Fuel Cell Systems (FCS) for different aircraft concepts: Life cycle assessment

Kurzfassung

The decarbonization of aviation is a critical component of global efforts to mitigate climate change. The aviation sector primarily relies on two options for the climate impact reduction: Sustainable Aviation Fuel (SAF) and novel propulsion technologies. Among these emerging technologies, hydrogen-powered fuel cells represent a promising pathway toward achieving low-emission flight compared to conventional aircraft technologies. Assessing the environmental impacts of this technology is imperative to guide technology development and compare with conventional systems. This study presents the Life Cycle Assessment (LCA) of a fuel cell system (FCS) for two liquid hydrogen-powered aircraft concepts: (1) a 70-seat regional aircraft utilizing a 3.12 MW fully fuel cell-based propulsion system (manuscript submitted to a peerreviewed journal), and (2) a 250-seat mild hybrid electric propulsion (MHEP) aircraft employing hydrogen combustion in turbofan engines, supported by a 1.4 MW fuel cellbased auxiliary power unit (APU). While the focus on the first concept stems from its potential as the pioneering commercial aircraft to utilize hydrogen fuel cell technology, the second concept is being explored as a more immediate pathway for gradual decarbonization; since the development of the first concept is unlikely to materialize in the near future. The LCA is performed for both a functional unit of one FCS and one passenger kilometer (pkm). An automated Life Cycle Inventory (LCI) is created by developing a pythonbased tool which builds upon a previously established model for the sizing of aircraft fuel cell systems. The tool incorporates the calculation of mass breakdown of the fuel cell stack which is eventually combined with the mass data of BOP (Balance-of-Plant) components to acquire the full LCI data of an FCS system, where the ecoinvent database was used as the background data source. The tool enables the LCI generation based on various fuel cell types and flight missions through flexible data adjustment. The life cycle impact assessment was conducted with the open source framework Brightway2. The tool is implemented in evaluating the aircraft concepts discussed earlier. Considering the production of 1 FCS unit, the main contributors to the environmental impact are catalyst and bipolar plates. However, in the operational phase, the supply chain for liquid hydrogen production contributes the most. A simplified comparison of the 70-seater fuel cell aircraft with the one powered by fossil kerosene and eSAF is also provided, where the fuel cell aircraft exhibits better environmental performance in the majority of the impact categories. While the fuel cell-only aircraft offers superior environmental performance in terms of in-flight emissions, its practical implementation is challenged by current technological maturity and hydrogen infrastructure limitations. Meanwhile, the hybrid configuration featuring a fuel cell APU provides a more feasible short-term solution. Although the fuel cell-based propulsion system is not yet developed, the present study illustrates that gradual decarbonization can already begin through the use of a fuel cell-based APU. It enables the aviation sector to gain operational experience with hydrogen and fuel cell technologies, reduce emissions from conventional APUs, and begin developing the necessary ground infrastructure for future development of the fuel cell aircraft in full swing.