Piston ring lubrication and friction reduction through surface modification
Frictional at the piston ring/cylinder liner (PRCL) interface is the single most significant contributor to the mechanical loss in an internal combustion engine. The purpose of this study is to: (a) advance the understanding of the frictional loss phenomenon at the PRCL contact in internal combustion engines through correlation of the numerical models developed herein and previously obtained experimental results; (b) Examine methods of reducing the parasitic losses at the PRCL contact through the use of modified surfaces. Three mixed lubrication models of progressively increasing complexity are developed and used to investigate the tribological behavior of the PRCL contact. The first model utilizes a typical stochastic asperity contact model coupled with a cavitation enabled Reynolds equation. Lubrication regime transitions are investigated and compared to experimental results with good agreement. The second model utilizes a new, semi-deterministic approach to modeling the asperity contact pressure. It is shown that this method allows for more accurate prediction of friction in the case of non-Gaussian surfaces. The third model handles mixed lubrication using a fully deterministic approach, which allows the inclusion of surface modifications. Modified surfaces are shown to provide a significant (50-60%) decrease in the average frictional loss over the cycle. Two approaches for the numerical synthesis of honed cylinder liner surfaces are then described and compared to measured surfaces with good agreement. Experiments conducted with a small engine dynamometer show reduced friction in the presence of laser modified surfaces. ^
Farshid Sadeghi, Purdue University.