Oil sealing in a turbocharger is a key design challenge. Under certain engine operating conditions oil in the lubrication system is likely to enter the compressor or turbine wheel crossing the piston rings which are used to arrest the undesirable oil flow. Compressor side oil leakage can cause white smoke and particulate emissions. Limited experimental and analytical methods are available to aid the designers in developing the oil flow path. The oil flow path has dimensions of the order of a few microns in certain areas and in mm in other areas. In addition, the flow is comprised of oil and exhaust gas mixture in certain regions. The combined effects of disparate geometric length scales and two-phase flow adds to the complexity of the flow. Understanding the oil flow allows the designer to correctly size the components, flow path and also specify the appropriate clearances between for instance shaft and bearing journals. In this study a Computational Fluid Dynamics (CFD) Model has been built and validated through several experiments conducted particularly to check the oil leak through the piston rings. The study shows that CFD based models can predict within engineering accuracy the flow through leakages in a turbocharger. The importance of manufacturing tolerances on the leakages is also highlighted.
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