Life Cycle Assessment of Fuel Cell Propulsion Systems for Regional Aircraft

Kurzfassung

With the EU's aim to become climate neural by 2050, drastic greenhouse gas (GHG) emission reductions will be required in the transport sector. In aviation there are generally two options for GHG emission reductions: sustainable aviation fuels or innovative propulsion systems utilising renewable power or hydrogen. Fuel cell propulsion systems (FCPS) pose a promising alternative, especially for regional level flights with smaller aircraft. However, so far very limited research has been conducted about the environmental impacts of fuel cells in aircraft applications and none has focussed on fuel cells only as opposed to hybrid-electric propulsion or hydrogen combustion. In order to assess the environmental impacts of FCPS with a life cycle assessment (LCA), life cycle inventories need to be created for the different FCPS parts. A python-based tool was developed that builds upon a previously established model for sizing of aircraft fuel cell systems in dependence of a specific flight phase/mission. The tool encompasses equations to calculate a detailed mass break-down of all fuel cell stack components based on the overall stack mass received from the model. Together with the masses for the balance of plant components, life cycle inventories are automatically created with background data from the ecoinvent database. The life cycle impact assessment is conducted with the open source framework Brightway2 . The tool enables flexible adjustment of the life cycle inventories to various flight scenarios and fuel cell system applications covered by the model for current and future FCPS. The methodology and the benefits of using the assessment tool will be described in detail. An exemplary 3.12 MW FCPS for a 70 seat aircraft is assessed to demonstrate the application of the tool. The LCA is performed for both a functional unit of one FCPS and one passenger kilometre where the latter then also includes the provision of hydrogen. The assessment includes any possible critical environmental impact category for a holistic assessment, even beyond GHG emission reduction. Preliminary results suggest that the major contributors to most environmental impacts of the FCPS are the catalyst and bipolar plates in the fuel cell and the hydrogen tank as part of the balance of plant. However, when the whole life cycle from well-to-wheel is considered in one passenger kilometre, hydrogen production, even from renewable resources, still overshadows any other environmental impact contribution. The well-to-wheel LCA results are compared to the fossil fuel reference kerosene propulsion in order to identify potential trade-offs of reduced global warming potential with other environmental impacts.