Multiple initiatives to spur production of sustainable aviation fuel (SAF) will soon lead to greater availability to business aviation operators. Even as today’s SAF blends come into their own, engine manufacturers and airframe OEMs are already looking to the next generation of “neat” SAF, free of all fossil fuels, for aviation use.
Currently, SAF is typically comprised of 30-50% fuel derived from renewable feedstocks, with regular, petroleum-based jet fuel filling the balance. However, testing indicates SAF completely derived from those same feedstocks can be used in jet engines without blending with any petroleum-based jet fuel.
“By the end of this year, all our production engines will have proved compatibility with 100% SAF.”
Stefan Wriege Head of External Communications, Civil Aerospace, Germany, Rolls-Royce
Gurhan Andac, engineering technical leader for aviation fuels and additives at GE Aerospace, noted no performance limitations or additional maintenance requirements with neat SAF. “Once we qualify unblended SAF as a drop-in fuel it will be reidentified as ASTM D1655 Jet A/A-1 fuel just as the blends of today; then we’ll be able utilize SAF’s full sustainability potential,” he said.
“SAF is essential for the decarbonization of long-range travel,” added Stefan Wriege, head of external communications for the business aviation unit at Rolls-Royce. “By the end of this year, all our production engines will have proved compatibility with 100% SAF. A few last tests are still outstanding, but we don’t anticipate any surprises.”
On the airframe side, Gulfstream Aerospace was an early adopter of blended SAF in its corporate and flight test operations and has flown its G650 on neat synthetic fuel. “We want to set the stage that today’s aircraft are ready for pure, drop-in SAF,” said company staff scientist/technical fellow Charles Etter.
The industry is also looking even further ahead toward paraffinic-only fuels produced from hydroprocessed esters and fatty acids (HEFA-SPK) in unblended form. These fuels are free of aromatics, which help aged nitrile-based engine and fuel system seals expand adequately to prevent leaks, but are also a significant source of particulate pollution.
While most modern aircraft engines now use non-nitrile seals, other components in aircraft fuel systems may require modification to safely use HEFA-SPK fuels. Etter noted positive results in tests conducted by Gulfstream on an unmodified G650 flown on a 90% HEFA-SPK blend with 10% aromatics added, with no leaks, so the potential is there.
“From an engine maker’s perspective, we would love to have non-aromatic fuels available that burn much cleaner and with much less emissions,” added Frank Moesta, senior vice president of strategy and future programs for Rolls-Royce. “We are working diligently to identify what measures are necessary to certify [HEFA-SPK fuels] so we can realize these great environmental benefits.”
“Sustainability is a key focus for industry and our company,” added Scott Evans, Gulfstream’s director for demonstration & corporate flight operations. “Our role in that effort is to provide resources [to SAF producers] to help open that envelope even larger.”
GE’s Andac emphasized the importance of business aviation remaining at the forefront of such efforts. “Utilizing SAF is very doable and is becoming more economically feasible,” he concluded. “I certainly encourage the business aviation segment to continue its adoption of SAF and give the signal to the industry.”