Predictive tool for frictional performance of piston ring-pack/liner conjunction

Abstract

A substantial portion of engine frictional losses come from piston-ring assembly. However, accurately measuring in-cylinder frictional losses under actual engine operation remains a challenge to the automotive industry, especially during design stages of engines. Hence, the study proposes a simplistic mathematical tool to simulate the effect of different piston ring profiles towards engine in-cylinder friction. The models are derived from Reynolds equation to determine contact pressure generated by the lubricant film formed between the ring and the liner. Friction generated by the ring pack is then computed using Greenwood and Williamson's rough surface contact model. It is found that friction from the top compression ring is the largest, followed by the second compression ring and the oil control ring (single rail), with total friction of 301.3 N. On top of this, emphasis should also be placed on the top compression ring because of its direct exposure towards the combustion chamber in the engine. The predicted film thickness and friction force also showed correlation to other models reported in literature. Hence, the proposed predictive tool prepares for a simple yet robust platform in predicting frictional losses of piston ring-pack/liner conjunction, allowing for improved fundamental understanding of internal combustion engine in-cylinder lubrication.