The Effects of Oil Film Shape on Piston Ring and Liner Tribology Under Mixed Lubrication

Mechanical power loss reduction at lubricated reciprocating and rotating components is recognized as an approach to improve the efficiency and to reduce the emissions of Internal Combustion Engines (ICEs). To achieve these goals, the instantaneous investigation of lubrication characteristics is required. Piston ring pack is of paramount importance as it is known as major contributor to frictional losses and energy dissipation. Applying Reynolds equation and lubrication theory to study piston ring tribology, requires specifying of boundary conditions. Oil film characteristics (shape and thickness) and generated hydrodynamic pressure are under influence of considered boundary conditions. Besides, the type of selected boundary conditions affects analysis robustness and sensitivity. During engine strokes, piston ring enjoys hydrodynamic and mixed lubrication regimes. The principle aim of the current study is to examine the effects of alternative boundary conditions: Half Sommerfeld, oil separation and Reynolds cavitation and reformation conditions on piston ring tribology under isothermal mixed and hydrodynamic lubrication regimes. This article demonstrates that different boundary conditions are suited to different operating conditions with respect to load, speed and temperature as well as crank angle, i.e., relative position of ring with respect to the liner. Thicker oil film thickness has been calculated applying half Sommerfeld boundary conditions under either hydrodynamic or mixed lubrication regimes followed by oil separation due to larger effective of the ring width. It was observed that considering oil separation boundary conditions results in lower deviation from experimental data, followed by Sommerfeld boundary conditions under mixed lubrication.