Numerical investigation of a radial turbine with variable nozzle geometry for fuel cell systems in automotive applications

When using a fuel cell drive in the automotive sector, electrically driven turbochargers are used to increase system pressure and improve efficiency. Due to the operating temperature of the polymer electrolyte membrane fuel cell (PEMFC) and the resulting low exhaust gas temperature, the electric drive is necessary to compensate for the low recuperated turbine power to drive the compressor. Thus, the objective of this article is to investigate the potential of power recovery and efficiency increase when using variable nozzle turbine geometries. In addition, the adjustability of operating points by use of variable geometries is analysed in more detail. For this purpose, numerical setups are developed to use them for stationary preliminary investigations of a radial turbine stage. The results of the investigation are compared to the results of the non-variable turbocharger version. The numerical study shows that the use of variable turbine geometries is also beneficial in PEMFC air supply systems. Furthermore, the use of variable geometries results in better efficiency over a wide operating range.