The analysis of the energetic losses in a combustion engine shows that one-third of the chemical energy is lost as heat through the exhaust gas. Prior investigations have shown that an exhaust-gas driven Organic Rankine cycle (ORC) is suitable for the recovery of some of that energy. One of the essential components in such an ORC is the expansion machine. An investigation of the suitability of a turbine for this application is presented in this conceptual study.The concept is investigated for a heavy-duty truck application and a passenger-car application. On the basis of predefined design points, a thermodynamic analysis is performed to determine a suitable working fluid and the best process parameters.A single-stage partially admitted impulse turbine shows the best performance at tolerable rotational speeds for the resulting thermodynamic boundary conditions. However, the high pressure ratio requires supersonic blade profiles in order to handle high flow velocities and achieve a high efficiency. To cover the part-load and overload operating points as well, a variable partial admission is included to increase the operating range. The concluding performance predictions are made using CFD simulations, computing flow over 360° of the circumference. Circumferential parts of the stator which are not admitted are closed by walls to simulate the loss due to ventilation.Based on the resulting blade design a conceptual design for a prototype is presented. Different possibilities for bearings and seals are discussed. A CAD model is presented of a prototype of realistic size and weight.