Analysis and Methodology to Characterize Heat Transfer Phenomena in Automotive Turbochargers

In the present work a comprehensive study of turbocharger heat transfer phenomena is discussed, showing their relevance compared to gas enthalpy variations through the turbomachinery. The study provides an experimental methodology to consider the different heat fluxes in the turbocharger and modeling them by means of a lumped capacitance heat transfer model (HTM). The input data required for the model are obtained experimentally by a proper combination of both steady and transient tests. These tests are performed in different test benches, in which incompressible fluids (oil) and compressible fluids (gas) are used in a given sequence. The experimental data allows developing heat transfer correlations for the different turbocharger elements. These correlations take into account all the possible heat fluxes, discriminating between internal and external heat transfer. In order to analyze the relative importance of heat transfer phenomena in the predictability of the turbocharger performance and the different related variables; model results, in hot and cold conditions, have been compared with those provided by the standard technique, consisting on using look up maps (LUM) of the turbocharger. The analysis of these results evidences the highly diabatic operative areas of the turbocharger and it provides clearly ground rules for using hot or cold turbocharger maps. In addition, paper discussion advises about using or not aHTM, depending on the turbocharger variables and the operative conditions that one desires to predict. Paper concludes that an accurate prediction of gas temperatures at turbine and compressor outlet and of fluid temperatures at water and oil ports outlet is not always possible without considering heat transfer phenomena in the turbocharger.