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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 aim of the paper is to investigate the effect of heat transfer phenomena on the experimental definition of turbocharger maps, focusing on turbine performance. An experimental investigation on a small turbocharger for automotive application has been carried out and presented. The study focused onto the effects of internal heat transfer on turbine thermomechanical efficiency. The experimental campaign was developed considering the effect of different heat transfer state by varying turbine inlet temperature, oil and coolant temperature and compressor inlet pressure. An original model previously developed by the Authors is adopted for the correction of compressor steady flow maps.

Today turbocharging represents a key technology to reduce fuel consumption and exhaust emissions for both Spark Ignition and diesel engines, moreover improving performance. 1D models, generally employed to compute the engine-turbocharger matching conditions, can be optimized basing on certain information about turbine and compressor behavior. Because of difficulty in the correct evaluation of turbine isentropic efficiency with direct techniques, turbocharger turbine efficiency is generally referred to thermomechanical efficiency. To this aim, the possibility to accurately estimate power losses in turbocharger bearings can allow the assessment of the turbine isentropic efficiency starting from the thermomechanical one. In the paper, an experimental and theoretical study on turbocharger mechanical losses is presented. The proposed model, developed in the MATLAB environment, refers to radial and axial bearings.