs and not interchangeable.
If you loosen the high-pressure pipe connector, see a lot of air bubbles or oil bubbles, indicating that the needle valve has been stuck in the open state, so the compressed gas generated when the cylinder is compressed will flow back to the high-pressure fuel pipe through the injector. At this point, the high-pressure fuel pipe is touched by hand. If no pulsation is detected or the pulsation is weak, it indicates that the needle valve has been stuck. The needle valve component should be unloaded to perform grinding and debugging. After commissioning, the new product should be replaced. .
4 Injector maintenance should pay attention to the problem Need to maintain the injector because it is difficult to remove when stuck on the cylinder head, the diesel engine can be decompressed, and crankshaft crankshaft, until the speed increases, immediately put down the pressure rod The cylinder pressure will be used to flush out the injector, but it should be noted that the next station can not stand in order to avoid accidents.
The injector can also be checked in the car. The three-way joint can be used to connect the fuel injector to the standard fuel injector in parallel to the fuel injection pump. At the same time, remove the other high-pressure cylinders, crank the crankshaft or turn the engine with the starter to observe the fuel injection. If two injectors are injected at the same time, the injection pressure is normal; if the injector is injected first, the injection pressure is too low, otherwise it is too high. This can be adjusted individually by screwing in or unscrewing pressure adjusting plugs at the rear of the injector.
The diesel engine cannot be operated at idle speed for a long time to prevent the diesel injector from working poorly due to poor atomization of the diesel fuel. The vehicle must not be overloaded for long periods of time to prevent overheating of the body and causing the injector needle valve to jam. For locomotives stored for a long period of time, the injectors should be removed and cleaned by immersing them in clean diesel oil to prevent the needle valves from rusting and becoming unusable.
In short, in the maintenance, replacement, maintenance work must strictly implement the maintenance process standards, do a good job in the daily inspection, a protection work injector adjustments, maintenance. Only in this way can the service life of the injector be extended.