Diesel Engine Fuel Shut Off Fault Analysis

Structure of G1 Type Fuel Shut Off

There are two types of fuel shut off solenoid, the G1 type for constant-speed diesel engines such as generators, and the J2 type for variable-speed diesel engines such as marine main engines. The G1 type of fuel cutoff device is provided with a stop piston to cut off fuel or a fuel control piston to control excessive fuel injection, with the control piston and cutoff piston aligned back and forth. The unit is controlled by a common linkage that places the rack in the stop or control position and is controlled by the control air of each cylinder.

Failure Phenomenon

During the period of anchoring and waiting for cargo in the anchorage outside a port, a ship was unlisted from the grid after the regular unlisting operation, and the power-generating diesel engine which was just connected to the grid had a fault of slowly decreasing load, which caused some of the power-using equipment to unlock by itself and affected the normal work of the cabin. Under the leadership of the chief engineer and the engineer in charge, the cabin crew unhooked the engine and analyzed and investigated the fault.

Failure Analysis

1. Since the diesel engine can start normally, the fault of the starting system components such as the starter motor, starting solenoid valve, and starting line pressure-reducing valve can be excluded.
2. The daily maintenance of the diesel engine was carried out according to the plan, and the total running time was about 11,326 h when the fault occurred, so the fault could be basically excluded due to the aging of the machine parts.

The governor was interchangeably tested and functioned normally. Therefore, the fault is not caused by the governor.

Preliminary Troubleshooting

1. Clean each filter in the fuel supply line of the fuel system. The most common reason for the diesel engine not being able to carry the rated load is a fuel system failure, which is manifested by dirty filters, insufficient flow due to internal leakage of the supply pump or booster pump in the fuel supply unit, etc. Therefore, the cabin crew quickly switched the inlet filter to standby and cleaned the filter in front of the booster pump in the fuel supply unit. After checking, the diesel engine was started and the fault remained.
2. The troubleshooting of fuel injection equipment. The diesel engine can not withstand the higher load, which may also be because the injector can not provide the amount of oil supply required for large loads. The possible reason is that the injector nozzles are partially blocked. The cabin crew thought this was less likely but still switched the engine to a diesel supply for testing. After switching to diesel fuel and starting, the fault remained.
3. Turbocharger inspection and troubleshooting. Another important reason why the diesel engine could not carry a larger load was that the turbocharger could not provide enough intake of air. The fault analysis of the inspection method is used, after starting the engine, with a probe rod to listen to the turbocharger bearing parts and impeller parts whether there is a strange sound, and found no abnormalities. At the same time, disassembly of the machine with the oil filter, the filter at the bottom of the oil sludge sampling after observation with a magnifying glass, did not find too much metal, which can be initially ruled out as the turbocharger fault.

Diesel engines automatically reduce the load, but also may be due to the failure of the lubricating oil system or cooling water system, resulting in solenoid valve action, to the operating system to reduce the speed of the signal. Therefore, under the organization of the motor officer and the engineer in charge, members of the engine room department conducted a preliminary check of the security system of the machine. According to the manual, the diesel engine was equipped with a double security system, i.e. the starting system of this model was equipped with the following security mechanisms to ensure that the system could start under permissible conditions and could control or cut off the fuel supply in time to reduce speed or even stop when a stop signal was received.

Final Troubleshooting

After testing and analysis, found that the above solenoid valve in the fuel control solenoid valve (88L) spool has a jam, resulting in part of the control air can constantly enter the G1 fuel cut-off/controller, so that the control valve spool always subject to a leftward force, which will pull the throttle to reduce the direction of movement, thus causing the diesel engine can not bear a larger load. The fuel control solenoid valve (88L) from the side of the machine to remove, disassemble and cleaned, lubricate the spool of the slide valve to live, after the installation of the diesel engine, can gradually carry a larger load, so far the fault is eliminated.