Radial Expander Design for an Engine Organic Rankine Cycle Waste Heat Recovery System

Abstract It is commonly accepted that waste heat recovery technologies are significant contenders in future powertrain thermal management to further minimize fuel consumption and CO 2 emissions. Organic Rankine Cycle (ORC) systems are currently regarded as amongst the most potent candidates in recovering engine exhaust energy and converting it to electrical power. Crucial areas for the maximization of the efficiency of the ORC system are the appropriate selection of working fluid and the optimization of the expander design. In this study, a novel design methodology of a radial turbine expander for a heavy duty engine ORC waste heat recovery system is presented. The preliminary design of the radial turbine expander includes the development and utilization of an in-house 0/1D code that can be coupled with various organic fluids properties for the calculation of the basic expander geometry. The initial mean-line model for a 200kW-class Diesel engine application investigated produced a solution for a 20kW turbine with 73% isentropic efficiency. The preliminarily optimized expander geometry was used as an input in a detailed CFD code to further optimize rotor geometry. The rotor geometric optimization showed that by increasing exit tip radius by 10% and adopting a 54° back-swept blade design, the maximum isentropic efficiency achieved can exceed 83%.