MODELING REALISTIC PISTON SKIRTS & I ST COMPRESSION RING EHL IN THE INITIAL ENGINE START UP

Abstract

The automobile manufacturers aspire to improve the engine design and enhance its life apart from optimizing the energy usage in the actual engine operation. A major concern at the time of the initial start up at the low loads and speed conditions is the wear of an engine. A significant proportion of the engine life gets compromised due to the adhesive engine start up wear. The start up wear does not exist during the normal engine operation due to the fully established elastohydrodynamic lubricating (EHL) film between the interacting surfaces of the piston assembly and the cylinder liner at the high loads, speeds and the optimum piston-to-bore radial clearances. Such arrangements do not exist in a few initial engine start up cycles. Resultantly, the piston skirts and the 1 st compression ring establish a physical contact with the liner and adhesive wear occurs. This PhD research work numerically models the lubrication of the piston skirts and the 1 st compression ring in the initial engine start up. The 2-D hydrodynamic and EHL models of the piston skirts are developed in the initial engine start up conditions. The initial engine start up conditions cover the secondary transverse piston displacements and the different start up speeds, radial clearances & viscosity-grades of an engine lubricant. The realistic aspects include the isothermal & adiabatic conditions, the steady-state and transient conditions, the Newtonian and non-Newtonian engine lubricant behavior, the surface roughness factors of the piston skirts and the liner. These aspects are modeled, studied and analyzed separately as part of the hydrodynamic and EHL models of the skirts. The 1-D and the 2-D steady-state isothermal Newtonian lubrication models of 1 st compression ring are developed as applicable to the initial engine start up conditions. The simulation analysis are studied to optimize the different realistic aspects/characteristics in an effort to reduce the engine start up wear.