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

This example illustrates the importance of controlling the Engine condition. Unequal clearance or uneven wear of the valve bridge can lead to several issues such as:

· Imbalance in Valve Timing: Imbalanced airflow or exhaust flow, reduced efficiency and power

· Incomplete Valve Closure: Compression loss, potential misfires

· Stress on the Valve Train: Additional stress that can lead to premature wear or even failure

· Valve Burnout: Combustion gases can leak past the valve causing burnout

In summary, unequal clearance or uneven wear of the valve bridge can lead to significant engine problems, including loss of performance, increased wear on engine components, higher fuel consumption, and even catastrophic engine failure if left unaddressed.

Utilizing the Advance Combustion Engine measurement will help to prevent such situations and provide the opportunity to expand the life of Engine 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)