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.
Automotive turbochargers play an important role in improving fuel economy, reducing emissions and improving drivability. Key to the improvement of the turbocharger performance is compressor efficiency. Compressors used in turbochargers are typically operated in a wide range of speed and flow. This wide operating range is a challenge to the design and improving the performance is often a fine balance between required efficiencies towards the surge, choke regions apart from having a comfortable speed margin for high altitude operations. In this study an existing compressor that best matched a 180hp commercial diesel engine application is chosen and its performance is further improved towards the lower flow region. Improvement is carried out through a set of designed experiments using a combination of Preliminary Design (PD) and Computational Fluid Dynamics (CFD) tools. Mechanical integrity of the wheel is ensured using Finite Element Analysis. A prototype is made out of the improved design and tested in an in-house gas stand. Predicted efficiency improvements are reflected in gas stand tests. Efficiency improvements in the lower flow range are observed over 7% while there is an acceptable drop (3.7%) near the peak power side. The improved compressor also shows higher part load efficiencies.
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