Experimental Evaluation of Active Flow Control Mixed-Flow Turbine for Automotive Turbocharger Application

In the current paper we introduce an innovative new concept in turbochargers—that of using active control at the turbine inlet with the aim of harnessing the highly dynamic exhaust gas pulse energy emanating at high frequency from an internal combustion engine, in order to increase the engine power output and reduce its exhaust emissions. Driven by the need to comply to increasingly strict emissions regulations as well as continually striving for better overall performance, the active control turbocharger is intended to provide a significant improvement over the current state of the art in turbocharging: the Variable Geometry Turbocharger (VGT). The technology consists of a system and method of operation, which regulate the inlet area to a turbocharger inlet, according to each period of engine exhaust gas pulse pressure fluctuation, thereby actively adapting to the characteristics of the high frequency, highly dynamic flow, thus taking advantage of the highly dynamic energy levels existent through each pulse, which the current systems do not take advantage of. In the Active (Flow) Control Turbocharger (ACT) the nozzle is able to adjust the inlet area at the throat of the turbine inlet casing through optimum amplitudes, at variable out-of-phase conditions and at the same frequency as that of the incoming exhaust stream pulses. Thus, the ACT makes better use of the exhaust gas energy of the engine than a conventional VGT. The technology addresses, therefore, for the first time the fundamental problem of the poor generic engine-turbocharger match, since all current state of the art systems in turbocharging are still passive receivers of this highly dynamic flow without being able to provide optimum turbine inlet geometry through each exhaust gas pulse period. The numerical simulation and experimental work presented in this paper concentrates on the potential gain in turbine expansion ratio and eventual power output as well as the corresponding effects on efficiency as a result of operating the turbocharger in its active control mode compared to its operation as a standard VGT.