Phillips 66 and Afton Chemical are working together to develop and distribute an unleaded 100-octane avgas (UL100) that would eliminate dependency on the leaded 100LL currently used by most piston-engine aircraft. Afton Chemical is a subsidiary of Newmarket Corporation, which also owns Ethyl Corporation, a supplier of additives used to manufacture 100LL.

The new Phillips 66/Afton UL100 would contain no tetraethyl lead and it would be fully compatible with the existing 100LL fuel storage and distribution network and produce fewer harmful emissions than 100LL. It is too early for the companies to release cost information. “We understand cost sensitivities and are working on that,” said Afton senior R&D engineer Zach McAfee.

Phillips 66 would refine and distribute UL100, and Afton’s contribution is the additive package that helps bring the fuel’s octane rating to 100, to meet anti-detonation needs of high-compression piston aero engines.

Afton engineers have been working on UL100 for five years, according to McAfee. The additive package includes a manganese-based octane booster, as well as other components currently in 100LL—for example, one that helps with engine starting in cold weather. Afton has also developed a proprietary scavenger for the manganese, similar to the way ethylene dibromide is used as a scavenger for lead in 100LL.

Manganese in the small amounts needed for UL100 “would not meaningfully increase the amounts of manganese naturally present in air,” the companies explained. “Further testing and assessment will be undertaken to confirm that any emissions from the UL100 result in the expected improved environmental performance, and all such data will be shared with the U.S. EPA and FAA for review.”

Initial testing was done in a laboratory to ensure that the new fuel meets applicable specifications. Engine-run tests have been done on a dynamometer, including detonation testing on fuel-injected Lycoming 360 and 540 models. So far, detonation testing meets 100LL performance, he said.

Afton is preparing to conduct engine endurance tests in extreme conditions of high oil temperatures for long periods of running at high power and then to measure wear on individual engine components. Research and development is expected to continue through 2021. “We’re in the middle of the engine test program,” he said. Continental and Rotax engine tests are also planned, as well as flight testing.

Because the bulk components of the fuel are the same as 100LL, there is no difference in fuel density, and it should be able to mix with 100LL with no problems. There is no evidence of corrosion or seal damage by UL100.

Phillips 66 and Afton are working with regulators on certifying UL100, but the path toward certification is not entirely clear. “We are working with the FAA and other groups to help define and answer that question,” McAfee said. The companies are working with the FAA’s Piston Aviation Fuel Initiative Technical Evaluation Committee and as a member of ASTM International as well as the Unleaded Avgas Deployment Group to ensure that issues associated with moving the fuel from the refinery to the aircraft are all addressed.

Once all testing is done, Phillips 66 and Afton expect to seek fleetwide approval for UL100. “We’re working with the FAA to determine how that happens,” McAfee said.