Failure analysis and condition monitoring of an open-loop oil system using ferrography

Condition monitoring of dynamic systems based on oil analysis is well known for closed-loop systems. The motivation for this work stemmed from repeating failures of Wankel engines. Failure analysis identified contact fatigue as the failure mechanism, but could not identify the cause. Thus, the objective of the work was to develop a method for condition monitoring of open-loop oil systems. A variety of analytical techniques was evaluated, including direct-reading ferrography, analytical ferrography combined with computational image analysis, atomic emission spectroscopy, and scanning electron microscopy combined with energy dispersive X-ray spectroscopy. Procedures for collection and separation of oil samples were developed. Analytical ferrography was found most useful in condition monitoring. Six engines were detected in their early failure stage. Those engines were disassembled, and contact fatigue failures in the bearing needles were observed. The quantitative image analysis allowed for a fairly objective rating of the wear level. The method developed in this work has already been implemented on a daily basis for monitoring the health of Wankel engines, with much success.