Numerical investigation on lubrication of metal packing using an improved thermo-mixed elastohydrodynamic approach

Abstract

This study extends the thermo-mixed elastohydrodynamic lubrication (TMEHL) model coupled with the GT contact model to investigate the lubrication behavior of packing in ultra-high-pressure ethylene compressors, and improves the lubrication model by refitting the relationship between asperity load and film thickness within the Greenwood–Tripp (GT) framework. The model explicitly incorporates the plunger's elastic modulus and surface roughness, addressing limitations of conventional approaches. Lubrication and thermal behavior are analyzed over the entire stroke, with emphasis on the effects of surface roughness and environmental temperature. Results indicate that hydrodynamic pressure peaks at the inlet zone and increases with sliding velocity, while asperity contact primarily occurs in regions of concentrated static contact pressure. The predicted film thickness ratio indicates that the interface predominantly operates under mixed lubrication, with minimum thickness and maximum friction at the end of compression. The average oil film temperature, influenced by sliding velocity and asperity contact pressure, reaches 416 K at a crank angle (CA) of 120°. Increasing surface roughness enhances asperity load support and raises lubricant temperature, while the initial improvement in film thickness ratio diminishes with roughness. Higher environmental temperatures reduce lubricant viscosity and fluid pressure, raising friction at high sliding velocities. Leakage is primarily governed by velocity, which is higher during the outstroke, with minimal influence of ambient temperature.