Mixed lubrication of piston compression ring with deformed cylinder liner during warm-up of spark ignition engine

Emerging clearances caused by out-of-round cylinder bores alter the tribological performance of piston compression rings. This change in performance intensifies during engine warm-up. To analyze the development of tribo-characteristics, a 2D mixed lubrication model is considered in the simulation of piston ring conjunction with a distorted bore during the entire warm-up period of a four-stroke spark ignition engine. Piston ring axial dynamics and conformability analyses are incorporated in the simulation. Oil film thickness, frictional loss, asperity interaction, and lubricant flow to the combustion chamber are investigated. The effect of the magnitude of bore distortion on ring conformability, oil transport, and energy loss per warm-up is also evaluated. Variations in oil transport and energy loss per warm-up per unit change in bore distortion are subsequently analyzed. Results show that despite the high film thickness, frictional losses remain substantially high during the initial warm-up phase. An uneven lubricating film resulting from bore non-circularity reduces this energy loss, but drastically increases the already augmented oil transport during the cold engine start-up. The temperature-dependent variation in performance is sensitive to bore distortions.