This paper investigates green hydrogen and bio-based sustainable aviation fuels, including their production technology and feedstock, in combination with Clean Sky 2 propulsion technologies and novel hydrogen-powered propulsion technologies. The impact that these alternative aviation fuels and propulsion technologies can have on greenhouse gas emissions is identified and the demand for alternative aviation fuels is compared with their expected availability, both until 2050.

The TRANSCEND project (as part of the Clean Sky 2 Technology Evaluator) aims to develop roadmaps for full scale entry-into-service of selected propulsion technologies and alternative fuels in the period 2035-2050, in line the emission target of FlightPath-2050 for the period 2035-2050. In this work we present the selection of six sustainable aviation fuels (SAFs) that will be included in TRANSCEND road-mapping. The full context of TRANSCEND and its findings for promising propulsion technologies are introduced in the complementary presentation: “Review of novel propulsion technologies for sustainable aviation from TRANSCEND” by Johan Kos. The reviewed SAFs included bio-based fuels and e-fuels as drop-in SAFs, and non-drop-in energy sources (here hydrogen). As part of the literature review, 19 groups of production technologies for SAF were initially identified, from which 5 technologies were discarded in the screening process due to either potential limitations on scalability or it very early technological development stage (i.e. very low Technology Readiness Levels). Subsequently, the 14 remaining technologies were comparatively analyzed for both their unitary production costs (i.e. costs per unit of usable energy [€/MJ]) and unitary greenhouse gas (GHG) emissions (i.e. CO2-eq. per unit of usable energy [CO2-eq./MJ]). As a result, five promising SAF production routes were pre-selected for further discussion with experts in a workshop; and at the end of the session six SAFs were selected for further evaluation in the roadmap, they are: hydroprocessed esters and fatty acids (HEFA), Fisher-Tropsch process (FT), fast pyrolysis (FP), Alcohol to Jet (ATJ), power-to-liquid (PtL) for e-fuel via Fisher-Tropsch, and alkaline electrolysis (AE) for hydrogen. Finally, the data collected on the life cycle GHG emissions, for most the relevant alternative energy sources and production routes, were used to develop an open Microsoft Excel based tool (the “Ecological Balance Sheet”) to quickly estimate a range of expected GHG emissions and the potential emissions savings of a production chain (based on similar systems already reported in literature).