Improved Surge Predictions for a Turbocharger Compression System

To address the growing concerns of greenhouse gas emissions, automotive manufacturers are improving the fuel conversion efficiency of their engines by downsizing and turbocharging them. However, the low flow instability phenomenon known as surge, exhibited by the compression system of a turbocharger, limits the fuel economy benefits of a turbocharged engine. A computational model of the unsteady surge behavior, characterized by self-excited oscillations of pressure and flow rate, has been developed for a one-dimensional engine simulation code to predict varying degrees of surge and help the design and development of engines. A compressor map preprocessor extrapolates and interpolates experimental bench measurements to facilitate the predictions of mild and deep surge. The model has been improved by adjusting the compressor map generation algorithm to account for nonuniformities in the flow field of the compressor inlet duct at low velocities. The level of improvement the new model provides is determined by comparing predictions of the stable operating limit and the transition from mild to deep surge with the earlier model and experimental data. The predicted amplitude and time-averaged values of flow rate and pressure in deep and especially mild surge are closer to the experimental observations using the new model. The flow rates at which mild surge oscillations begin, and where they are greatest, are distinctly lower in the new model, locating the operating points closer to the true surge line of the experimental compressor map. While the improvement to deep surge predictions is less pronounced, the time-averaged flow rate and pressure fluctuations still are closer to the experimental results. Hence, demonstrated by a comparison to an earlier model and experimental measurements, the improved predictions of surge from the new model captures better the underlying physics of the undesired and detrimental instability modes. The new model will be incorporated into engine simulation codes to improve their accuracy, thereby facilitating more efficient energy conversion devices to better suit the needs of society.No embargoAcademic Major: Mechanical Engineerin