Exergy assessment comparison of conventional and hybrid-electric aircraft propulsion systems

The purpose of this research is to develop an exergy-based method to evaluate and compare different aircraft propulsion systems architectures to assist the design engineer at the early stages of product development. The method was successfully applied to a case study comprised of a baseline regional aircraft powered by gas turbines, which was compared to a hybrid-electric propulsion (HEP) version comprised of the gas turbines hybridized with batteries. The highest exergy efficiency of 33.5% was obtained for a configuration that presented a 5% degree of hybridization (DOH), defined as “power coming from batteries divided by total power”, and 800Wh/kg battery density. This corresponds to an increase of 0.7% when compared to the 32.8% efficiency of the baseline gas turbine. On the other hand, the aircraft total weight increased 2,160 kg, or 7.1%. Also, both the exergy consumption and exergy destruction increased with hybridization. For the flight mission, a remarkable increase of 2% to 7% was obtained for these parameters, as hybridization increased from 5% to 15%. On top of that, the HEP configuration saves 23 kg of jet fuel or 1% of fuel burn along the mission in comparison with the baseline. CO \(_{2}\) $_2^{}$ emissions reduction was around 70 kg per flight mission, as expected, since emissions increase proportionately with fuel consumption. Exergy-based emission costs and exergy destroyed in the kerosene refinery plant and in the electric power generation plant were also evaluated. Finally, some possible means to re-use the exergy lost in the aircraft propulsion system were presented and discussed.