Use of Surface Specific Flow Factors in a Multi-Physical Model of Power Cylinder Components

Abstract

New technologies are being introduced for power cylinder components at a faster rate due to the drive for better fuel economy and CO2 foot print reduction. This includes new and advanced coatings, materials, and surface textures. In turn, robust methods are needed to evaluate and optimize technologies to ensure optimal performance. Therefore, the study of tribological lubrication flow has become more pressing among power cylinder components. This thesis analyzes the modification of the Reynolds equation for computational efficiency by analyzing rough surfaces in the hydrodynamic flow regime through the use of flow factors. This analysis is aimed towards modeling the surface interactions and pressure variations across power cylinder components of an internal combustion engine, namely the piston ring and cylinder wall. These interacting surfaces were measured directly through the use of a profilometer. Through the use of these measured surface properties, surface specific flow factors are derived by numerical flow simulation. The statistical flow factors are obtained and implemented in the Reynolds equation to model the pressure and shear variations across the asperities of interacting surfaces. These flow factors can then be used to consider the effect of roughness in lubrication problems without deterministically modeling roughness. The derived flow factors make predictions that are significantly different than those in existing literature. This derivation methodology can be used in the determination of flow factors for any pair of interacting surfaces. The governing flow factors for a pair of surfaces are expressed as empirical relations in terms of the film ratio (h/σ). The flow factors are then applied to an initial analysis of a multi-physical model of power cylinder components in a two-dimensional axisymmetric case to consider roughness throughout the combustion cycle in order to evaluate tribological interactions.