Turboelectric distributed propulsion system design and tank sizing for novel hydrogen-fuelled aircraft: a mission-level analysis

Abstract

In an ever-growing civil aviation industry, the need to reduce the related carbon footprint is more relevant than ever. One way to substantially contribute to this cause is to use liquid hydrogen (LH₂) as a fuel, which would allow for zero in-flight CO₂ emissions. However, there are major challenges associated with its implementation, both from the perspective of the airframe design as well as the propulsion and fuel system architecture. This research contributes to knowledge by addressing the sizing of the LH₂ aircraft components from a mission level perspective. More specifically two novel aspects are addressed based on that philosophy: LH2 tank sizing with gaseous hydrogen (GH₂) extraction for pressure control and design space exploration of turboelectric distributed propulsion (TeDP) and partially TeDP configurations powered by LH₂. This is achieved through a developed framework that enables the assessment of a hydrogen aircraft and its subsystems at mission level. It comprises four co-dependent modules: aircraft performance, aircraft weight estimation, LH₂ tank sizing and propulsion system performance and weight estimation. For each one of the modules, novel and existing methodologies, from kerosene applications, are combined to address the sizing of the components of the LH₂ aircraft. The research then focuses on a case study of a blended-wing body architecture that is based on NASA’s N3-X and is powered by a TeDP system. The airframe is scaled to accommodate more passengers as well as allow for enough volume to fit large enough LH₂ tanks that would enable the aircraft to meet design mission requirements. Based on the available airframe volume, two sizing philosophies are considered: one where only LH₂ is used for the engines and another where both LH₂ and GH₂ are used to restrain the pressure increase of the tank during the cruise segment. Compared to the first application, the second showcased both significant weight savings as well as increased fuel capacity for the same external volume occupied. Finally, for the propulsion system, a design space exploration is performed to identify optimum propulsion design parameters for turboelectric and partially turboelectric distributed propulsion configurations. The different design options are analysed based on efficiency, weight and mission level fuel economy on the design mission and it is demonstrated that higher specific thrust designs are more suitable for the LH₂-powered long-range application presented. The optimum configuration identified consists of two low by-pass ratio turbofans that are buried in the wing roots and power 12 fans installed over the aft section of the fuselage.