The 6-inlet Single Stage Axial Turbine Concept for Pulse-Turbocharging: A Numerical Investigation 2019-01-0323
The demand for high-efficiency engines has never been greater as energy consumption and emission reductions are key components for continued competitiveness in today’s transportation industry. A main contributor to recent and future improvement of the internal combustion engine is the gas exchange process. By utilizing the exhaust energy in the turbine stage of an exhaust turbocharger, the pumping work can be improved resulting in significant gains of engine system efficiency. Two main aspects can be identified with regards to the turbine design that are crucial: The level of exhaust pulse separation and turbine efficiency at high pressure ratios. For a pulse-turbocharged engine both aspects need to be considered in order to gain full benefit of the exhaust energy utilization process.
In this study, a novel axial turbine stage concept with divided inlets is considered. The turbine stage is part of a prototype turbocharger for a performance-optimized Scania 13 liter heavy-duty diesel engine with focus on exhaust energy utilization. The concept design makes it possible to combine both high efficiency levels and pulse separation.
At “on-engine” operation, the turbine stage will operate at varying conditions, alternating between different states of admission. Key to the success of the concept is the turbine performance as a function of admission ratio. By an extensive numerical 3D CFD simulation, overall turbine parameters, performance and detailed flow visualizations have been evaluated. As a final step, the turbine “on-engine” operation and performance was studied using unsteady time-dependent boundary conditions from engine simulations. The study provides key insight into to the complex nature of the flow in the turbine stage, operating state as well as quantifying the turbine performance. This kind of detailed evaluations is needed for successfully developing the axial turbine with divided inlets for the turbocharger application.