Influence of Surface Roughness Factor in Modeling Isothermal Piston Skirts Lubrication in Initial Engine Start Up

摘要

Initial engine start-up is an occasion when wear of the interacting piston skirts and the liner surfaces cannot be avoided. Adhesive wear is more pronounced in a few initial cycles of the cold engine start-up. It occurs due to the absence of a fully established lubricant film between the skirt and the liner surfaces. The skirt and the liner surfaces are essentially rough with different asperity amplitudes. The different deterministic asperity amplitudes are anticipated to influence the formation of hydrodynamic lubricating film at low start-up loads significantly. This study numerically models the hydrodynamic lubrication of piston skirts by defining the secondary piston motion and the geometry of the interacting skirts and the liner surfaces as functions of 720 degree crank rotation cycle. The 2-D Reynolds equation is solved numerically after incorporating the different asperity amplitudes to study their influence on the generated hydrodynamic pressures, lubricant film thickness, and secondary piston displacements. A high viscosity-grade engine lubricant, low load and engine start-up speed under isothermal conditions are some of the salient characteristics of the 2-D model. The simulation results show that the different roughness asperity amplitudes improve the hydrodynamic film thickness and affect the piston secondary displacements, surface energy transfer, hydrodynamic pressures and load-carrying capacity of the film in a few engine start-up cycles.