Abstract
An improved understanding of lubrication within the piston ring pack is expected to contribute to efforts aimed at improving the fuel economy of automotive engines. However, most studies of frictional losses within the piston ring-pack use viscometric data for ‘fresh’ lubricants. The changes that occur to the viscometric properties of the lubricant in a working engine are not generally taken into account. The lubricant in an engine is subjected to a harsh physical environment, and the aggressive chemistry that takes place in the vicinity of the top piston ring causes lubricant degradation by both evaporation of the lower boiling point components and by oxidation. Top ring zone oil sampling studies show that this degradation changes the viscometric properties of the lubricant. Measured viscometric data have been used in a piston ring pack model to estimate the effects of oil degradation on frictional power losses within the ring pack. In an extreme case, degradation increased these losses by up to 40%.
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