In recent years, the fuel efficiency of passenger vehicles has been enhanced through engine downsizing by turbocharging. To meet increasingly stricter fuel efficiency regulations, however, turbochargers that have a wider operation range and are highly efficient in comparison with existing ones are strongly required. This paper presents turbine performance analysis and efforts to achieve high performance under exhaust pulsation focusing on the fact that a turbocharger installed on an engine is driven under exhaust pulsation. Through collaborative research with Imperial College, which can measure the unsteady performance of a turbine under exhaust pulsation, and the University of Cambridge, experts in enhancing turbine performance, the flow phenomenon was elucidated by unsteady performance measurement and large-scale flow simulation. It was found that turbine performance under exhaust pulsation cannot be evaluated in a quasi-steady state and has a hysteresis characteristic, and that under a pulsation peak pressure with high exhaust gas energy, the blade leading-edge incidence loss increases excessively. Mitsubishi Heavy Industries, Ltd. utilized these findings for the development of a new mixed-flow turbine and achieved the enhancement of turbine performance under exhaust pulsation.
