A New Partial Admission Method for Turbocharger Turbine Control at Off-Design

Abstract

A new method for turbocharger control in automotive applications is presented. It is called MEDUSA (Multiple Exhaust DUct with Source Adjustment, European patent application number: 21326 - EP) and is a partial admission system consisting of several separate flow channels that connect the exhaust duct of the engine and individual nozzle segments of the turbine. By opening or closing the individual flow channels using external valves, the turbine flow can be adjusted, hence allowing the whole turbocharger to be controlled. Due to the use of external valves, the system is considerably more robust than other variable geometry systems based on variable inlet guide vanes and thus becomes suitable for application to spark-ignition motors at high temperature. The paper presents a theoretical assessment of this innovative control system, based on one dimensional considerations and CFD simulations. The CFD-calculations of the MEDUSA-system are compared to those of a turbocharger turbine controlled with a variable inlet nozzle. The results indicate that the performance and operating range of the new system is comparable, or even better, than the currently used variable nozzle systems, especially at low load conditions. This indicates that further experimental work is justified as it could become considerably more effective than the typical waste gate systems used in spark ignition engines and provides a new solution for the turbocharger control in these applications. So far, only radial turbines have been considered for application of this method but it could also be used for mixed-flow or axial turbines.