Piston-ring performance: limitations from cavitation and friction

Purpose Cavitation in piston-ring lubrication is studied as part of the performance of piston-ring assemblies. Cavitation degrades performance in engineering applications and its effect is that it alters the oil film pressure, generated at the converging-diverging wedge of the interface. Studies tried to shed light to the phenomenon of cavitation and compare it with cavities that have been identified in bearings. The paper aims to discuss this issue. Design/methodology/approach Lubricant formulations were used for parametric study of oil film thickness (OFT) and friction providing the OFT throughout the stroke and LIF for OFT point measurements. Lubricant formulation affects cavitation appearance and behaviour when fully developed. Findings Cavitation affects the ring load carrying capacity. Different forms of cavitation were identified and their shape and size (length and width) is dictated from reciprocating speed and viscosity of the lubricant. A clear picture is given from both techniques and friction results give quantifiable data in terms of the effect in wear and cavitation, depending on the lubricant properties. Research limitations/implications Engine results are limited due to manufacturing difficulties of visualisation windows and oil starvation. Therefore, full stroke length sized windows were not an option and motoring tests were implemented due to materials limitations (adhesive and quartz windows). Lubricant manufacturer has to give data regarding the chemistry of the lubricants. Originality/value The contribution of cavitation in piston-ring lubrication OFT, friction measurements and lubricant parameters that try to shed light to the different forms of cavitation. A link between viscosity, cavitation, shear thinning properties, OFT and friction is given.