Effect of translucence of engineering ceramics on heat transfer in diesel engines: Final report

Abstract

This report addresses the question of translucence of ceramics, and investigates how it influences the net heat transfer to the engine structure. A two flux radiation model was developed to describe radiation within the ceramic, and it was checked and validated against accurate literature results. Based on it, a coupled radiation/conduction model of a ceramic was developed, and it was used in conjunction with time-dependent boundary conditions describing gas-phase heat transfer arising in a heavy duty truck engine operating at its rated point. The model was applied to limiting cases of fully opaque and full transparent materials, and also in a parametric study covering a wide range of ceramic radiative properties encompassing the range of such properties considered possible for heat barrier ceramics. The material thickness and conductivity were varied as well. The results showed that translucence can have significant detrimental effects on heat barrier effectiveness under realistic diesel engine conditions. The most important properties are the absorption and scattering coefficients of the ceramics. As these become less opaque, the total heat flux through the ceramic layer increases. For low conductivity ceramics this increase can amount to 50% and more. Significant effects begin to be felt for absorption coefficients smallermore » than 10,000 m/sup -1/ and scattering coefficients smaller than 20,000 m/sup -1/. An important parameter is also the heat barrier thermal conductance, i.e., the ratio of thermal conductivity to the layer thickness. It is recommended that radiative properties be among the properties that are measured and reported for ceramic materials. If a particular ceramic is found too translucent, some tailoring of its radiative properties, e.g., by additives, should be considered. 20 refs., 37 figs., 3 tabs. « less

Keywords

This publication has 0 references indexed in Scilit: