Modeling Viscous Isothermal Piston Skirts EHL in Very Low Initial Engine Start Up Speeds

Abstract

In the normal low-speed engine operation, elastohydrodynamic lubrication (EHL) of piston skirts and lubricant rheology reduce friction and prevent wear. In a few initial start up cycles, a very low engine speed and absence of EHL cause adhesive wear. This study models hydrodynamic and EHL of piston skirts in the initial very low cold engine start up speed by using a high viscosity lubricant. The 2-D Reynolds equation is solved and inverse solution technique is used to calculate the pressures and film thickness profiles in the hydrodynamic and EHL regimes, respectively. The work is extended to investigate the effects of three very low initial engine start up speeds on the transverse eccentricities of piston skirts, film thickness profiles and pressure fields in the hydrodynamic and EHL regimes. Despite using a viscous lubricant, thin EHL film profiles are generated at low start up speeds. This study suggests very low speed optimization in the cold initial engine start up conditions to prevent piston wear under isothermal conditions.