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What Cause Uneven Delivery Fuel of Diesel Generator Set

Jul. 09, 2020

In generally, uneven delivery fuel of diesel generator set maybe cause diesel engine high fuel consumption or failure. At this time, we should find out the reasons and adjust fuel injection pump.


What Cause Uneven Delivery Fuel of Diesel Generator Set?

1.Mechanical failure

After a long-term use of genset, due to the loose shaft coupling or large clearance of fuel injection pump, the wear of driving gear and the increase of side clearance will also affect the fuel supply uneven of each cylinder. In addition, the fuel leakage caused by high pressure oil pipe joint due to frequent vibration or insufficient tightening, as well as excessive tightening force will lead to uneven fuel supply of each cylinder.

In addition, among the springs of fuel injection pump and governor, the piston spring with strong force, large deformation and high working frequency is the plunger spring. Therefore, the fracture frequency is higher. In light cases, the fuel injection quantity is reduced, the fuel injection quantity is uneven, the injection interval time of each cylinder is out of tolerance, and the injection start time is delayed; in the heavy case, the fuel supply is interrupted or even can not be supplied.

2.When commissioning there is uneven delivery fuel problem

When fuel injection pump commissioning on the test bench, it is required that the nonuniformity of the oil injection should be less than 3%. But during the commissioning, because the length, shape, bore of special fuel injector and high pressure oil pipe for test bench is not all same as original one, and difference of commissioning technology, after installing the fuel injection pump, the nonuniformity of the oil injected into the cylinder is often more than 3%.

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3.The difference between commissioning state and using condition

The fuel injection pump is debugged at normal temperature on the test bench, while the fuel injection pump on diesel engine is installed and used under the conditions of cylinder compression end, cylinder temperature up to 500-700 ℃ and pressure 3-5mpa. There is a big difference between them.

When the locomotive is working, the temperature of the fuel injection pump and injector reaches 90 ℃, which will also cause the viscosity of diesel oil to decrease. As a result, the internal leakage of plunger and needle valve coupling parts increases, and the amount of oil return is more than that during commissioning. According to the measurement, the actual amount of oil injected into the cylinder by the fuel injection pump is only about 80% of the debugging amount of the test bench. Although the oil pump debugging personnel will consider this factor, it is impossible to accurately grasp it.

In addition, the temperature and pressure of each cylinder after compression will be different due to the different wear or sealing degree of cylinder piston and valve train. Even if the fuel injection pump has been debugged on the test bench, the fuel supply of each cylinder will be uneven after being installed and used.


So we should adjust the fuel injection pump after installed, but how to adjust? See as below.

According to the exhaust temperature, pressure or smoke color of each cylinder, the actual working condition and combustion degree can be judged, so as to determine whether the fuel delivery quantity of the cylinder is too much or too little, whether the fuel supply time is too early or too late, and then adjust it again. By properly adjusting the fuel supply quantity and fuel supply time of each cylinder, the fuel injection pump can supply oil to each cylinder according to the principle of distribution on demand, so as to eliminate the actual difference of each cylinder.


1.Start diesel generator set, idle speed for 2~3min, if the temperature of a certain cylinder is too high, it can be preliminarily concluded that the fuel supply of this cylinder is too much.  

2.Check the fuel supply advance angle.

Generally, the oil spill method can be used to check the oil supply advance angle, that is, the high-pressure oil pipe joint at one end of the oil pump is loosened, the joint connecting the injector end is removed, the oil pipe is turned to the horizontal position, and then the high-pressure oil pipe joint of the oil pump is tightened, the throttle is pulled to the maximum position, and the decompression shaking is opened until a few drops of diesel oil emerge from the outlet of the high-pressure oil pipe. Clean the diesel oil at the outlet of the oil pipe, and then slowly turn the flywheel. At the same time, pay attention to observe the oil level at the outlet of high-pressure oil pipe, and stop turning the flywheel immediately when it starts to move up. At this time, the notch on the water tank or engine block should be aligned between 16 ~ 20° before TDC of flywheel. 

If there is oil overflow before the alignment, it means that the oil supply advance angle is too large and the oil supply is too early; if the oil overflow occurs only after exceeding the oil supply advance angle, it indicates that the oil supply advance angle is too small and the oil supply is too late.

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After the above initial adjustment, check whether the exhaust temperature of each cylinder is consistent. If the normal operation of the engine cannot be restored, measure whether the cylinder pressure is within the allowable range, replace the piston ring or grind the valve if necessary, and check whether the atomization condition and opening pressure of the fuel injector are normal.


1. After the fuel injection pump is installed, adjust the fuel delivery time according to the specified standard, and remove the exhaust manifold to observe the working condition of each cylinder.

When the engine temperature exceeds 50 ℃, increase the throttle and let the engine run at the rated speed. At the same time, check the smoke color of each exhaust port and listen to the sound of the cylinder. If a certain cylinder emits black smoke, it means that the fuel supply is too large. Pull the adjusting gear rod of the fuel injection pump to the oil stop direction, loosen the locking screw on the adjusting gear, insert a fine iron rod into the small hole of the oil quantity control sleeve, tap it gently with a hammer, and turn it to the right, then the fuel supply can be reduced, otherwise, it will increase.


2. When a certain cylinder of the diesel generator has a crisp knocking sound, and it is difficult to start, it indicates that the oil supply starts too early. If the temperature of a certain cylinder is too high, or even there is flame, it may be that the fuel supply start time is too late. The adjustment of starting time of oil supply for each cylinder is determined by the position of oil pump plunger. When the starting time of oil supply is too late, screw out the timing adjusting nut and screw. If the starting time of oil supply is too early, tighten the screw. 

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