Navigating the power of sustainable aviation fuel (SAF)

Jeff Skinner

As the director of engineering for our Aerospace Group, Jeff leads global engineering activities for our fuel and motion control systems. He oversees new product development and introduction, research and development, and sustainability and aftermarket programs.

Jeff joined Eaton in 2001 as a stress analyst in our Jackson, Mississippi facility. He holds bachelor’s and master’s degrees in mechanical engineering from Mississippi State University. He is Eaton-certified in design for Six Sigma and a licensed Professional Engineer.

Steve Sipprell

Steve Sipprell is the director of next-generation air dominance (NGAD) systems for our Aerospace Group. In this role, Steve oversees all aspects of technical governance as well as systems design through certification and compliance. He also serves as the single point of contact for customer and Eaton leadership reviews of the NGAD program. Before this position, he was a chief engineer for our fuel and motion control systems.

With more than 37 years of experience in the aerospace industry, Steve has held various engineering leadership positions with McDonnell Douglas, Boeing and Eaton.

CREW: Welcome to Eaton's 10 in 10 podcast, where we focus on industry trends shaping the future of power management. In this series, our expert answers 10 questions about one of today's most talked about industry topics in 10 minutes or less. From the energy transition to digital transformation and beyond, we explore trends and discuss strategies for delivering safer, more efficient, and reliable power.

STEVE SIPPRELL: Hello. I'm Steve Sipprell, Chief Engineer with Eaton's Aerospace Group, here with a brand new10 in 10 podcast. Today we're talking about sustainable aviation fuel, or SAF for short. So why is this an important topic for us? As you know, aircraft platforms depend on traditional petroleum based jet fuel, which, unfortunately, contributes to carbon emissions impacting our environment. However, SAF is one of the industry's most promising pathways to decarbonization.

If you've seen any of the recent aviation news headlines, it's already showing tremendous progress and potential. Given the significant sustainability goals and targets ahead, I sat down with my colleague, Jeff Skinner, director of engineering for Eaton's Aerospace Group, to discuss SAF and its impact on the aerospace industry. Like other podcasts, we've got 10 questions in 10 minutes. And so with that, let's get going. Jeff, some of our listeners may not be familiar with SAF. Can you explain how it's different than traditional jet fuel?

JEFF SKINNER: Steve, sustainable aviation fuel is a non-conventional liquid fuel that incorporates sustainable feedstock instead of conventional crude oil or fossil fuel. The sustainable materials may come from a variety of sources, such as waste fats, oils, and greases, municipal solid waste, agricultural residues, or municipal waste. In addition, energy crops such as corn, grain seeds, and algaes could also be used to generate sustainable aviation fuel.

What may be surprising is that the chemistry of SAF is very similar to some of the traditional fossil jet fuel that we're familiar with today. SAF is produced by converting these materials into an aviation fuel that's suitable for mixing, or as a direct replacement for existing fuels. It can be also be created through synthetic processes, such as power to liquid, that involve capturing carbon directly from the air. 

STEVE SIPPRELL: Sustainable is a word used frequently today. So what makes SAF sustainable, Jeff?

JEFF SKINNER: Steve, this might be a lot easier to explain if I had an infographic, but I'm going to try my best to try to do it in this audio format. While the combustion process releases carbon dioxide, as all hydrocarbons, including petroleum and fossil based fuels, do, the production of sustainable or renewable feedstocks removes carbon dioxide from the atmosphere. It's balanced and it's a sustainable solution.

And again, just to repeat, the key here is that during production, the carbon dioxide is released when sustainable aviation fuel is produced. It's estimated that by shifting to sustainable aviation fuels entirely, we'll be able to reduce emissions by 88%. This assumes that all of the energy sources in the production are renewables, such as solar or wind power.

STEVE SIPPRELL: So given the different sources for SAF, are there different types of SAF that are produced?

JEFF SKINNER: Absolutely. There's multiple pathways to the production of SAF. And this is an active area of research within the industry. All of the different pathways produce slightly different fuel compositions. So it's something to pay attention to. So far, ASTM International, which is the governing body for fuel composition standards, has certified seven technical pathways for sustainable aviation fuel production. Each pathway involves different feedstock materials and chemical processes.

Of course, 100% sustainable aviation fuel would be most ideal, but none are currently certified as drop in by ASTM, primarily as a result of the unknown impacts of the varying fuel compositions. Some pathways to production do not produce aromatic content needed for today's fuel and engine systems, and today, these approved pathways require mixing of up to 50% sustainable aviation fuel with kerosene jet fuel. The blends, which are called drop-in replacements contain aromatic hydrocarbons that offer properties that are important for aircraft fuel systems and combustion.

STEVE SIPPRELL: So Jeff, why isn't SAF more mainstream today? At least the 50/50 blends that you spoke of?

JEFF SKINNER: Despite all the progress, there are a few challenges related to SAF adoption. One has to do with the magnitude of the jet fuel market. The increased demand for global air travel and aviation industry growth throughout developing countries will drive demand for more jet fuel in the next few years. It's expected that by 2026, we'll return to pre-pandemic industry fuel consumption levels of $95 billion gallons.

