Impact of the working fluid in orc-based waste heat recovery systems for turboshaft engines

Waste heat recovery in aircraft engines is a promising solution to enhance their performance and reduce the mission fuel consumption. The combined-cycle turboshaft (CC-Turboshaft) is a concept which features a Brayton cycle with a subsequent organic Rankine-cycle waste heat recovery unit. It is suitable for turbo-electric propulsion as both the organic Rankine-cycle turbine and the turboshaft free power turbine can be connected to electrical generators. The purpose of this study is to investigate the impact of different working fluids of the organic Rankine-cycle unit on the CC-Turboshaft performance. The results suggest that the impact of the organic Rankine-cycle working fluid on the block fuel consumption is approximately Å}0.6% and Å}0.3% of the aircraft total mass, which are considered negligible. This is due to the design constraints of the heat exchangers, which are arguably the most challenging components for this application. The effect of the working fluid is more evident in the generated power, which varies in the order of +-5%.