This article describes the main technical parameters of the fuel injection pump, fuel supply timing, fuel supply amount, fuel supply uniformity, fuel supply pressure, and fuel supply law, and analyzes the influencing factors to improve people’s understanding of the fuel injection pump and reduce The incidence of fuel injection pump failure.
The work task of the fuel injection pump is to supply the fuel injector with the pressure of the low-pressure fuel evenly, quantitatively and evenly. Fuel supply time, fuel supply quantity, fuel supply uniformity, fuel supply pressure, and fuel supply rules are the main technical parameters of the fuel injection pump. If these parameters do not meet the standard requirements, it will affect the normal operation of the diesel engine. Many failures of diesel engines are caused by fuel injection pumps not working properly, and fuel injection pumps are not working properly, mainly due to inaccurate fuel supply timing, uneven fuel supply, incorrect fuel supply pressure, and incorrect fuel supply rules.
(1) Fuel supply and uniformity
Fuel supply refers to the amount of fuel supplied by the fuel injection pump to the fuel injector according to the requirements of the engine’s working load. For multi-cylinder engines, the fuel supply of each cylinder must not differ by 3% to avoid affecting the normal operation of the diesel engine. The fuel supply is controlled by the governor. The governor can automatically change the fuel supply with the load change within the specified speed range, control the maximum speed of the crankshaft and maintain the minimum speed, so that the diesel engine can work normally. The fuel supply of the fuel injection pump is too large, too small and uneven fuel supply will affect the operation of the diesel engine.
If the fuel supply of the fuel injection pump is too small, it will make the diesel engine difficult to start and lack power.
The reason: (1) The fuel supply of the fuel injection pump is adjusted by the fuel volume adjustment mechanism according to the diesel engine load. If the fuel injection control rod and the guide groove of the fuel injection pump are stuck at the position where the fuel supply is at a minimum, or the lever, rack, and fork of the governor are stuck and stuck at the minimum position of the fuel supply, the fuel injection The oil supply of the oil pump is too small.
(2) The plunger assembly of the fuel injection pump is severely worn, and the sealing performance is reduced, which will also cause a decrease in fuel supply pressure and fuel supply amount.
(3) The fuel injection pump outlet valve coupler works poorly, and the internal leakage increases, causing the fuel supply to decrease.
If the fuel supply of the fuel injection pump is too large, black smoke will appear due to the abnormal air-fuel ratio.
The reason: (1) Improper adjustment of plunger makes the fuel supply too large.
(2) The lock nut of the adjustment gear is loosened, and the adjustment gear is displaced.
(3) The governor’s control arm limit screw is improperly adjusted. In order to increase the speed of the locomotive, some pilots abnormally adjust the speed adjustment screw and the oil limiter; even more, the throttle lever is directly hung on the speed spring to increase the speed erroneously, which not only accelerates the wear of the parts, The safety of the locomotive will also be reduced; the mechanical efficiency will decrease and the fuel consumption rate will increase. According to the measurement, the fuel consumption rate will increase by 3% to 4% when the speed exceeds 10% of the specified limit value.
The uneven fuel supply of the multi-cylinder diesel engine will cause the cylinder with a large amount of oil to knock and emit black smoke when working. At idle speed, there will be a “touring” phenomenon when the speed fluctuation is severe. The reason: improper fuel injection pump calibration, wear of the maximum fuel supply restriction device, improper assembly or adjustment of the fuel quantity control mechanism, etc. In addition, the main parts of the fuel injection pump and fuel injector of each cylinder are unevenly worn, or the plunger spring and oil outlet valve The spring is permanently deformed or broken.
2 Fuel supply time
According to the requirements of the engine, the fuel injection pump should accurately supply fuel to the cylinder at the specified time, and the fuel supply advance angle of each cylinder (the crank angle corresponding to the crankshaft corresponding to the top dead center of the fuel injection pump) should be consistent. In addition to the original fuel supply advance angle, the vehicle diesel engine also requires that the fuel advance angle can change with the speed (automatic fuel supply advance angle adjustment device). In order to ensure the working performance of the diesel engine, the fuel injection pump is also required to have a certain fuel supply to continue between the pairs. The fuel supply advance angle is specified at the factory. If the fuel supply is too early (the advance angle is too large), the diesel is injected at low air temperature and pressure in the cylinder. It is difficult to start, it is easy to reverse when starting, the fuel consumption rate increases and the power decreases. If the fuel supply is too late (the advance angle is too small), the diesel combustion process will continue after the top dead center, which will make the combustion incomplete, the exhaust smoke, the engine temperature is too high, it is also difficult to start, the fuel consumption rate increases, the power decline. Such as 190A diesel engine fuel supply advance angle is reduced from 39 ° to 30 °, 9S195 model is reduced from 18 ° to 13 °, the power drops by about 1.5 kW and 1.8 kW. Therefore, in the technical diagnosis of the fuel system, whether the detection and adjustment of the fuel supply advance angle are correct or not plays an important role in restoring the power performance and economic performance of the diesel engine.
The main reasons affecting the fuel supply advance angle: First, the wear of various transmission parts, such as the oil pump cam, rollers, pads, plunger end wear, and plunger pair wear, etc; Second, improper adjustment of the gasket, the gasket is not extracted in time, or No suitable shim can be used for adjustment; third, some operators have poor technical skills and will not adjust or dare to adjust.
3 Fuel supply pressure
The fuel supplied by the fuel injection pump to the fuel injector must have a certain pressure to ensure that the fuel can be atomized well in the fuel injector. The injection pressure is too low, the atomization is poor, and the diesel engine is difficult to start; the fuel consumption rate increases, the exhaust emits black smoke, and the lower end of the needle valve body is easy to deposit carbon. The fuel injection pressure is too high, which accelerates the wear of the fuel injection pump and fuel injector parts, and sometimes ruptures the high-pressure fuel pipe. Excessive deviation of injection pressure will inevitably reduce the power of the diesel engine and increase the fuel consumption rate.
The main reason for the lack of fuel supply pressure is: after the injection pump plunger coupler and the oil outlet valve coupler wear out, the sealing performance decreases, resulting in a decrease in fuel injection pressure, causing poor atomization. The reason for the high and low fuel injection pressure is also due to artificial adjustment: if some maintenance personnel do not use the instrument for testing, but adjust the injection pressure based on experience; if some maintenance personnel observe the spray quality to judge the injection pressure; some Judge the fuel injection pressure by listening to the sound of fuel injection; some pilots point their hands at the fuel injectors and spray fuel onto their hands, judging by the palm feeling. These experiences vary from person to person and are quite different, and the transferred fuel supply pressure is not accurate. Some pilots also intend to increase the fuel injection pressure, thinking that this can use high-pressure fuel to wash away the carbon deposits in the fuel injector, and can also make up for eliminating the fuel injector fuel drop phenomenon.
4 Fuel supply law
The fuel injection pump should supply fuel to the fuel injector according to a reasonable fuel supply law to ensure that the fuel injection law of the fuel injector cooperates well with the formation of the mixed gas and the combustion process. In addition, in order to prevent the drip phenomenon of the fuel injector, the fuel injection pump must also ensure that the fuel supply can be stopped quickly.
The fuel supply law of the fuel injection pump is determined by the shape of the cam profile and the movement of the plunger. At different positions, the fuel supply law is different. However, the shape of the cam cannot be changed by the design, but the position of the starting point of the fuel supply can be Adjusted. If the fuel supply duration of the plunger is within the incorrect range of the cam profile, it will slow the start of fuel supply, cause the fuel supply duration to be too long and cause a backward movement, and increase the thermal load of diesel engine parts.