Life cycle assessment of an aircraft fuel cell propulsion system

Kurzfassung

As air travel continues to expand, the need for sustainable solutions to mitigate its environmental impact becomes more urgent. In response to this challenge, the European Union's Flightpath 2050 initiative sets ambitious goals, including a 75% reduction in CO2 emissions and a 90% reduction in NOx emissions from commercial aircraft by 20501. To meet these targets, innovative technologies such as fuel cell propulsion systems (FCPS) can play a significant role, particularly for regional flights. However, research on the environmental impacts of FCPS in aviation remains limited, with most studies focusing on hybrid-electric and battery systems for short range aircraft or lightweight all-electric aircraft rather than fuel cells as standalone solutions covering the regional flight distances. This gap highlights the need for a thorough investigation into the life cycle impacts of fuel cell technology in regional aircraft applications. In order to assess the environmental impacts of FCPS with a life cycle assessment (LCA), one FCPS and one passenger kilometre were considered as functional units. The former refers to the production phase of a single FCPS, while the latter encompasses both the production and use phases including the use of hydrogen as a fuel. To carry out the LCA, life cycle inventories (LCI) were generated for all the individual components and sub-components of FCPS. A python-based tool was created that builds upon an existing model for sizing of aircraft fuel cell systems2 based on a particular flight mission. The tool includes equations to compute a thorough mass breakdown of every fuel cell stack component based on the FCPS data obtained from the model. LCIs are automatically generated using background information from the ecoinvent database3 in addition to the masses for the balance of plant (BOP) components. The open source Brightway24 framework is used to do the life cycle impact assessment. For both present and future FCPS, the tool allows for the flexible adaptation of LCIs to different flight scenarios and FCPS applications covered by the model. A detailed description of the assessment tool's approach and advantages will be provided. The environmental footprint of example FCPS systems and passenger flights will be discussed. A 3.12 MW FCPS for a 70-seat regional aircraft designed by Atanasov5 (designed aircraft resembles the size of ATR-72) is assessed to demonstrate the application of the tool. Beyond reducing GHG emission, the assessment covers the potential environmental impact categories for a comprehensive evaluation. The results are analyzed and interpreted by separating the impacts into the production and use phases of the FCPS, identifying key hotspots. The environmental impacts of the FCPS are largely influenced by the production of key fuel cell components, i.e. the bipolar plate and catalyst. The BOP components generally exhibit lower environmental impacts, with the exception of certain categories, such as ozone depletion, where components like the humidifier make a significant contribution. In the use phase, the FCPS itself does not emerge as the primary contributor to environmental impacts. Instead, hydrogen production is the dominant factor, particularly due to the electricity required for hydrogen production, even when renewable energy sources are used. Eventually, the well-to-wheel LCA results are compared to the traditional fossil kerosene aircraft in order to determine the possible trade-offs between the reduced global warming potential and other environmental impacts.