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

The paper investigates accuracy of performance measurement in two-stage turbocharging systems, due to aero-thermal inter-stage phenomena. A novel methodology to measure performance of turbochargers into equivalent maps has been implemented, for mapping of turbocharging systems in steady turbocharger gas-stands. The comparison of equivalent maps and stand-alone high and low pressure turbochargers maps is performed, via single maps combinations. In this scenario, two-stage system performance are calculated on the basis of single stages variables in a simplified map-based one-dimensional code. In order to quantify the influence of heat transfer in turbochargers on the two-stage turbocharging system, diabatic and adiabatic turbochargers maps with heat corrections for each stage ares implemented. In conclusion, in comparison to equivalent two-stage maps, combined stand-alone maps predict a significantly higher pressure ratio and efficiency at compressors, due to low speed maps extrapolation. Meanwhile, the turbine net efficiency is missed by about 10% at elevated corrected mass flow operations, due to underestimation of swallowing capacity and isentropic expansion in the combined map approach.