Marine Diesel Engine Diagnostic

Reference

In engines with two intake and exhaust valves, a pattern similar to that shown in Fig. 1 will often be seen, where the two intake or exhaust valves (exhaust valves closing signal are shown in the middle of the figure) are closing at slightly different times. (Two specific impact signals – one after the other) This is due to unequal lash settings or unequal wear in the components. Some differences are permissible. [1]

Fig. 1 Example of vibration pattern for exhaust valves with unequal bridge clearance setting or wear

Measurement and vibration data

Our service engineer performed a scheduled Advanced Combustion Engine Measurement on one of our customer Auxiliary Engines. Below is the Cylinder head with highlighted measurement points.

Fig. 2 Cylinder head measurement points Inlet valve side (Top cover removed for inspection)

Vibrations were measured by an accelerometer and ultrasonic sensor. Vibration traces are shown in Figure 3.

Fig. 3 High-frequency, Raw-frequency and Ultrasonic vibration – measured on the cylinder head with visible unequal bridge clearance setting or wear pattern

It is very clearly seen that the high-frequency vibrations for the inlet valve closing (-200° – -100°) show the same pattern as described in Reference. Additionally, the raw-frequency and Ultrasonic vibration traces also indicate similar issues on the inlet valve. This result let us to recommend checking the valve bridge condition and clearance.

Feedback and new measurement

After receiving positive feedback from the crew – The inlet valve bridge clearance was readjusted. Our Service Engineer remasured the Engine cylinder head. New vibration traces are shown in Figure 4.

The new vibrations now show only a single closing signal for the Inlet valves. Figure 4.

Fig. 4 High-frequency, Raw-frequency and Ultrasonic vibration – measured on the cylinder head with visible equal bridge clearance setting

Conclusion

Marine Diesel Engine Diagnostic: Importance of Engine Condition Monitoring

Effective Marine Diesel Engine Diagnostic is crucial in maintaining optimal engine performance. Unequal clearance or uneven wear of the valve bridge can result in several critical issues, including:

Imbalance in Valve Timing – Leads to disrupted airflow or exhaust flow, reducing efficiency and power output.
Incomplete Valve Closure – Causes compression loss and potential misfires, impacting engine stability.
Excessive Stress on the Valve Train – Increases strain on components, leading to premature wear or failure.
Valve Burnout – Leaking combustion gases can cause overheating and valve damage.

If left unaddressed, these issues can lead to severe engine problems such as performance loss, accelerated wear on engine components, increased fuel consumption, and even catastrophic engine failure.

By implementing Advanced Combustion Engine Measurement techniques as part of a Marine Diesel Engine Diagnostic strategy, operators can prevent such failures, enhance engine efficiency, and extend the lifespan of critical components.

Some data presented in this article were sourced from the Diesel Engine Analysis Guide by EPRI, available at this link (https://www.scribd.com/document/382755927/Diesel-Engine-Analysis-Guide-EPRI)