Approval by the aerospace industry for a standard for 100 percent drop-in sustainable aviation fuel (SAF) under development by an ASTM International task force likely won’t happen for another two years, according to the chairman of the standards organization's SAF panel and GE Aviation's aviation fuels and additives engineering leader, Gurhan Andac.
Andac told AIN the technical work the task force began in the spring of 2021 to restructure the existing ASTM D7566 standard “is essentially complete.” The existing ASTM D7566 standard specifies the properties of synthetic-fuel blends allowable for use in creating 50 percent SAF, but there remains no standard for synthetic fuel as such, he said.
The technical specifications the restructured standard will contain will probably include details of those synthetic fuel blends, produced from biological feedstocks by some of the seven existing chemical-conversion pathways for use in creating 100 percent drop-in SAF.
According to Andac, the SAF specified in the restructured D7566 standard will be capable of replacing conventional jet fuel in any turbine aircraft and in all existing jet-fuel infrastructure without any modification or equipment re-certification needed because chemically—and in terms of its energy density and other physical properties—it will mirror conventional Jet-A and Jet-A1.
The restructuring of D7566 by the ASTM task force provides technical specifications for the fuel properties—such as “maximums and minimums” for energy density, lubricity, ignition, and freezing points, etc.—required for 100 percent drop-in SAF, according to Andac.
But that doesn’t mean the standard can go into effect immediately once the task force sets the fuel’s technical specifications. The group now has started the important process of obtaining and responding to feedback from OEMs regarding the technical requirements they will have to meet, he said.
At the same time, the task force also must solicit from manufacturers the data requirements they need to meet to substantiate the processes for producing, handling, and using the fuel, according to Andac. Soliciting and understanding those data requirements will also involve a feedback-and-response process that will take place in parallel with the technical-requirements feedback loop.
Andac estimates it might take a year for the task force to work through the OEM feedback-and-response loops to the point where it is satisfied all stakeholders can meet technical and data-substantiation requirements to achieve the final 100 percent SAF specification.
After that, the task force will poll the full 500-organization membership of ASTM International to determine whether or not the membership accepts the specification. “The concurrence within the task force is that we’re likely to be in a position in about a year to go to ballot,” said Andac. If any members vote not to accept the specification proposed by the task force, a process of adjudication would begin to address any conflicts.
The balloting and the potential subsequent adjudication process could also take about a year in total to complete, he said. Even after the completion of that process, however, “there is still some work to do” before the 100 percent drop-in SAF standard can go into effect, said Andac.
One important piece of work the task force must pursue centers on “targeting a way to get to the 100 percent drop-in standard by blending synthetic components,” said Andac. (The 100 percent drop-in SAF that CFM International and GE Aviation used to fuel one of the Leap-1B engines of a United Airlines Boeing 737 Max 8 for a demonstration flight in December from Chicago O’Hare to Washington Reagan airport contained a blend of several synthetic components.)
Even with the 100 percent drop-in SAF specification finally in place and production of synthetic fuels via various conversion pathways accelerating, the fuel would not be usable in any manufacturer’s equipment until each OEM updates the technical documentation to reflect their suitability for drop-in SAF. So, OEMs will have important documentation-revision work to perform once all stakeholders agree to the 100 percent drop-in SAF standard, according to Andac.
Developing a Standard for 100 percent Non-Drop-In SAF
By that time a new initiative—launched just before mid-April 2022—by the ASTM SAF task force to develop another restructuring of the D7566 standard to provide specifications for a 100 percent non-drop-in SAF will have gotten underway. Approval of that standard will likely take place a year or more after the 100 percent drop-in fuel has received final approval by the ASTM membership, according to Andac.
Like 100 percent drop-in SAF, the non-drop-in fuel that eventually will receive industry approval probably will consist of a blend of paraffinic and aromatic synthetic biofuels. Unlike in the case of 100 percent drop-in SAF, however, each item of equipment must gain certification for safely handling 100 percent non-drop-in SAF because the non-drop-in fuel will not chemically and functionally duplicate jet-A.
Despite that requirement, “there is some drive to consider this type of SAF as a potential fuel because it has some additional benefits,” said Andac. They include reductions in particle emissions, fuel-burn improvements resulting from its higher heat content than drop-in SAF, and its greater availability than the drop-in alternative, he said.
But development of the 100 percent drop-in SAF and 100 percent non-drop-in SAF standards would result in little practical benefit to the aerospace industry if the production of synthetic fuel components from biological and other feedstocks can’t meet the massive demand to replace fossil-derived jet fuel.
So policy and regulatory developments incentivizing and facilitating large-scale production of SAF are just as important for aviation worldwide as the development of technical standards for drop-in and non-drop-in fuels, according to Chris Lorence, GE Aviation’s chief engineer.
“From a policy standpoint, it is important that we get the industry moving in a harmonized way,” said Lorence. “Right now, there are a number of different incentives and mandates in the UK, Europe, and the U.S. We would like to see a harmonization effort to get the kind of production we’re looking for.” That level would allow the aviation industry to meet its goals of producing 3 billion gallons of SAF annually by 2030 and 35 billion gallons annually by 2050, replacing all fossil fuel-derived jet fuel.
It is equally important for fuel producers not to wait until the ASTM members approve the two 100 percent SAF standards before ensuring adequate production levels to meet what will become soaring demand for SAF, according to Andac.
“There is no need to have SAF standards in place to develop feedstocks and production capacity,” he said. But an immediate need does exist for SAF production to begin accelerating for the creation of an international SAF regulatory framework and a synthetic fuels ecosystem. “These are more important right now than the 100 percent standard is,” concluded Lorence.