EXPERIMENTAL SETUP OF A SMALL SUPERSONIC TURBINE FOR AN AUTOMOBILE ORC APPLICATION RUNNING WITH ETHANOL

asme-orc2015 Tracking Number 172

A significant part of the global emissions of greenhouse gases is caused by road traffic. Therefore, automobile manufacturers are in search of opportunities to decrease these emissions by increasing the efficiency of combustion engines. The analysis of the energy flows in such combustion engines showed that a considerable part of the inserted chemical energy is lost as thermal energy in the exhaust gas. Prior investigations have shown that an Organic Rankine Cycle (ORC) is convenient to recover some of this energy. Within these ORCs, ethanol promises to be a suitable working fluid for this application. But the efficiency of the whole ORC is significantly dependent on the efficiency of the expansion machine. On this account, it is necessary to develop suitable expansion machines for such ORCs. At the Institute of Turbomachinery and Fluid Dynamics (TFD) an axial turbine was developed to prove that an efficient operation is possible. But the boundary conditions are quite challenging for a turbine. Firstly, the ORC requests a high pressure ratio to maximize the power output. Secondly, the small amount of thermal energy in the exhaust gas causes low mass flows. The single stage design promises a compact prototype and reduced manufacturing costs. But this also leads to a supersonic flow velocity in the turbine. Special blade shapes are used to achieve an efficient operation of the turbine. Additionally, the small mass flows cause a small turbine diameter and a very high rotational speed. The target, a compact expansion machine, requires the mounting of the turbine rotor and the generator rotor on one shaft. This requires the utilization of a high speed generator, which can handle the rotational speed. The prototype of such a machine was manufactured at the TFD for an experimental investigation. Firstly, the experiments shall confirm that a turbine is suitable for the automobile ORC-application and achieves the predicted performance. Secondly, the feasibility of the turbine-generator design should be demonstrated. The experiments will be performed at a test bench of the University Hannover. This test bench is able to provide vaporous ethanol at the requested pressure level, for a safe operation of the expansion machine. The poster gives an overview of the planned experiments and the setup. This contains detailed description of the prototype itself. The accurate measurement of the operation conditions is challenging, because several loss mechanisms occur. Therefore several measurement points are implemented to get an accurate measurement of the operation of the expansion machine. In addition, several ancillary units are necessary for running the test bench. This includes a power electronic for high speed generators, a water conditioning system and the steam producing unit.