Turbulence Driven Convective Heat Transfer in a Direct Injection Diesel Engine

Abstract

There is a history of over 70 years in the study of heat transfer in internal combustion engines. Formerly, interest is concentrated on the global heat transfer for cooling load predicting and engine cycle simulation. More recently, there is growing interest in the study of spatial heat transfer in order to be able to predict better the combustion and the pollutant formation processes which are progressing from the single zone models to the multi-zone or multidimensional models. In a diesel engine, there are two forms of heat transfer, namely, convection and radiation. Convection is the major form of heat transfer but radiation generated at the diffusion combustion stage can account for 10% to 50% of the total heat flux. Convective heat transfer has been considered to be highly dependent on the in-cylinder flow which includes the turbulence level set up by the engine motion and by the combustion process. In most previous studies, the major driving force for convection is the tangential velocity component. However recent experiments performed by the authors indicate that at a point quite near to the cylinder axis, where the flow is supposed to be very low, the magnitude of heat flux is comparable with locations where the tangential flow is very high. In this paper, a new approach is proposed to model the convective heat flux.