How SAF Experimentation Is Fuelling Change for Military Operators

by Mark Pilling (Flight Global) Over the past six months, an Airbus Defence & Space A400M tactical transport, NH Industries NH90 multirole helicopter and a Eurofighter Typhoon have become the latest military aircraft to undertake test flights with sustainable aviation fuel (SAF).

They join a growing list of defence assets demonstrating the suitability of SAF as a drop-in fuel, replacing kerosene, that have taken to the air over the past decade and more. SAF is seen as the most critical ingredient in aviation’s mission to reduce its carbon emissions up to 2050 and beyond.

Air BP offers this explanation of why SAF is important: “SAF gives an impressive reduction of up to 80% in carbon emissions over the lifecycle of the fuel compared to the traditional jet fuel it replaces, depending on the sustainable feedstock used, production method and the supply chain to the airport.”

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Typical feedstocks used to make SAF are cooking oil, animal waste fat, solid waste from homes and businesses and forestry waste, it notes.

Air BP is one of a multitude of SAF producers from the ranks of the traditional fossil fuel giants along with a host of start-ups keen to tap into what could become a huge market. Air BP was also the supplier of the SAF used in mid-January by a Royal Air Force (RAF) A330 Voyager tanker to achieve the first SAF air-to-air refuelling of a Typhoon and Lockheed Martin C-130J transport.

The alternative pathways are easy to describe. The first is alternative fuels, such as SAF, which require no engine modifications. The second is to change the way the war-fighting machines are powered by developing engines that use a low-carbon fuel source such as electricity or hydrogen.

Another attempt with alternative fuels took place in the late 1950s, when Lockheed’s famous Skunk Works unit used liquid hydrogen as a fuel in ‘Project Suntan’ to develop a long-range spy plane.

According to Michael Winter, principal fellow advanced technology at Pratt & Whitney, which was the engine developer for the CL-400 Suntan, while the project was cancelled, it enabled P&W to understand the challenges of making a gas turbine engine powered by hydrogen.

P&W is one of several engine innovators revisiting hydrogen today. “We went back to the technology from Project Suntan and we’re now working on a hydrogen engine variation on that cycle,” says Winter.

“This is an issue right now. When we go into foreign military campaigns for F135 engines, among the 15 allied operators that we have for the [Lockheed] F-35 we now have countries asking us and the OEM to perform life-cycle analyses on the engine and on the aeroplane,” Winter says.

For instance, in Switzerland’s recent fighter competition, which featured a public referendum on the aircraft choice, “there were hearings that included discussions about the sustainability and fuel burn associated with the various options for the Swiss air force,” explains Winter. These considerations are mostly prevalent in Europe and emerging in the USA, but will grow, he adds.

In late 2022, the US Department of Defense (DoD) was tasked to prepare a plan for increasing the production and use of SAF in the Pentagon’s aviation operations. Under the 2023 National Defense Authorization Act (NDAA), the DoD will have one year to identify at least two “geographically diverse” sites within the current US military footprint to carry out a pilot programme on SAF use.

Following an initial year to identify test sites, the DoD is required to generate a plan for using a jet fuel blend of at least 10% SAF by 2028 at these bases.

The US military has been involved in the development of SAF for over a decade. In 2010 an unmodified US Navy Boeing F/A-18F Super Hornet flew from NAS Patuxent River in Maryland powered by a 50:50 blend of sustainable biofuel and jet fuel.

At the time, Boeing said that “operating navy platforms with renewable energy sources such as sustainable biofuels are part of the service’s strategy to reduce reliance on fossil fuels by half over the next decade”.

While FlightGlobal’s research has not found any military forces regularly using SAF, there are many military models on the path of testing and certification, including with the Japan Air Self-Defence Force and the Republic of Singapore Air Force, and there are infrastructure developments. From January, the NATO Central Europe Pipeline that supplies Brussels airport with kerosene was opened for the transport of SAF.

In parallel there is a frenzy of R&D work around disruptive propulsion technologies with direct applicability between the work being done in the civil world to military platforms, says Winter. All of P&W’s military engines are approved for SAF use based on today’s fuel specifications and the F135 engine for the F-35 has run on 100% SAF.

The prospect of producing sustainable aviation fuel utilising embryonic carbon transformation technologies has led the US Department of Defense to begin work with a start-up in this field to explore the opportunity.

The deal in February saw developer Air Company awarded a contract with a ceiling value of $65 million from the Defense Innovation Unit to produce Airmade jet fuel at certain selected US Air Force (USAF) bases.

Air Company notes that the USAF is currently identifying and developing potential sites suitable for its Airmade SAF production across the USA, to be available ahead of 2030.

In mid-2022, the USAF and Air Company kicked off their partnership with a flight demonstration of a small, unmanned jet powered 100% by Airmade SAF in a project called Fierce.

Air Company produced five gallons of SAF using its carbon utilisation technology. This features its carbon conversion reactor system, where carbon dioxide captured from industrial plants is combined with green hydrogen. There are further steps involving a catalytic converter to finish with a SAF that Air Company claims has an emissions reduction potential as high as 99%, depending on the low-carbon electricity source used. READ MORE