Study of externally waste-gated turbine performance under steady and pulsating inlet conditions for improved turbocharger matching

摘要

The demand for drastic reduction in CO2 emission among road vehicles has seen downsizing becoming a megatrend in modern engine developments due to its benefits in reducing throttling loss and improvement in engine efficiency. In light of this, turbocharging is seen as one of the key enabling technologies and therefore carries along with it an ever-increasing challenge in terms of system-matching as the device is required to operate in ranges never encountered before. The increasing reliance on 1-D engine performance simulation tools calls for more accurate representation of the turbocharger model. The present study assessed the turbocharger turbine maps for use in commercial 1-D gas dynamics engine code from several aspects, namely the width of the map and the representation of turbine unsteady performance in the virtual environment. Furthermore, the present work assessed the performance of turbine under waste-gated operations. For this, an experimental work has been carried out on a bespoke waste-gated turbine layout over a wide range of operating conditions. The performance of the radial turbine under steady inlet conditions was evaluated for different waste-gate openings, at various points along several speed-lines. Then the unsteady tests saw the turbine performance evaluated at various sets of pulse frequencies, turbine loadings and waste-gate openings. Analysis of this study include the impact of turbine map width on the turbine performance modelling in a commercial 1-D gas dynamics engine simulation software and subsequently the prediction of the engine’s performance. This simulation work is carried out based on an actual heavily downsized gasoline engine with a series super-turbocharging system. The study also examined the method of incorporating the effects of turbine unsteady performance under waste-gated and non-waste-gated conditions in the performance maps used in 1-D code and evaluate its impact on the engine performance prediction. The outcome of the study aims at providing a deeper understanding on the unsteady performance of a turbocharger turbine which will lead to improved turbocharger-engine matching methods in the future.