Sustainable aviation fuels are one of the key parts of the decarbonisation challenge for aviation, with the Destination 2050 initiative relying on them for more than a third of total reductions over the next 30 years. Amid daily announcements of agreements, partnerships and initiatives for SAF supply, and production at just 2% of current total fuel demand, how has more than a decade of on-wing operations unfolded, and what’s next for this critical technology?
[Subhead links: Sustainable aviation fuels | Destination 2050]
Over a decade since the first SAF test flights in the late 2000s, says Robert Boyd, assistant director for aviation environment at airline trade association IATA, “we’re at about 360,000 commercial flights so far. There’s fuel being produced every day, going directly into some airports. It’s business as usual, in select parts of the world and for a small group of airlines. It’s quite important that we’ve seen that step taken where some airlines have been able to go to a business-as-usual scenario where they may have a very small offtake of SAF — but it is an offtake, nonetheless, and there are daily flights happening.”
Boyd estimates that total 2021 production will be some 100 million litres — a far cry from the 5 million produced in 2016, but still requiring a massive scale-up, even with current limits per aircraft of 50% SAF to 50% fossil fuel kerosene. “The challenge really is: can we replace, say, three to four hundred billion litres?”
The numbers work out to a current production of between 3 percent of the total demand for jet fuel in 2019 (330 billion litres) and about 2.5 percent of the projected demand in 2050 (400 billion litres).
To get there, Boyd predicts, “through the 2020s, where there will be more tangible achievements, you’re going to see more physical SAF refineries come online, they’ll be producing fuel that’s going to be spread far more diversely across the world, we’re going to see different technologies showcased.”
This moves beyond HEFA fuels to Fischer-Tropsch and power-to-liquids and the rest of the currently certified SAF pathways — and of course to future options, where reductions of emissions could be up to 80% compared with conventional fuels, although the precise numbers are still up for discussion.
But how has aviation got to where we are?
From first testing to 50% drop-in
“Initial test flights by commercial airlines with blends of SAF started in 2008. Such flights are only authorised after a rigorous review and testing process, which includes aircraft rig testing in controlled laboratory conditions,” explains Nancy Young, vice president for environmental affairs at the Airlines for America trade association.
That review and testing process is largely governed by standards from ASTM, formerly the American Society for Testing and Materials, including the ASTM D4054 and ASTM D7566 standards.
Following the test flights, and further demonstration flights to show the potential for SAF supply, Young says, “A4A member carriers have been using SAF regularly on commercial flights from Los Angeles International Airport since 2016 and from San Francisco International Airport since 2020, and virtually all of our members have offtake agreements in place with existing or prospective SAF producers.”
So far, the usage of SAFs is largely via a “drop-in” model, somewhat akin to the E10 standard for automotive petrol where up to 10% of the total can be made up of renewable ethanol. In aviation, this percentage can currently be up to 50%.
This restriction, says A4A’s Young, “is typically because the petroleum-based jet fuel can convey other ancillary properties not naturally present in ‘neat’ SAF that the jet fuel storage and operating systems have been designed to rely on. A key area of research now, including testing and test flights conducted by Boeing and others, is to assess the array of equipment and parts associated with jet fuel systems to work toward using 100 percent “neat” SAF within the next decade.”
Young also highlights key areas of SAF research around new feedstocks, new production processes, improved, feedstock productivity, and carbon-capture as a feedstock.
Beyond 50% — and with certification
If IATA’s data show current SAF production at just 3% of current requirements, one might think that research and development to increase the percentage of SAFs allowed as drop-in fuels might not be a priority.
Not so, says Rohini Sengupta, senior manager of environmental affairs and sustainability at United Airlines: “it is critical to advance ongoing work to remove SAF blend limits, as it is a logistical issue to introduce blending and retesting to the process of bringing SAF to market.”
Particularly as new production sites come online, and as centres of early expertise like LAX and SFO grow, it may be that certain airports start edging closer to that 50% limit. Burning petroleum on the ground or sea to deliver lower-carbon fuel to other locations, of course, is hardly green.
Indeed, assuring that SAF supply can be examined, audited and certified with trustworthy carbon credentials is vital.
Crucial, says IATA’s Robert Boyd, will be “the ability to digitally track all of this information that needs to be collected and recorded by the airlines, particularly if they’re complying with different regulatory schemes around the world.”
One option, he notes, is “a book-and-claim-type accounting system for SAF. That then would mean that an airline could procure SAF from a location different to where it’s uplifting the fuel.”
Fundamentally, though, aviation needs to rapidly iterate its approach to SAFs. “The forward trajectory from test flights to regular revenue flights on SAF has taught us to be agile within a nascent market,” says United’s Sengupta. “While we’ve had several takeaways throughout the process, one of the main takeaways is that not all technologies work at every scale, and it’s critical to take every milestone we make as an opportunity learn if we want to grow our SAF usage and supply.”
Investment remains necessary from a variety of sources: airlines, producers, investors, governments and more — not only on a pure monetary basis to subsidise what is at present a substantially more expensive fuel, but to send demand signals that the industry is taking this seriously.
“It will be important to send these demand signals until such time that SAF supply tipping points are reached,” Sengupta concludes. “The Biden Administration recently announced a SAF supply goal of 3 billion gallons by 2030. I think the next decade is the time for all players — producers, airlines, investors, and the government — to look into growing SAF and rapidly scaling the market.”
Author: John Walton
Published: 21st October 2021
Lead Photo: Copyright San Franciso International Airport
