Centrifugal compressor performance at low mass flow rates has become an issue in the latest years due to engine downsizing and the increase of low-end torque request. The principal drawback of this operating region is the appearance of the surge phenomenon, which is strongly affected by the compressor inlet geometry. This work is addressed to study the impact of different inlet geometries on the compressor performance, including compressor efficiency, noise emission and surge margin. An engine test bench is set up with a centrifugal compressor and both steady and transient (tip-out) tests are performed in order to obtain a complete view of the influence of each configuration. The results show a clear sensitivity of the compressor parameters to the variations of the geometry upstream the compressor inlet.

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Zero-dimensional/one-dimensional computational fluid dynamics codes are used to simulate the performance of complete internal combustion engines. In such codes, the operation of a turbocharger compressor is usually addressed employing its performance map. However, simulation of engine transients may drive the compressor to work at operating conditions outside the region provided by the manufacturer map. Therefore, a method is required to extrapolate the performance map to extended off-design conditions. This work examines several extrapolating methods at the different off-design regions, namely, low-pressure ratio zone, low-speed zone and high-speed zone. The accuracy of the methods is assessed with the aid of compressor extreme off-design measurements. In this way, the best method is selected for each region and the manufacturer map is used in design conditions, resulting in a zonal extrapolating approach aiming to preserve accuracy. The transitions between extrapolated zones are corrected, avoiding discontinuities and instabilities.

Bulk flow condensation caused by the mixing of air streams at different temperatures and humidities is a thermodynamic process that requires strong assumptions to be calculated with low computational effort. The applicability of a model that correctly predicts this phenomenon has grown recently due in part to the deployment of the Long Route Exhaust Gas Recirculation emission reduction technique in combustion engines and the damage to the turbocharger caused by the condensation produced when the intake air is mixed with the combustion gases. This work is addressed to expose a condensation model that is implemented in a commercial 3D-CFD code and is then verified, checking whether the implemented physical equations are behaving as intended. Finally, a practical application is made, showing the potential of model to predict water condensation in a LR-EGR T-joint.

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