Readers have likely seen or heard a lot of things recently about the aviation industry pursuing 100% sustainable aviation fuel (SAF) as part of its decarbonization commitments. There have been multiple news stories about research activities and flight demonstrations that have used 100% synthetically derived SAF. Some of these may even have generated some angst for readers, especially those associated with airport fuel handling, who wonder if they are going to have to deal with fuel segregation requirements going forward. Understanding synthetic jet fuel activity requires some nuance and understanding of detail, and therefore the headlines coming from the industry have been viewed by some as confusing or inconsistent with expectations regarding the focus on drop-in fuels that can be used in existing infrastructure and aircraft. So it should be no surprise that many have reached out to Commercial Aviation Alternative Fuels Initiative asking, “What are these efforts, what do they mean? Are these still drop-in fuels, and is the industry changing strategies?”The short answer to the last question is, no, the aviation industry is not changing strategies. These activities simply provide a glimpse into the depths of the strategy the aviation industry has been pursuing since before the aviation sector’s first Industry Commitment to Action on Climate Change in 2008. The entire industry continues to pursue SAF, drop-in synthetic fuels that can deliver significant lifecycle greenhouse gas (GHG) emissions reductions (and other environmental and social benefits) at reasonable costs. This strategy includes moving beyond the blending requirements found in the current SAF specifications and addressing the opportunity for up to 100% synthetic jet fuels produced from an ever-broadening range of SAF production pathways (i.e., new hydrocarbon feedstock sources and conversion technologies).The industry has been using SAF continuously since its initial introduction in 2016 at Los Angeles International Airport. That first million gallons of SAF was produced via the hydroprocessed esters and fatty acids (HEFA) pathway, defined in ASTM Specification D7566 Annex A2. The SAF was delivered at blend levels between 30% and up to 50% with petroleum-based jet fuel and delivered 60% to 80% reductions in net GHG emissions per gallon consumed. Fast-forward to 2023, when the International Air Transport Association reported an estimated 158 million gallons of neat SAF production worldwide. In the U.S., EPA highlights the usage of 26.3 million gallons of RFS-compliant neat SAF blending component in the U.S. in 2023 and 9.6 million gallons in January 2024 alone! This is evidence of the industry entering a growth trajectory that's anticipated to deliver on various SAF commitments and policy, goals and mandates being created worldwide (e.g., the 3 billion gallon per year U.S. production goal of the SAF Grand Challenge by 2030).ASTM specifications currently require SAF to be blended with petroleum-based jet fuel at levels up to 50%. We recognize that removing blending restraints on current SAF production concepts is one of the ways to accelerate decarbonization for the sector while also potentially reducing costs and net lifecycle carbon. However, such an approach can only be done within the bounds of a fuel that meets the specifications needed to maintain the type certificate of existing aircraft—i.e., a drop-in fuel.How and when can the aviation industry use 100% synthetic aviation turbine fuel that also delivers the sustainability society expects from the sector?&nbsp; Aviation manufacturers will continue to ensure that their aircraft (legacy, in-production, pending and future concepts) are able to operate on all drop-in fuels. &nbsp;This is the essence of the industry’s fuel qualification approach outlined in the requirements of the ASTM D4054 specification. It is worth noting that the current fuel specification allows a great deal of flexibility in the composition of jet fuel. Each jet fuel refiner (petroleum-based or otherwise) around the world produces fuel that is molecularly distinct, predicated on the type of crude they use and the processes in the refinery. But they all produce a fuel that falls into the range of physical and fit-for-use properties defined and bounded by the jet fuel specification (ASTM D1655).While we support ongoing efforts to qualify SAF that is fully compatible with today’s fleet of aircraft, manufacturers are also working to ensure that new aircraft produced after 2030 will be able to use as wide a range of drop-in SAF types as possible, including up to 100%. The 100% SAF demonstration flights in recent months by United Airlines, Emirates, Gulfstream and others relied on obtaining aromatics that were produced from biomass. However, the current requirement that we have aromatic content in such SAF blends makes it more costly to produce and distribute SAF. This is due to an additional blending step that is often required to introduce these compounds into the fuel.In terms of expanding potential drop-in SAF compositions, one example is the consideration of jet fuel formulations with varying aromatic type and content. Aromatics are important components in today’s petroleum-based jet fuel, delivering physical and fit-for-purpose attributes for the aircraft. Unfortunately, certain aromatic compounds such as polycyclic naphthalenes can generate particulate matter during combustion. Research also indicates that their removal from jet fuel may help mitigate the formation of persistent contrails that represent a non-CO2 climate impact of aviation. Removing these specific aromatics, naphthalenes, from the fuel will likely reduce the negative impacts of aviation on air quality and radiative forcing. However, the removal of all aromatics will likely have negative impacts on operability and efficiency. Nevertheless, there may be ways to tailor certain 100% synthetic definitions, such that we get advantaged fuel formulations without naphthalenes. &nbsp;For example, testing has shown that certain cyclo-paraffins and non-naphthalenic aromatics can replace less desirable aromatics while still delivering a drop-in SAF. The aviation enterprise is collaborating with the research community and fuel producers on utilizing the full range of the fuel specification, comprised of various types and quantities of synthetic components that still result in a drop-in SAF, and getting such fuels qualified for use by 2030.What signs of progress should we expect to see next?