Global demand is expected to increase to 230 billion gallons by 2050, according to the Department of Energy. Production of SAF just isn't there yet in terms of how much would be needed to support worldwide travel, with just 4.3 billion gallons forecast to be produced in 2026. Another challenge is the cost. Currently, it's more expensive than traditional jet fuel to source, produce, manufacture, and package.

Costs need to be reduced for SAF usage to go up. With incentives in place, such as the Inflation Reduction Act, cost parity with petroleum based fuels is possible in 2027, albeit that's the year the IRA expires. Fortunately, government agencies, airlines, OEMs and consumers are working together to hit the industry's targets. It's going to take a collaborative effort to balance the SAF end to end life cycle.

STEVE SIPPRELL: Are current fuel systems and components compatible with SAF?

JEFF SKINNER: For most aircraft in service, the systems, components, and materials were designed for conventional jet fuel. Now that we're moving to cleaner and more efficient fuels, we need to ensure our systems are compatible. At Eaton, we've worked with several of our customers to understand the impact of SAF on our fuel components. We know that our current portfolio is compatible with drop-in SAF. However, we're still assessing the effects of non drop in compositions.

The elimination of aromatic content and non drop in SAF may require adjustments of seal materials and possibly other components. Our engineers continue to work alongside our customers and industry partners to investigate the impact of 100% SAF on all of our systems, from fuel pumps, engaging, to fuel inerting and materials.

STEVE SIPPRELL: So how will SAF impact fuel to system development in the future?

JEFF SKINNER: Steve, our understanding of the short to long term effects continues to evolve as we gather new research. I'm confident that what works for sustainable aviation fuel in the future will continue to work in applications using existing conventional aviation fuels. So while there may be changes required to accommodate non-drop-in SAF, those changes will be done in a way that tolerates any mix up to 100% SAF.

ASTM International has set a target of 2025 to define acceptable parameters for non-drop-in SAF compositions based on industry needs and what's possible. For right now, we're responding to impacts that depend on the range of fluid properties we're seeing across multiple drop-in SAF specifications. 

STEVE SIPPRELL: So in recent months a couple of 100% SAF powered flights made headlines. What does the success of these flights say about SAF?

JEFF SKINNER: This is an incredibly exciting time in the industry. It's exciting to see the OEMs and the airlines reaching key sustainability targets. Our team was excited to have our components on board two of these flights, one with Gulfstream and the other one with Virgin Atlantic. Gulfstream completed the world's first transatlantic flight on 100% sustainable aviation fuel on the G600 aircraft.

We were proud to support this endeavor by ensuring our fuel gauging technology would function over the seven hour flight from Savannah, Georgia to Farnborough, United Kingdom. Also, our fuel system supported Virgin Atlantic's achievement of being the first commercial airline to use 100% sustainable aviation fuel on their Boeing 787 aircraft. They took the aircraft from London to New York. Both flights leveraged a blend of SAFs to produce a composition similar to the drop in types we discussed before, but produced entirely from sustainable sources.

STEVE SIPPRELL: So, Jeff, do you see SAF as the most feasible pathway to net zero carbon emissions? 

JEFF SKINNER: It's a great question, Steve. Well, while we've talked a lot about SAF over the last few minutes, there's no singular path to net zero carbon emissions today. There's several technologies under development that will help the industry move forward to net zero by 2050. These include disruptive electric propulsion technologies such as efficient engines, as we've seen with the CFM rise, efficient aerostructures like we've seen with the TTBW program, electrification and more electric aircraft technologies, sustainable aviation fuel, production, manufacturing efficiencies, and of course, hydrogen fuel cells and hydrogen combustion long term.

We've seen a lot of progress across the value chain, but the growth of air travel in the same time horizon makes the hill much harder to climb. Going forward, achieving decarbonization will require a clear focus on short and long term initiatives. I can say Eaton is hard at work in supporting our customers on a number of these fronts, from developing more electric aircraft technologies to additive manufacturing of components to, of course, our work with sustainable aviation fuel. If I had to use a crystal ball, the solution for a net zero 2050, it's going to be a combination of all of these initiatives and innovations to reach the industry's decarbonization goals.

STEVE SIPPRELL: So what should we expect in the years to come?

JEFF SKINNER: First off, the aviation industry deserves a lot of credit for its ability to assess the impact of changes like this. Everyone is being as proactive as possible to remove barriers and achieve big milestones laid out ahead. In the years to come, I would expect to see more progress regarding technical pathways to sustainable aviation fuel, increased production, and increased usage across airlines. You should see sustainable aviation fuel in the headlines quite a bit, which is very exciting.

STEVE SIPPRELL: And lastly, Jeff, why should everyone listening be excited about SAF?

JEFF SKINNER: Well, what could be more exciting than cleaner and clearer skies? We've talked about the industry challenge as the volume of air travel increases over the next 20 to 30 years, and the promise of a net zero future is very exciting. It also brings about an opportunity for industry-wide collaboration, working together to make our environment and the world a safer, healthier place for all to live. 

STEVE SIPPRELL: Thank you, Jeff. It's been great speaking with you today, and we look forward to hearing more from you on this topic. To learn more about SAF and how we're supporting our more sustainable aviation industry, please visit eaton.com/aerospace.