Heat Transfer Effects on Performance Map of a Turbocharger Compressor for Automotive Application

In the last few years, the effect of diabatic test conditions on compressor performance maps has been widely investigated leading some authors to propose different correction models. The accuracy of performance maps constitutes the basis of the turbocharger matching with the engine, for which 1D procedures are more and more adopted. The classical quasi-steady approach generally used is based on the employment of compressor and turbine characteristic maps assuming adiabatic turbocharger conditions. The aim of the paper is to investigate the effect of heat transfer phenomena on the experimental definition of turbocharger maps, focusing on compressor performance. This work was developed within a collaboration between the Polytechnic School of the University of Genoa and CRITT M2A. The compressor steady flow behavior was analyzed through tests performed on different test rigs operating at the University of Genoa and at CRITT M2A, under various heat transfer conditions. The experimental campaign was developed on a small waste-gated turbocharger for gasoline engine application considering the effect of different heat transfer states by varying turbine inlet temperature, oil and coolant temperature and compressor inlet pressure. Non-destructive measurements were performed in order to get a proper database, including quasi-adiabatic maps, as a reference for the comparison of different correction models. A first comparison between raw results highlighted differences up to 30 percentage points of compressor efficiency at the lowest tested turbocharger rotational speed (30% of maximum speed). Three different correction models, selected in the available open literature for their simplicity and applicability especially in terms of input data required (geometrical and thermo-physical turbocharger characteristics) were then applied after slight modifications. The relevant results are presented and discussed in the paper.