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Transformation of the energy carrier

Sustainable Aviation Fuels and Alternative Propulsion Systems

The most commonly used aviation fuel is kerosene, so-called Jet A-1, which is produced from petroleum. Its combustion produces CO2, water vapor, nitrogen oxides, soot particles and aerosols. Since kerosene is still indispensable on most routes today, research is being conducted into ways of producing kerosene from non-fossil sources. There are various production processes for these "Sustainable Aviation Fuels" (SAF), including Power-to-Liquid, HEFA and Alcohol-to-Jet.

In the Power-to-Liquid (PtL) process, renewable energy from wind or sun is converted together with hydrogen and CO2 into a synthesis gas. The Fischer-Tropsch process is then used to produce kerosene. Since the combustion of such fuels releases only as much CO2 as was captured during production, it is referred to as CO2-neutral fuel.

However, kerosene can also be produced from biomass. For the HEFA route (Hydroprocessed Esters and Fatty Acids), fats and oils from energy crops such as rapeseed, jatropha or algae, as well as from used fats (e.g. used cooking oil), are converted into fuel by means of hydrogenation and refining. In the Alcohol-to-Jet (AtJ) process, on the other hand, kerosene is produced from biogenic waste and residual materials. These are first fermented into alcohol and then further processed into kerosene by thermochemical reactions.

But even with synthetic kerosene, of course, it is not possible to fly CO2-free. Research is therefore focusing on electric propulsion systems that are powered either directly by electricity from renewable sources or by fuel cells using hydrogen. Smaller aircraft can already be operated purely electrically. However, kerosene will probably still be needed for long-haul flights.

Research focus

CENA aims to achieve carbon-neutrality through directly effective measures in aviation. The development of a strategy to substitute fossil kerosene with alternative aviation fuels (SAF) is therefore a focus of our work. We support the development of technology for the production of synthetic kerosene, in particular PtL, up to industrial production readiness.

A first step in this process is the construction of a PtL demonstration plant in Frankfurt-Höchst. To this end, the current technological readiness levels (TRLs) of various technology paths have already been analyzed and summarized in a study. It is also planned to promote currently less developed but promising processes and to avoid "duplicate research" of different plants and projects.

Regulation of SAF production and use

A possible regulatory framework is being developed as a model to allow the economically viable production and use of PtL fuel. At the same time, the preservation of the performance and competitiveness of German aviation in international competition is to be taken into account.

CENA is therefore following activities at both the federal and EU levels and assessing them in terms of their impact on the sustainability and economic viability of aviation. We are also actively involved in the work of associations and support the Hessian Ministry of Economics, Energy, Transport, Housing and Rural Areas (HMWVW) in its task of coordinating state activities on the federal PtL roadmap.

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