The development of a pulse-optimized flow control method for turbocharger turbine performance improvement

Abstract

A new turbocharger turbine concept that enhances exhaust energy recovery has been developed; it is known as the ‘rotating vane turbine’ (RVT). It aims to address the negative impact of the pulsating exhaust flow on the turbocharger turbine, so that the exhaust energy can be recovered more efficiently compared to the state of art turbocharging technologies. Different from traditional turbine configurations, in which the nozzle is stationary, the RVT incorporates a rotating nozzle ring at a relatively low speed. It thus minimises the deviation of the turbine incidence angle from the optimal design angle on average through a pulse cycle, it as such leads to an improvement of turbine performance. Two control methods are investigated for the rotating nozzle: a passive self-rotation and one that is controlled from the outside with the use of an external driving turbine. The geometry of the rotating nozzle ring is also optimized to reduce the incidence loss on the nozzle blade under unsteady flow. The new RVT is studied through numerical calculation in order to demonstrate that the rotating nozzle ring can adaptively change the flow angle at the turbine inlet through a pulse cycle. As a result, the turbine operating point is pushed to better performance region with higher turbine efficiency and lower pressure ratio, compared to a traditional stationary nozzle ring. The flow analysis shows that the turbine performance improvement is due to the reduction of the flow separation on the turbine blade under sub-optimal operating conditions. Detailed experimental testing is also carried out to further validate the new concept. Two rotating nozzles with different angles are tested under different flow frequencies, turbine speeds, turbine loads and mass flow rates. As comparisons, stationary vane turbine (SVT) and nozzleless turbine are also tested under the same operating conditions as for RVT. The testing results demonstrate that, the rotating nozzle ring can reduce the amplitude of the flow pulses, thereby reducing the unsteadiness level of the turbine operation. Similar to the simulation results, a significant increase in average turbine efficiency as well as a reduction of turbine pressure ratio are observed for RVT, compared to for SVT or nozzleless turbine. A preliminary study of 1D engine simulation is also carried out to investigate the impact of the new RVT on the engine performance. The simulation results show that, the back pressure of the engine with RVT is reduced based on the same engine power output. This indicates the new RVT can effectively reduce the BSFC of an engine, compared to a traditional SVT.