It was discovered in 1970 that certain gas turbine failures are preceded by an increase in electrostatic activity in the exhaust gases. Joint research by the Royal Aerospace Establishment and Stewart Hughes Limited demonstrated that this characteristic could be used to provide an on-line monitor of the precursors to these failures. An extension of the research applied the theory to the detection of foreign objects ingested into engine inlets. The characteristics and performance of both the Ingested Debris Monitoring System (IDMS) and Engine Distress Monitoring System (EDMS) were examined during a recent 2000 hours endurance trial of a Rolls-Royce Marine Spey gas turbine.

The EDMS produced clear evidence of the minor combustor degradation that occurred steadily throughout the trial and also reflected the absence of other engine damage. IDMS data showed that few significant debris particles passed through the engine. Video endoscope and visual inspection confirmed these results. Debris seeding trials further explored the capability of the IDMS to identify the damaging nature of debris and to assess the EDMS signature of consequential engine damage.

The paper concludes that electrostatic monitoring at engine inlet and exhaust can identify the ingestion of debris, consequential engine damage and the onset of unexpected distresses caused by blade rubs or combustor degradation. The technique shows potential to provide early warning of certain types of engine damage to Engineer Officers at sea and development into a rugged gas path condition monitoring system continues.

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