Analysis of The Causes of Diesel Fuel in The Oil Sump

First, PT fuel pump

The main function of the PT fuel pump is to deliver the fuel plus low pressure (about 0.8~1.2MPa) to the injector. When the spindle oil seal at the PT pump coupling fails, the fuel will pass through the oil seal and enter the oil sump through the timing gear box. In this case, the PT pump spindle oil seal must be replaced.

The PT pump outlet has an electromagnetic and manual dual-purpose shut-off valve. When the ignition switch is turned on, the electromagnetic cut-off valve is opened and the oil circuit is turned on. When the ignition switch is turned off, the shut-off valve seal ring is closed under the action of the spring piece, and the oil passage is cut off. When the shut-off valve seal fails or the diesel engine works for a period of time, the electromagnetic valve is not tightly closed due to impurities in the diesel fuel, and the fuel will flow to the injector through the shut-off valve and penetrate into the oil sump through the combustion chamber.

Second, the injector

The function of the injector is to measure and pressurize the fuel output from the PT pump (about 110~120MPa) and spray it into the combustion chamber. When the injector nozzle (normally about 0.2032mm) is too large or damaged, the fuel will drip into the combustion chamber and leak into the oil sump. At this time, it is necessary to dismantle and replace the abnormal injector. If the upper and lower O-ring seals of the injector fail, the fuel will enter the valve chamber and the combustion chamber through the seal ring at any time, and then penetrate into the oil sump.

Third, the fuel tank

The fuel tank of the PT fuel system has a high position. When the fuel is stopped, the fuel tank and the PT pump flow into the injector through the combustion chamber and penetrate into the oil sump. Moreover, due to the high fuel tank position, the oil return is not smooth, especially after the shutdown, the oil return pressure is reduced. If the fuel tank elevation is too high, the oil return cannot return to the fuel tank, and only enters the combustion chamber through the injector and enters the oil sump. .

The motor ‘& generator’ & diesel motor ‘& generator set and the same model #3 motor ‘&generator ‘&diesel motor’& generator set have had the failure to stop the machine, thus judging the cause of the existence, PT pump The outlet shut-off valve is faulty.

After checking the injector nozzle and the O-ring, everything is good, so the reason 2 does not exist.

After measuring the fuel tank oil level is basically maintained at 1400mm height, and the injector nozzle height is 1260mm, and this unit is V-type 12-cylinder arrangement, the spindle rotates 720&deg12 cylinders for one work, that is, every 60&deg has one cylinder work. Therefore, when the engine is shut down, the injector of a certain cylinder must be in the open position. In addition, if the stop solenoid valve is not strict, the diesel oil will enter the combustion chamber through the PT fuel pump and the injector, and the piston ring opening gap is large, and the diesel oil is thus Entering the oil sump, the cause three exists and is the main cause of the failure.

This inspection replaced the stop solenoid valve, and partially solved the problem. However, if the diesel engine enters the solenoid valve for a long time, the same problem will occur. Therefore, it is necessary to solve the problem fundamentally and reduce the fuel tank elevation. However, due to time, the diesel engine unit must be put into standby after the operation of the #4 steam turbine unit, so it is reserved for the next shutdown.

In addition to the cause of the diesel engine itself, this failure also has a reason to start the motor and the battery. After inspection, only one of the two starter motors can work normally and is replaced. The battery pack was also replaced because it could not provide the power required for startup. After the overhaul, the unit was commissioned and entered normal standby.

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