A coupled model for ring dynamics, gas flow, and oil flow through the ring grooves in IC engines

Abstract

Oil flows through ring/groove interface play a critical role in oil transport among different regions the piston ring pack of internal combustion engines. This thesis work is intended to improve the understanding and modeling capability on this important oil transport mechanism for better analysis in engine oil consumption. A model incorporating ring dynamics, gas flow, and oil flow was developed to study oil transport in the piston ring-pack system. The major new element of this new model is adaptation of a mass conserved two phase oil/gas flow sub-model. Doing so, the present model can describe the oil flows through the ring/groove interface in a consistent manner. The model was applied to a heavy duty diesel engine at maximum power condition and to a SI engine at engine-braking and moderate load conditions. In the diesel application, the model demonstrates that oil can be released through the second ring/groove interface during second ring flutter and ring/groove interface plays positive role in reducing oil consumption and oil residence time. On the other hand, oil can be pumped up into the top ring groove and combustion chamber through the top ring/groove interface at engine braking conditions in the SI engine. Both applications show that oil flow rate through ring/groove interface is most prominent during the period of the engine cycle when the ring motion and gas pressure exhibit dynamic behaviors, and thus show that the coupling of the ring dynamics and gas/oil flows in the present model is essential to predict the oil pumping through ring/groove interface.