Measurement of Interstage Losses of a Twostage Turbocharger System in a Turbocharger Test Rig

The paper describes a measurement procedure to measure complete 2-stage turbo systems (TST - Two Stage Turbo) in a turbocharger test rig. The possibility to measure the complete range of operation of the series-sequential mode of the 2-stage system is proven. Also the performance is broken down for the two turbochargers individually; both when operating as a part of the TST system and measured as completely separated individuals. The maps measured individually were then used to calculate a composed TST-map as if there would be no losses between the two stages, and this composed map was compared to the measured TST-map. The difference between these two maps is interpreted as interstage losses when packaging the two turbochargers as closely as is necessary to fit in the car. The breakdown showed that the entire difference is not solely due to losses of total pressure interstage. There are influences due to the secondary flow structures (eddies, vortices, turbulence etc.) from the upstream turbomachine into the downstream turbomachine that affects efficiency and pressure ratio. This can also lead to positive effects such as increased surge margin for the HP-compressor (High Pressure; downstream) since the LP-compressor (Low Pressure; upstream) generates a co-swirl at the HP-compressor inlet. In total an efficiency-decrease of up to 8%-points and the pressure ratio difference of 0.4 were observed.