As the supply of sustainable aviation fuel (SAF) slowly ramps up across aviation, the business aircraft sector engine manufacturers are wasting no time in qualifying their products to operate on the alternate fuel—both blended and, ultimately, at 100%.

General Electric (GE), which is producing the Passport engine for Bombardier’s Global 7500/8000 and CF34-3B for the Challenger 650, continues to test engines with 100% SAF, says Gurhan Andac, GE Aerospace engineering technical leader for aviation fuels and additives.

“In 2022, GE’s Passport engine and the HF120 engine, a product of GE Honda Aero Engines, were both ground-tested at our Peebles Test Operation with 100% or unblended SAF,” Andac says.

The test plan forms part of “ongoing efforts in the industry to assess and qualify 100% SAF, which has not yet been approved for commercial use by ASTM International, a standards-setting body,” Andac adds.

“Meanwhile, all GE Aerospace engines can operate with approved SAF blends today, which can be mixed with conventional jet fuel up to a 50% limit. According to the Air Transport Action Group, more than 488,000 flights have been fueled with SAF blends since 2011,” he says.

The aviation industry is currently targeting agreement on a 100% drop-in SAF standard by 2025.

Andac notes: “A standard has been drafted and is going through an OEM (original equipment manufacturer) feedback process, which takes time. Following the feedback loop, the final draft will go through ASTM balloting for wider stakeholder review. If successful, that will constitute as the approval of 100% SAF use as fully synthetic Jet A and Jet A-1.”

GE, which has been involved in assessing and qualifying various forms of SAF since 2007, has—like most OEMs—focused recent tests on the use of Hydroprocessed Esters and Fatty Acids Synthetic Paraffinic Kerosene (HEFA-SPK), which is the most widely available SAF today. HEFA-SPK can be made from cooking oil and other waste fats, oils and greases.

“We have put together a technology plan at GE Aerospace to assess our current capability and, if need be, develop capability to accommodate higher-blend-ratio SAF and non-traditional SAF options for the airlines and operators to be able to use in the future with our products,” Andac says.

Honeywell, which currently produces four versions of the HTF7000 engine family for Bombardier, Embraer, Gulfstream and Textron Aviation—as well as the final new-build versions of the stalwart TFE731 for Dassault—says all its propulsion engines and auxiliary power units (APUs) “are currently certified to operate on a 50% SAF blend.” John Head, Honeywell vice president for engines, says the company's “future roadmap and associated ground and flight-testing plans will enable our engines and APUs to operate higher SAF fuel blends, up to 100% SAF.”

As part of plans to support further testing of all commercial engines, APUs and R&D work, Honeywell has begun receiving monthly shipments of SAF starting in January 2023. The fuel, developed by World Energy in California and distributed by World Fuel Services, is delivered to the company’s main campus in Phoenix, Arizona, adjacent to Sky Harbor International Airport.

Covering the full range of business jet power—from the light, mid-size, super mid-size and large aircraft markets with the PW600, PW500, PW300 and PW800 families, respectively—Pratt & Whitney says “expanding the use of SAF is critical to realizing the industry’s goal of net-zero emissions, and enabling operation with blends of up to 100% SAF will maximize the potential environmental benefits.”

The company, which continues to base its profitable small engine business out of Canada, says it has developed “a clear and funded testing plan covering all engine families over the next 3-4 years to ensure 100% SAF compatibility. This includes our business aviation engines models such as the PW300/PW500/PW600 and PW800.”

In April 2023, Pratt & Whitney Canada meanwhile received its first delivery of 100% HEFA-SPK SAF at its Arizona and Montreal facilities to begin additional testing on PW800 and PW300 engines. The company also recently announced a new project, supported by the government of Quebec, which will enable further research and testing on a range of different SAF types, including synthetic e-fuels developed by the SAF+ Consortium.

“We’re also working with Airbus to conduct 100% SAF flight testing on the PW1500G geared turbofan-powered A220 aircraft, which of course also serves the business aviation market as the ACJ220. Certification of 100% SAF will ultimately depend on ASTM International defining a specification for that fuel, which could occur as soon as 2025,” the engine-maker says.

Rolls-Royce—which, despite recent inroads by GE and Pratt & Whitney, still dominates the large business jet market with the BR700 and Pearl engine families—is committed to demonstrating compatibility with 100% SAF, says Simon Burr, director of Rolls-Royce product development and technology for civil aerospace.

“We've done ground tests of the Pearl 700 and flight tests of the BR725. The testing today has shown us the things that we expected, and we've not just done tests to tick a box—we've taken measurements like ECLIF. It’s been significant research,” Burr says, referring to the Emission and Climate Impact of Alternative Fuels (ECLIF) program involving Airbus, Rolls-Royce, German research center DLR and SAF producer Neste.

In the first ECLIF1 campaign in 2015, DLR investigated alternative fuels with its Falcon 20 and A320 research aircraft. In 2018, the ECLIF2 campaign saw the A320 flying with a mixture of standard jet fuel and up to 50% HEFA. This paved the way for ECLIF3 in 2021, which marked the first time 100% SAF was used simultaneously on both engines of a commercial passenger aircraft—an Airbus A350 aircraft powered by Trent XWB engines.

Further testing planned for this year includes 100% SAF on a Pearl 10X, the engine selected for the Dassault 10X, as well as on a BR710 and Pearl 15. The Pearl 10X has additive layer combustor tiles, “so it's useful to do that test,” Burr says. The BR710 is slated for tests “because there's a very substantial fleet of aircraft and it's still in production,” he adds. The Pearl 15, meanwhile, is in production for the newly developed Bombardier Global 5500 and 6500.

“All this work at 100% SAF—at the heart of it—is understanding our systems and making sure our combustion systems and pumping systems and controls are working the way we expect,” Burr notes.

“But you don’t need to test all these engines to do that," he adds. "These are to address different customers and different segments of the market, but the strong part of it is advocacy. This really gives regulators and the government confidence to set a framework for sustained investment."

Burr continues: "So, whether the government's choosing to do it by regulation or by taxation incentivizing, that's what we're trying to do by giving them the confidence that there's not a technical block with the engines.”

Technically, Burr points out that SAF is also advantageous in operational terms. “You get cleaner combustion with low aromatics,” he says.

Williams International has also quietly continued SAF compatibility tests following its early demonstration flight in 2021 of an FJ44-4 fueled by 100% SAF. That flight, which lasted 3.5 hr. with a maximum cruising altitude of 45,000 ft., was conducted out of Williams’ flight operations center in Pontiac, Michigan, using the company’s experimental flying testbed.