Mapping lubricating film thickness, film extent and ring twist for the compression-ring in a firing internal combustion engine

Experiments were conducted on a firing, 1.6 l, Ford Duratec petrol engine fitted with a number of miniature transducers to record the capacitance between the sensor and piston rings. The apparatus can record ring data with high accuracy, good repeatability and very low noise allowing data capture from a 1.2 mm width piston-ring travelling at up to 20 ms−1. Novel post-processing has enabled the authors to map oil film thickness, oil-film extent and ring twist, simultaneously, across the cycle of a firing engine for a range of operating conditions. The compression ring is shown to sometimes exhibit a high frequency oscillation normal to the cylinder wall—a behaviour which has not been reported before.