This paper presents an integrated assessment of liquid hydrogen as an aviation energy carrier, covering fuel production, aircraft performance, and fleet-level climate impacts. The results, based on the H2Avia research project, indicate substantial potential for reducing life-cycle global warming impacts compared to conventional kerosene. The analyses conducted for the interdisciplinary assessment are presented. The analysis shows that the use of liquid hydrogen eliminates CO₂ emissions during fuel burn, resulting in a significant reduction in global warming potential compared to conventional kerosene, despite remaining upstream emissions from production and transport. The aircraft application cases and the applied technologies assessment scenario are described. The modeled technologies essential for the hydrogen aircraft are discussed, and exemplary values are given. Integrated overall aircraft performance results are given and discussed. At the aircraft level, hydrogen-based aircraft require an 8–18% increase in design mission block energy compared to a 2040 kerosene baseline yet still achieve a reduction in effective global warming potential of 55–86% comparing a representative pair route between Europe and North America (6730 km). An overview of the fleet modeling approach and the applied scenarios is given. For a scenario with energy cost and climate impact as equally weighted minimization goals, the global fleet analysis yields a global warming potential reduction of 60% compared to the non-liquid hydrogen baseline scenario. Overall, the results suggest that liquid hydrogen-powered aircraft can deliver significant mission- and fleet-level reductions in global warming potential and thus represent a promising pathway for achieving long-term aviation climate targets.

Novel aircraft propulsion concepts based on electrochemical conversion technologies, such as solid oxide fuel cells (SOFCs), are being investigated to enable climate-neutral air transport. It is crucial to identify SOFC architectures that are relevant and capable of fulfilling the specific requirements for aerospace applications, i.e., optimization for mass and volume. For a mature design and performance synthesis of propulsion system concepts, including highly integrated SOFCs, more sophisticated component models are necessary for a clean and unified integration of SOFC technology. The models should include both electrochemical performance and sizing, as well as system integration, already at the early stages of system design and analysis. This work presents a MATLAB-based 0D approach within the Bauhaus Luftfahrt Aircraft Propulsion System Simulation (APSS) framework to model the steady-state operational characteristics of an SOFC stack and determine its preliminary size. The results serve as a basis to assess integration aspects and challenges for various SOFC architectures, such as planar or microtubular arrangements. For simulated fuel cell stacks, validation studies are performed to ensure realistic dimensioning, as well as selected analyses showing the sensitivity of the model and resulting stack size to relevant operating parameters, such as temperature or required power. The studies presented within this work are an important step towards enabling the design and subsequent evaluation of overall fuel cell-driven propulsion system concepts.

The design of hybrid electric propulsion (HEP) systems involves multiple sizing requirements and operating conditions that affect aircraft performance. Assessing their overall potential requires the coupled consideration of hybridization, battery technology, mission utilization and operational constraints. Therefore, an integrated methodology combining HEP sizing with simplified aircraft design and performance methods is presented. A parallel HEP concept with an electrically assisted compressor is investigated for a 50 PAX regional aircraft and a 19 PAX helicopter, considering an Entry-Into-Service (EIS) in Y2035+. To enable operation without electrical assistance, gas turbine oversizing is applied. This comes with mass and efficiency penalties but significantly expands the operational hybridization range. At a battery system specific energy of 500 Wh/kg, the regional aircraft achieves a 1% block fuel reduction on the design mission (400 nmi), compared with a 22% reduction on the shorter typical mission (150 nmi) through increased battery utilization. For the helicopter, block fuel increases by 11% on the design mission, but decreases by 10% on the typical mission. The results demonstrate that aircraft utilization is a key factor for the sizing and assessment of parallel HEP systems.