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Introduction
AE type: MAN B&W 6L23/30H , 720 rpm.
Auxiliary Engine No. 4 failed to start. The specific symptom was:
Local startup attempt: Engine speed failed to reach the ignition threshold of 110 rpm, resulting in startup failure. Repeated attempts yielded the same result.
I. Fault Diagnosis
A systematic troubleshooting approach was applied to inspect the AE and its systems:
1.Fuel System Check
Fuel pressure and temperature were normal. No blockages, leaks, air bubbles, or contaminants were detected.
Conclusion: Fuel system ruled out.
2.Starting Air System Check
Air pressure and supply were sufficient. The starting motor operated normally, confirming adequate cranking speed.
3.Governor Inspection
Stop lever and solenoid valve actuator moved freely. No components were stuck in the "stop" position.
Conclusion: Governor system ruled out.
4.Regulating rod and device Check
Fuel pump rack for all cylinders moved smoothly. No signs of wear or leakage in fuel injection pumps.
5.Fuel Injection Timing Verification
Injection timing was within specifications. No premature or delayed injection observed.
6.Intake/exhaust valves moved freely. Camshaft and drive components showed no abnormalities.
7.Overspeed Device Check
No alarms or visible defects in the overspeed device.
II. Root Cause Identification
During inspection of the Lambda cylinder (part of the overspeed protection system), it was found that the piston rod remained extended, forcing the ‘Spring loaded pull rod, complete’ to the "zero" position.
Lambda Cylinder Function:
Normally, the Lambda cylinder activates only during emergency stops or overload conditions.
During normal operation, the piston retracts under spring force.
Fault Analysis:
Compressed air was continuously supplied to the Lambda cylinder, overriding its spring return mechanism.
Root Cause: Malfunction in the mechanical overspeed device, which erroneously triggered the Lambda cylinder.
III. Overspeed Protection Device Mechanism
Design and Operation (Figure):
Installed on the lubricating oil pump cover, driven by the crankshaft.
At speeds exceeding 860 rpm, flyweight (191) actuate a lever (274), which opens an air valve to pressurize the Lambda cylinder.
Manual reset buttons (022 and 357) allow for emergency operation.
Fault Investigation:
The mechanical overspeed device was stuck in the "trip" position, preventing reset.
Corrective Action: Disassembly, replacement of faulty components, and system reset restored normal operation.
IV. Expanded Inspection
All auxiliary engines were inspected:
No. 1 Engine: Functional.
No. 2 and No. 5 Engines: Contaminated emergency operation ports caused control shaft (370) jamming.
No. 3 Engine: Clogged pneumatic valve.
Corrective Measures:
Replaced overspeed protection assemblies for No. 2 and No. 5 engines.
Cleaned pneumatic valves for No. 3 engine.
Installed plugs on emergency ports to prevent debris ingress.
Preventive Recommendations:
1.Conduct regular manual reset tests on overspeed protection devices.
2.Maintain air filters and drain moisture from air lines periodically.
V. Lessons Learned
This incident highlights the importance of:
Proactive Maintenance: Regular checks of safety-critical systems.
Understanding System Logic: Clear knowledge of device operation principles.
Contamination Control: Sealing exposed ports and ensuring clean air supply.
