Modelling of a pressure wave supercharger including external exhaust gas recirculation

Abstract

This paper presents a mean value model of a pressure wave supercharger together with a spark ignition engine including external exhaust gas recirculation. The model of the pressure wave supercharger is based on linear one-dimensional gas dynamics. It includes an approach for the mixing zone between exhaust gases and fresh air which permits the calculation of the exhaust gas recirculation rate within the charger. The mass flow of the recirculated exhaust gas is the combined effect of too large an exhaust gas penetration into the cell wheel of the charger and of incomplete scavenging of the cell wheel. The model of the pressure wave supercharger is validated by the identification of four physically based model parameters and shows an error smaller than 5 per cent over the operating range investigated. The model can be integrated into an overall engine system model which predicts transient exhaust gas recirculation effects during load steps with good accuracy. The system model demonstrates that exhaust gas recirculation during transients is mainly caused by incomplete scavenging of the cell wheel and not by the exhaust gas penetration into the cell wheel being too large. Both the model of the pressure wave supercharger and the overall engine system model are validated by steady state and transient measurements on a dynamic test bench.