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Surge occurrence in automotive engine turbochargers is known to be dependent on the installation conditions. It is proven that the flow pattern produced by the inlet ducting at the compressor inducer modifies surge margin. But also the engine intake line acoustics, both compressor upstream and downstream, affects turbocharger surge. In the paper the effect of different parameters in the intake line geometry on compressor surge is investigated. Modifications in the air filter volume, compressor inlet geometry and compressor outlet length have been considered. Surge limit obtained on a steady gas-stand is compared to those measured on the engine test bench using two different methodologies. Testing results show significant differences in term of surge line shift and the corresponding engine low end torque. A 1D model of the engine has been built using a non-steady compressor model able to predict surge occurrence.

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.