Piston Ring Thermal Transient Effects on Lubricant Temperatures in Advanced Engines

One class of advanced diesel engines operates with low heat rejection and high operating temperatures; piston-ring / liner lubrication is a major problem for these engines. This study attempts to illustrate the time-dependent thermal environment around the top piston ring and lubricant in these advanced engines. Particular emphasis will be placed on the maximum lubricant temperature. The analysis starts with a standard cycle simulation and a global finite-element analysis of the piston and liner in relative motion. A more detailed finite-element model, which considers variable oil film thickness on the liner, focuses on the top ring and lubricant and uses the groove and liner temperatures generated in the global analysis as boundary conditions. Results for different heat rejection engine configurations are presented. We observe that because of major transient effects, high lubricant temperature is experienced not only at top ring reversal but also down the liner to bottom ring reversal.