SUPERSONIC IMPULSE TURBINE FOR AUTOMOTIVE WASTE HEAT RECOVERY: A COMPARISON OF THREE DESIGNS OF TURBINE BLADE PROFILES

One current approach considered by automobile manufacturers to recover waste heat uses Organic Rankine Cycles (ORC) to increase the efficiency of combustion engines. However the efficiency of these ORCs is strongly dependent on the efficiency of a suitable expansion machine. For a suitable choice, three different turbines are compared, which are designed for a predefined operating point of such an automobile ORC. These turbines are partially admitted impulse turbines with a trapezoidal Laval nozzle, a circular Laval nozzle and a trapezoidal Laval nozzle with a small expansion ratio in the divergent nozzle part. The scope of this comparison is the performance of the turbines at full and partial admission. To this end, the full admission turbines are numerically investigated with CFD and the losses due to partial admission are considered by an empirical approach. Finally, the losses due to partial admission are shown separately and their main sensitivities are identified.