Four Major Fault Types Of Diesel Generator Fuel Injection System

The main reasons for the failure of the fuel supply system of the diesel generator mechanical fuel injection pump are:

The three pairs of precision parts are worn out. The failure of the diesel engine fuel supply system mainly occurs in the three pairs of precision parts in the high-pressure oil circuit system (ie plunger and parts, oil outlet parts, needle valve parts of the injector), and the three pairs of precision parts. It is a key component of the entire fuel supply system, and its performance directly affects the working performance of the entire diesel generator.

1. Plunger and coupler: The plunger and coupler are generally ground and selected, so their accuracy is very high, the roughness is very small, and the clearance between the two is very small. When the plunger is in reciprocating motion, it is worn out due to the high-speed, high-pressure and mechanical impurities of diesel scouring. After the piston assembly is worn, the gap between the plunger and the sleeve increases, which leads to an increase in oil leakage, thereby changing the oil supply law. Studies have shown that in the process of starting and final injection, the duration of fuel injection is prolonged, the fuel injection time is prolonged, and the fuel injection time is prolonged, causing the diesel generator to emit black smoke when idling, even under low load. In addition, due to the leakage of the plunger fuel supply, the fuel supply is insufficient, the injection pressure drops, and the power of the diesel generator drops. Because the injection pressure is reduced, it will also make the injectors easy to deposit carbon and jam.

2. Outlet valve assembly: The accuracy of the outlet valve assembly is very high, and its wear position is on the sealing cone of the outlet valve. The reason is that when the delivery valve is depressurized, the reflection of the delivery valve spring and the high-pressure oil pressure wave in the high-pressure oil circuit and the residual pressure make the valve core hit the sealing cone of the valve seat and the impurities in the diesel. After the sealing cone of the outlet valve is worn, the sealing effect will be lost, which will cause irregular backward leakage of the high-pressure oil pipe, reduce the residual pressure of the high-pressure oil pipe, and become unstable. The oil supply is serious or even unable to supply. Due to the wear of the conical surface of the oil outlet seal, the fuel atomization quality is reduced, the fuel injection time is prolonged, the combustion process of the diesel generator is prolonged, and the performance index of the diesel generator is reduced. The wear of the pressure reducing ring belt and the seat hole is caused by the mechanical impurities caught in the gap when the pressure reducing ring belt enters the seat hole after the oil supply is cut off. The study found that after the decompression ring belt and the seat hole are worn, the valve clearance increases, the valve lift decreases, and the decompression effect decreases after unloading, which leads to an increase in the residual pressure in the tubing, an increase in oil supply, and an increase in oil supply speed. Not fast, there is a danger of unstable fuel injection, resulting in poor spraying, insufficient combustion, rough working of diesel generators, and reduced power. The diversion part of the delivery valve and the seat hole are worn, generally light, the gap increases after wear, and the delivery valve sloshes when moving up and down, affecting the positive direction of the cone, reducing the sealing performance, and causing partial wear of the decompression ring. For multi-cylinder diesel generators, the degree of wear of the delivery valve or plunger assembly is different, resulting in uneven fuel supply of each cylinder, inconsistent fuel injection pressure and fuel injection advance angle, resulting in unstable operation of the diesel generator.

3. Injector needle valve assembly: During operation, it is easy to malfunction due to the erosion of high-pressure diesel and high-temperature gas, the grinding of mechanical impurities, and the impact of the needle valve spring.

a. Needle valve assembly (fuel injection nozzle) wear: The parts where needle valve assembly often wears out are the sealing cone surface, the needle valve guide part and the inverted cone for atomization. The main reason for the wear of the oil seal cone is the impact of the injector spring and the scouring effect of impurities in the diesel. When the sealing cone surface is worn, the air tightness of the nozzle becomes poor, so that the pressure of the nozzle head cannot be increased, resulting in poor atomization and oil dripping, causing the diesel engine to emit black smoke. In addition, when the sealing performance of the fuel injection nozzle becomes poor, the high-pressure gas will easily escape into the fuel injection nozzle. In severe cases, the fuel injection nozzle may be burned out or the fuel may be burnt, causing the valve to jam.

