With increasingly stringent legislation controlling vehicular emissions being introduced, efficiency gains in combustion engines continue to be desirable to OEMs. Reducing FMEP provides one such route and with piston-cylinder interactions accounting for around 40% [1 & 2] of a typical engines frictional losses warrants research directed at improvements.
Though developments are being driven by numerical techniques, there is still the need for robust experimental data to evaluate these models. One of the measurable parameters which offers a direct link between simulation and ‘the real world’ is lubricant film thickness within the contact. For over half a decade, various techniques have been used to monitor film thickness but can broadly be split into those exploiting the thickness related electrical, optical or acoustical properties of the lubricant.
This paper provides a review of the different techniques, their capabilities and industrial applicability with focus on the relatively new technique of ultrasonic measurement, which shows promise as a ‘road going’ method being both non-invasive and highly portable.