&nbsp; An industry task force has been convened under subcommittee ASTM D02.J0 to facilitate the evaluation and approvals needed for 100% drop-in SAF. There are several potential ways to achieve the qualification of higher SAF blending component, or even 100% SAF, that center around the idea of producing a set of molecules that fully match the overall characteristics of jet fuels refined from petroleum. These concepts include:• Current approach: The current approach requires synthetic blendstocks to be blended with petroleum-based jet fuel. This is the approach we have been using since the start of our SAF journey and is reflected in the qualified pathways found in the Annexes of ASTM D7566 (eight at present and increasing) as well as the coprocessing pathways found in Annex A1 of D1655 (three at present and increasing). In some cases, we may be able to increase the maximum level of allowable blending.• Near-term advancements: These advancements allow specific pathways that produce fully formulated SAF (with all the required molecular components necessary for performance and safety), mimicking petroleum-based jet, to be qualified under the ASTM D7566 (e.g., potentially three of the existing pathways that include certain C7-C17 range iso-, normal-, and cyclo-paraffins and aromatics as well as other approaches going forward).• Closely following the near term: These advancements allow individual blending components of already qualified pathways to be blended to get to 100% drop-in SAF. &nbsp;This solution may not help as much with cost, except in some unique circumstances, but will help with maximizing net carbon reductions out of any gallon of SAF used.So, progress on these concepts will not be widely discussed in public, but will be worked toward behind the scenes within the fuel specification subcommittees (several hundred aviation fuel specialists from across the industry and around the world) and unveiled as changes to D7566, likely within the next 18 months.What else is being worked on?&nbsp; Some aircraft may also be able to operate on nondrop-in fuels, today or tomorrow, to achieve various operational efficiencies (for example, utilizing fuels with higher-energy-per-unit mass, higher-energy-per-unit volume, or having greater heat capacity). &nbsp;However, the aviation industry recognizes there are many nonaircraft issues to address before these concepts can advance to commercialization, if ever. The industry will continue to explore such in the background (e.g., through the collaboration of the International Aerospace Environmental Group) to see if these issues can be addressed in meaningful ways (e.g., through aircraft modifications) where the benefits clearly outweigh the risks and costs for all jet fuel consumers. One of the outcomes of this evaluation is the potential creation of a nondrop-in jet fuel specification being referred to by various names (e.g., Jet-X, 100% HEFA), primarily for use by the manufacturers in evaluating future designs under a common understanding of any potential new fuel definition. The use of hydrogen as a gas turbine fuel falls into this category of future evaluation efforts. So, when you hear about such concepts, do not confuse them with the mainstream activity around which the entire aviation enterprise is aligned—moving to affordable, sustainable, 100% drop-in SAF.Takeaway&nbsp; In conclusion, yes—there has been a great deal of interest in the aviation sector to accommodate 100% SAF to maximize GHG emissions reductions without negatively impacting aviation’s ability to deliver on its value proposition of safe, high-speed movement of people and freight.Aircraft and gas turbine jet engines are robust in their designs and operability, which contribute to aviation’s safety. Nondrop-in fuels can likely provide fundamental power production in an engine, but they are not considered viable in the near term, as they will require changes to delivery and storage infrastructure, engines, aircraft, etc., at greater-than-practical societal cost. While such concepts are still being researched (e.g., to prepare the industry to fend off uniformed policy pursuits), they are unlikely to reach commercial viability in the foreseeable future.Aviation advocates should join us in welcoming 100% SAF concepts in the near term and expect to hear more as such efforts continue. Rest assured that such adoption doesn’t need to cause apprehension. The systems are in place to ensure that 100% SAF can be produced and used safely as drop-in fuels with existing systems and airport infrastructure, and such an approach helps accelerate the industry toward achieving its commitments.Author: Steve Csonka&nbsp; Executive Director, Commercial Aviation Alternative Fuels Initiative&nbsp; www.caafi.org&nbsp;

2024-03-12 - What’s All This Noise About 100% SAF? (SAF Magazine)

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How and when can the aviation industry use 100% synthetic aviation turbine fuel that also delivers the sustainability society expects from the sector? 

What’s All This Noise About 100% SAF?

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