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This work presents a study to characterize and quantify the mechanical losses in small automotive turbocharging systems. An experimental methodology to obtain the losses in the power transmission between the turbine and the compressor is presented. The experimental methodology is used during a measurement campaign of three different automotive turbochargers for petrol and diesel engines with displacements ranging from 1.2 l to 2.0 l and the results are presented. With this experimental data, a fast computational model is fitted and used to predict the behaviour of mechanical losses during stationary and pulsating flow conditions, showing good agreement with the experimental results. During pulsating flow conditions, the delay between compressor and turbine makes the mechanical efficiency fluctuate. These fluctuations are shown to be critical in order to predict the turbocharger behaviour.

Surge phenomenon is becoming a limitation of the low end torque for downsized turbocharged Diesel engines. The stable operation of centrifugal compressors is limited at low flow rates because of the occurrence of surge. In the present work a CFD analysis of the flow inside automotive centrifugal compressors near the surge line is carried out. For this purpose, the actual geometry of a compressor -including its inducer, rotor, diffuser and volute- has been modelled with a CFD code. Initially, steady calculations have been performed to have a first approximation of the flow characteristics inside the compressor. In these calculations, a source term is imposed in the momentum equations to simulate the movement of the rotor and its effects on the air when it passes through it.