Hydrogen End Use – Sustainable Aviation Fuel
Sustainable Aviation Fuel (SAF) is a term used to describe non-fossil-based fuels used in the aviation industry to reduce the sector’s carbon footprint. While hydrogen itself is not a SAF in the traditional sense of being a drop-in fuel that can be blended with or directly replace jet fuel without significant modifications to aircraft or infrastructure, it is considered a key component of the future of sustainable aviation through different pathways:
Direct Burn in Engines
Hydrogen can be used directly as a fuel in jet engines. However, this requires significant modifications to the aircraft’s fuel storage, distribution systems, and engines due to hydrogen’s low density (requiring more volume for the same energy content as conventional jet fuel) and cryogenic storage requirements (as liquid hydrogen is stored at -253°C). This pathway represents a more radical departure from current technologies and infrastructure.
Hydrogen Fuel Cells
Hydrogen can also be used to power fuel cells, converting the chemical energy of the fuel directly into electricity and water. This electricity can then power electric motors to drive the aircraft’s propellers or fans. This approach is particularly promising for smaller aircraft and shorter routes due to current limitations in energy density and storage compared to conventional jet fuels.
As Feedstock for SAF Production
Perhaps most relevant to the traditional concept of SAF, hydrogen can be combined with captured carbon dioxide (from the atmosphere or industrial sources) to produce synthetic fuels, including synthetic kerosene. These synthetic fuels can be designed to be drop-in replacements for conventional jet fuel, requiring no modifications to engines or aircraft. This process, often referred to as Power-to-Liquid (PtL) or the Fischer-Tropsch process (when involving a series of chemical reactions to convert a mixture of carbon monoxide and hydrogen into liquid hydrocarbons), enables the production of carbon-neutral fuels if renewable energy sources power the hydrogen production.
Hydrogen’s role in sustainable aviation, therefore, spans direct use to synthetic fuel production, offering pathways to significantly reduce the aviation industry’s carbon footprint. Each of these uses comes with its own set of challenges, including energy efficiency, infrastructure development, and economic viability, which are currently the focus of extensive research and development efforts across the globe.
Latest News
In a discussion highlighted by Hanneke Weitering on June 8, 2023, experts, including Rolls-Royce’s Frank Moesta, advocate for utilizing hydrogen primarily to produce sustainable aviation fuel (SAF), rather than for direct use in hydrogen-powered aircraft. The argument is based on the practicality and immediate applicability of eFuels—a type of SAF synthesized from green hydrogen and captured carbon dioxide. These eFuels can be used in existing jet engines without modifications, offering a more accessible and sustainable alternative to conventional jet fuel derived from agricultural feedstocks.
The production of eFuels is seen as particularly advantageous for business aviation, where smaller airports lack the infrastructure for direct hydrogen fueling. Challenges remain in reducing the cost of green hydrogen production to make eFuels economically viable. However, the broader potential of hydrogen as a versatile tool for decarbonization, beyond just aviation fuel to applications like agriculture, underscores a holistic view of its benefits. The consensus suggests a strategic focus on hydrogen for SAF production as the most effective path forward for the aviation industry’s sustainability efforts.