3-D COMPUTATIONAL LOSS ANALYSIS OF AN ASYMMETRIC VOLUTE TWIN-SCROLL TURBOCHARGER

摘要

In times of stringent emission standards for automotive and truck applications, exhaust gas recirculation (EGR) is used in IC engines to reduce NO_x emissions by recirculating a portion of an engine's exhaust gas. The amount of exhaust gas determined for EGR is withdrawn from the exhaust gas route and routed back into the combustion chamber. The recirculated exhaust gas acts as an inert gas and, when mixed with the pre-combustion mixture, helps to decrease the combustion temperature and thus NO_x emissions. Designed for a diesel engine within a truck application, the turbine in this particular research project is fed by two cylinder groups, however, only the exhaust gas of one group is recirculated. The reduced mass flow in the small turbine scroll (EGR-scroll) through EGR withdrawal, along with the increased pressure required for EGR transport, leads to a massive reduction in the mass flow parameter of the EGR-scroll. The common turbocharger design process has been based on steady admission rather than unsteady admission given through the pulsating nature of multi-cylinder admission. This has lead to diverging results of turbochargers performing well on steady hot gas test rigs compared to performing badly in the final tests on the engine itself. In this paper however, unequal admission resulting from pulsating admission is taken into account. Based on unsteady admission, a methodology is proposed for steady computations with unequal admissions, and a thorough 3D CFD loss analysis is to be presented to understand the turbine behaviour, reveal the regions for improvements, and provide a framework for further development.