H. Mohtar

Describing uncertainties encountered during laboratory turbocharger compressor tests

To improve the existing turbocharger compressor technologies (surge margin increase, improving compression abilities, etc.), compressor tests require accurate determination of efficiency, pressure, and exact surge line emplacement. Moreover, due to nonideal measurement conditions typically encountered during turbocharger compressor performance testing, it is imperative to define measurement uncertainties to the experiments. This article deals with how reliable the results of the turbocharger compressor tests for a given test facility are. This article begins with a general introduction to measurement uncertainties, and a description of the turbocharger test facility together with sources of error of the different transducers is then presented. Uncertainty equations are derived from compressor performance relations; transducer errors were introduced to uncertainty equations so that the efficiency, pressure, and mass flow uncertainties of compressor at different functioning points can be predicted before compressor testing. Uncertainty analysis of nine different compressor functioning points was carried out. Finally, parameters that mostly affect the compressor performance results were identified.

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 programme 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 analysed 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.

Effect of Casing Treatment and Variable Axial Guide Vanes on a Turbocharger Compressor Performance

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 were 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 system, MWE) and a variable inlet guide vane system (VIGV). 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 (map width enhancement) structure with multitude of holes linking the annular flow passage and the impeller wheel, four different inner tubular length extensions and imparting positive and negative preswirl using VIGV system. 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. The different inner tubular length extensions have shown no significant effects on surge line improvement for this particular design. Results obtained from MWE system have been compared to those obtained when imparting positive and negative preswirl using an VIGV system.Copyright