When impurities are introduced into the diesel, the needle valve and the guide part of the fuel injection nozzle are worn out. Most of the wear occurs at the lower end of the guide. If the wear is serious, it will cause the nozzle to increase the fuel return, reduce the fuel supply, reduce the fuel injection pressure, and delay the fuel injection, which will cause the diesel generator to drop in power and even fail to work with load.

b. Needle valve stuck: The main reasons for the needle valve stuck include: diesel generator load is too large. Because the nozzle is overheated, the working temperature is too high, the cooling is not good, the needle valve is stuck and deformed; the needle valve lift is too long, the seating time is prolonged, the diesel pressure in the cavity before seating is lower than the pressure in the cylinder, causing gas to flow back from the fuel injection port to the inner cavity causes the needle valve to be stuck. Due to impurities in the diesel inlet or serious carbon deposits near the nozzle hole, the injector spring becomes soft or the injection pressure is softened or the injection pressure is adjusted too low, resulting in the needle valve cannot be closed in time, and the gas enter the nozzle, causing the pinhole reading to burn out and deform.

When the needle valve is in the open state, the fuel sprayed by the injector is not atomized well, burns incompletely, and emits black smoke; at the same time, the unburned fuel will also wash away the cylinder liner and other components, accelerating the wear of the cylinder liner and other components .

When the valve is closed, no matter how high the pressure of the fuel injection pump is, the needle valve cannot be opened, making the cylinder unable to work.

Change the injection pressure. During the operation of the internal combustion engine, the fuel injection pressure often changes, which causes the fuel injection pressure to be high or low. Too high fuel injection pressure will cause early wear of fuel injection pump plunger parts and fuel injectors during use, and sometimes expand high-pressure fuel pipes, and cylinder pressure will be generated when diesel generators work, low fuel injection pressure will cause fuel atomization poor, the nozzle is easy to deposit carbon and difficult to start. The main reason for the oil pressure change is that the pressure regulating elasticity is reduced or broken, which reduces the fuel injection pressure, the gap between the needle valve guide part and the needle valve body or the needle valve cone is not tightly sealed, which will also reduce the fuel injection pressure. When the valve is closed, the valve is stuck or the injection hole is blocked, which will increase the injection pressure.

Change of fuel supply advance angle. The fuel injection advance angle has a direct impact on the combustion performance. Because it is troublesome to measure the advance angle of oil, it is often necessary to measure the advance angle of oil supply. The fuel supply advance angle has a great influence on the performance of diesel generators, mainly affecting its economy, boost rate and maximum combustion pressure. If the fuel supply advance angle is too large, the fuel will burn more in the compression process. Not only does the negative compression work increase the fuel consumption rate. The power drops, but the fuel supply advance angle is too large, resulting in a long ignition delay period and a pressure increase rate. And the maximum combustion pressure rises rapidly, and the work is rough. If the fuel supply advance angle is too small, the fuel cannot burn rapidly near the top dead center, and then the combustion volume increases. Although the maximum fuel pressure decreases, the fuel consumption rate and exhaust temperature increase, and the diesel generator overheats.

Therefore, in each working condition, there is an optimal fuel supply advance angle, and the fuel consumption rate is the lowest at this time. The fuel supply advance angle often changes during the use of diesel engines. The main reasons are:

1. The fuel injection pump coupling connecting plate fixing bolts are shifted due to looseness, the fuel supply advance angle of each cylinder is delayed. 

2. Fuel injection pumps The adjustment bolt on the roller tappet is loose, which changes the advance angle of the fuel supply of a single cylinder.

3. The needle valve of individual injectors is not tightly closed or the fuel injection pressure is reduced. In addition, the oil outlet is not closed tightly, resulting in single cylinder fuel injection The advance angle is advanced.

4. When the injection pressure is adjusted too large, the advance angle will decrease.

5. The wear of the fuel injection pump roller tappet, oil pump cam, plunger and sleeve will reduce the fuel supply advance angle.

The low-pressure tubing is blocked or leaking. Blockage or air leakage in the low-pressure oil circuit will cause insufficient power of the diesel generator or difficulty in starting. The reason is that after the oil circuit is blocked or the air enters, the effective overflow of the fuel will be greatly reduced, which will cause insufficient fuel supply of the diesel generator, resulting in insufficient power or start-up difficulties.

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