Perspectives on Fully Synthesized Sustainable Aviation Fuels: Direction and Opportunities

Abstract

The aviation sector seeks to reduce greenhouse gas (GHG) emissions, with manufacturers and airlines announcing “zero-emission” goals and plans. Reduced carbon aviation fuels are central to meeting these goals. However, current and near-term aircraft, which will remain flying for decades, are designed around the combustion of petroleum-based aviation kerosene (e.g., Jet A/A-1). Therefore, the industry has focused on the qualification and approval of synthesized (e.g., non-petroleum-based) aviation fuel components with maximum blend limit percentages to avoid the blended fuel having properties outside the accepted ranges for Jet A/A-1. The synthesized components approved for blending are not necessarily interchangeable with Jet A/A-1. They may lack certain required chemical components, such as aromatics, or may have other characteristics outside the allowable ranges. To ensure safety, these synthesized aviation fuel components are only qualified to be used in commercial aviation when blended up to approved limits. The sector seeks to move toward the capability of using 100% synthesized aviation fuels that also meet sustainability criteria, known as sustainable aviation fuels, or SAF. However, these fuels must be developed, assessed, and deployed appropriately. This paper explores key questions relating to the introduction of 100% SAF, concluding that:• Near-term unblended synthesized aviation fuels must be “drop-in,” meaning they are compatible with existing aircraft and infrastructure.• Stand-alone complete fuels could be qualified within 1–2 years, with blends of blending components to reach 100% synthesized fuels to follow.• Sustainability criteria, while critical to sector acceptance, will continue to be assessed separately from technical performance.

Screening and evaluation of biomass upgrading strategies for sustainable transportation fuel production with biomass-derived volatile fatty acids

“…Property limits for diesel, jet, and gasoline fuels as well as corresponding properties of pure petrofuels are listed in Table 1 . We acknowledge that the fuel properties evaluated by VULTURE do not encompass every ASTM specification for each fuel application, such as required jet engine seal swell characteristics, 39 but they provide a reasonable set of first approximations which identify promising fuel mixtures. Mixtures which do not meet the specifications used in this work are likely not suitable for further study or advanced ASTM testing and thus do not merit further consideration.…”

Climate Impact Reduction Potentials of Synthetic Kerosene and Green Hydrogen Powered Mid-Range Aircraft Concepts

“…Furthermore, the Jet A-1 (ECLIF Ref 3) and the drop-in blend (ECLIF SAF2) were both used during flight campaigns measuring fuel impact on emissions and contrail formation [1]. The drop-in fuel is a 30% blend of HEFA (Hydroprocessed Esters and Fatty Acids) and Jet A-1 applies to ASTM D7566 fuel specification, whereas the power to liquid (PtL) synthetic fuel contains no aromatics and is thus outside current fuel specifications (starting in March 2021, different options for 100% Sustainable Aviation Fuel (SAF) specification are being discussed [2]).…”

Measurements of Nitrile Rubber Absorption of Hydrocarbons: Trends for Sustainable Aviation Fuel Compatibility

“…Namely, SAF is presently the only feasible option for long-haul flights, which are the largest contributor to aircraft emissions, and offers a high potential for backward compatibility with existing fuel and engine systems. However, until advancements in SAF technologies can guarantee 100%v “drop-in” capability, the specification for fuels containing synthesized hydrocarbons , limits SAF to a maximum of 50%v blending with conventional fuel. Resolving the motivating factors behind this blending limit are of high value to the industry as it works toward the stated production targets.…”