Effect of a Map Width Enhancement System on Turbocharger Centrifugal Compressor Performance and Surge Margin

Engine downsizing is potentially one of the most effective strategies being explored to improve fuel economy. A main problem of downsizing using a turbocharger is the small range of stable functioning of the turbocharger centrifugal compressor at high boost pressures. Several stabilization techniques have been studied to increase the compressor operating range without sacrificing the compressor efficiency. This paper presents an experimental study on a turbocharger compressor equipped with casing treatment (a map width enhancement (MWE) system). A KKK turbocharger was modified and tested at Ecole Centrale de Nantes. The experimental program mainly dealt with traditional compressor performance measurements for an MWE. Whereas much work has been previously carried out to study the apparatus communicating between the annular flow passage and the impeller wheel, an apparatus with multiple holes has not been previously considered. In this paper experiments have been inducted to study the effect of an MWE structure with plurality of holes on the performance and stable functioning of a turbocharger centrifugal compressor. The effect of extending the length of the inner tubular wall has also been investigated. Two different MWE configurations have been tested and results were analyzed while conducting a series of tests. The experimental studies have shown that while the MWE was advantageous in increasing pressure ratio at high compressor speeds, it failed in extending the compressor map. Moreover, extending the inner tube length was efficient in significantly shifting the surge line to low flowrates, by producing a uniform flow at inducer inlet.