Abstract
The optimal turbocharger centrifugal compressor wheel design is unique to each application. Parameters such as blade geometry, wheel diameter, and wheel speed, all affect the operating range and efficiency of air compression. In selecting these parameters, the goal is to optimize efficiency at a given set of operating points while providing sufficient margin to surge and choke, quantified on a compressor map. The test benches used to collect data for turbocharger compressor maps are designed to have straight inlets to stabilize air before the compressor. However, the on-vehicle air inlet duct varies widely between applications due to unique underhood packaging constraints. It is common that the on-vehicle duct leading to the compressor inlet is a 90° bend, as air is routed from an air filter to a compressor inlet. This paper explores the different effects a straight and 90° air inlet have on centrifugal compressor performance. Empirical results show the 90° angled compressor inlet on-engine shifts the surge line to lower mass flows by up to 23%, while maintaining similar wheel speed and choke lines. This improvement in surge margin may enable a larger diameter compressor wheel or improved low end torque performance for the same compressor wheel diameter. Peak efficiency also reduces by as much as 4%-points due to non-uniform compressor inlet velocity. Taking these effects into account may lead to a different optimal compressor wheel design for each powertrain application.
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