Optimization of a Hydrogen-based Hybrid Propulsion System Under Aircraft Performance Constraints

This paper addresses the topic of the conceptual design of a regional aircraft with hybrid electric propulsion based on hydrogen fuel cells. It aims at providing an optimization-based method to design a hybrid propulsive system comprising two power sources (jet fuel and hydrogen) for the generation of the required propulsive power and at studying the impact of fuel cell technologies on the aircraft performances. Indeed, by performing optimizations for two hybrid propulsive systems using either low temperature or high temperature Proton-exchange membrane fuel cells, this study provides a preliminary assessment of the impact of the fuel cell operating temperature on the system design and the overall aircraft performance. First, this paper gives a description of the baseline turboprop regional aircraft with a focus on its high speed and low speed flight performances which will serve as requirements for the design of the hybrid aircraft. Then, the hybrid electric architecture and the sizing models of the propulsion system are presented. Finally, optimizations are performed to design two parallel hybrid propulsive systems based on different fuel cells technologies and aimed at minimizing the block fuel per passenger over a mission of 200 nm. Results show how the proposed methodology and models lead to design two propulsive systems capable of reducing the fuel consumption per passenger by more than 30% compared to the baseline aircraft. The study also shows that the choice of fuel cell operating temperature has a first-order impact on the total mass of the propulsive system due to the higher cooling requirement of the low temperature fuel cells.