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One solution for reducing the nitrogen oxide emissions of diesel engines is the Low-Pressure-Exhaust-Gas-Recirculation method. This solution involves gathering exhaust gas from behind the turbine and mixing it with the aspirated fresh air upstream of the turbocharger compressor. This in turn tends to result in an inhomogeneous inflow into the compressor affecting the distribution of the velocity, the total pressure and the total temperature. The efficiency of the centrifugal compressor is influenced by this strongly disturbed inflow. In this paper the consequences of different mixer geometries developed for this application are examined. Experimental investigations are carried out in order to understand the flow processes of the disturbed inlet-flow structure and the associated effects on the efficiency of the compressor. These different mixer geometries are investigated for different mass flow ratios. These inflow conditions are then compared to a straight, undisturbed inflow and an elbow inlet. The aim is to decide which one of these mixing geometries is most appropriate.

In this paper, numerical results of the mixing behavior of two mass flows having different temperatures in an elbow, which is located upstream of a turbocharger compressor, are presented. The background for these investigations are the thermal problems and the problems due to droplet impacts, which arise as a result of Low Pressure Exhaust Gas Recirculation for a turbocharger compressor. In these investigations, the temperature distributions resulting at the inlet of the compressor are mainly of interest. Of further interest are the trajectories of possibly arising water droplets in the inflow of the turbocharger compressor. In the first step different injection configurations are calculated without the compressor in order to get a first impression of the mixing behavior of two mass flows in an elbow. Afterwards three of the injection geometries are calculated including the compressor to see the influence of the compressor on the mixing behavior. The results show a strong influence of the direction of the injection and of the relative position of the injection to the elbow unit. Subsequently, visualization tests are made to qualitatively check the mixing behavior of the different elbow geometries.

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