Effect of inter-stage phenomena on the performance prediction of two-stage turbocharging systems

The paper analyses the influence of aero-thermal inter-stage phenomena on the performance prediction of two-stage sequential turbocharging systems. A novel methodology to measure performance of two-stage turbocharging systems into equivalent maps has been implemented and detailed. Investigation of a two-stage sequential turbocharging system has been performed in a steady turbocharger gas-stand, obtaining thermodynamic properties of the complete turbocharging system. The measurement of equivalent maps and the combination of stand-alone HP and LP turbochargers maps have led to the quantification of inter-stage effects and the influence on performance predictions of the two-stage systems.
In this study, equivalent two-stage and combined HP and LP stand-alone maps are compared in order to quantify the variation of performance affecting the two-stage system. Specifically, a simplified 1D model of the two-stage system flow path is developed for the investigation. In order to quantify the influence of inter-stage effects, heat correction of the diabatic compressor and turbine maps has been implemented. In conclusion, in comparison to equivalent two-stage maps, combined stand-alone maps predict a significantly higher pressure ratio and efficiency for the compressor system at conditions of low equivalent speed, while the turbine net efficiency is missed by about 10% at elevated corrected mass flow operations.