Boundary Conditions for Reynolds Equation with Particular Reference to Piston Ring Lubrication

This paper considers the lubrication of the interface between a piston ring and cylinder wall, as encountered in reciprocating internal combustion engines and pumps, with the specific aim of evaluating alternative boundary conditions that can be applied when solving Reynolds equation. It is shown that different boundary conditions result from assuming different models of lubricant film cavitation in the interface and that the choice of boundary conditions can have a significant influence on the results of the analysis. Theoretical predictions of hydrodynamic pressure, lubricant film thickness and friction for the top piston ring of a single-cylinder diesel engine are presented for two alternative forms of cavitation which illustrate the sensitivity of the analysis to the choice of boundary conditions. In an attempt to gain an insight into the correct boundary conditions to use, a review is presented of available experimental data. This concludes that experimental data published to date fails to resolve clearly which boundary conditions are more appropriate or whether perhaps different boundary conditions are suited to different conditions of load, speed, temperature and degree of lubricant starvation.

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