Analysis and Investigation of AE Cyl. Liner Cavitation Erosion 

Introduction
Engine type: 6DC-17 
Maker: Daihatsu 
560 kW, 900 rpm.

I.Fault Symptoms
To meet the crane’s power demand, Generators No. 1 and No. 3 were operated in parallel.
the duty engineer observed abnormally low exhaust gas temperatures (EGT) in Cylinder No. 6 of AE No. 3, with deviations increasing from 30°C to 50°C over successive checks. After adjusting fuel injection, EGT temporarily normalized. However, Generator No. 3 later tripped unexpectedly, causing a total blackout.

II. Fault Diagnosis and Resolution
1. Initial Checks
Fuel injection timing: Normal.
Fuel injectors and pumps: No visible defects in pressure testing or atomization.
Fuel supply lines: No blockages detected.
2. Further Investigation
When running test it was found that there was water rushing out of the indicator cock of cylinder No. 6, indicating that the cylinder head or liner of cylinder 6 was leaking water. Open the crankcase and find water, further confirming that there is water leakage inside cylinder 6.
Cylinder liner removal: Severe cavitation observed on the outer surface of Cylinder No. 6 (Figure 1), with pinhole perforations (Figure 2).

3. Corrective Actions
Replaced Cylinder No. 6 liner.
Post-voyage inspection revealed cavitation in all cylinders, with Cylinder No. 1 most severely affected (Figure 3). All liners were replaced after spare parts delivery.

III. Mechanism of Cavitation
Cavitation, a form of erosion caused by collapsing vapor bubbles in cooling water, occurs due to:
1.Piston side thrust: Induces liner vibration, generating pressure fluctuations.
2.Coolant dynamics: Localized low pressure triggers bubble formation, followed by implosions that erode the liner surface.

IV. Factors Influencing Cavitation and Mitigation Measures
1. Control Piston Side Thrust
Optimize combustion pressure and connecting rod geometry.
2. Reduce Liner Vibration
Tighten piston-liner clearance.
Increase liner thickness or stiffness.
3. Manage Coolant Conditions
Maintain lower coolant temperatures (<70°C).
Use treated water and air removal systems.
4. Inhibit Bubble Collapse
Add anti-cavitation additives to coolant.
5. Operational Controls
Avoid prolonged overloading or overspeeding.
6. Material Enhancements
Use cavitation-resistant materials (e.g., nodular cast iron).
Apply surface treatments (chromium plating, ceramic coating).
7. Maintenance Best Practices
Regular liner inspections and dimensional checks.
Ensure proper fuel atomization and cooling water treatment.
Tighten engine foundation bolts periodically.

V. Root Cause Analysis
Cavitation in AE No. 3 was attributed to:
1.Chronic overheating due to poor combustion (leaky injectors, carbon buildup).
2.Excessive liner-piston clearance (accelerated wear).
3.Loose foundation bolts amplifying vibrations.
4.Neglected coolant treatment and delayed overhaul schedules.

VI. Lessons Learned and Recommendations
1. Operational Risks
The blackout during cargo operations posed risks of crane failure, cargo drops, and personnel injury.
2. Management Actions
Enforce strict maintenance schedules (liner measurements, turbocharger overhauls).
Train engineers in injector refurbishment to reduce reliance on new parts.
Conduct regular coolant chemistry tests and dosing.
Strengthen oversight of maintenance records and technical compliance.

VII. Conclusion
While cavitation in wet-liner trunk-piston engines is challenging to eliminate entirely, proactive management—including optimized design, material selection, and rigorous maintenance—can significantly mitigate its impact. This case underscores the importance of disciplined operational practices and technical vigilance in marine engineering.