100LL Drop-In Replacement ‘Impossible’ Says PAFI Candidate

The company behind the only candidate left in the FAA-driven Piston Aviation Fuel Initiative process to create a high-octane unleaded replacement for 100LL says it's impossible, according to Aviation Week. “There is no such thing as a drop-in unleaded fuel to replace 100 [LL],” Dan Pourreau, business development manager with LyondellBasel Industries, told the publication “We thought initially we were going to be able to do that, but we discovered we can’t do that either.” Pourreau said paper and technical modifications will be required on some engines to allow them to run safely on unleaded fuel. The LyondellBasell fuel UL100E is being evaluated through the congressionally mandated PAFI process at the FAA's test facility in New Jersey.

Pourreau did not discuss General Aviation Modifications Inc.'s (GAMI's) G100UL, which has an FAA supplemental type certificate to run in every spark ignition gasoline-powered engine used in aircraft on the FAA registry. Airframe STCs for helicopters are in process and were expected in the past few months but have not been released by the FAA. GAMI says the fuel works well in all engines and its lead-free formulation will extend engine life and maintenance intervals. To demonstrate its wide range of applications, the fuel was used to power the 2,000-horsepower radial engines in an A-26 that was flown to AirVenture.

Pourreau told Aviation Week the issue is achieving the 104 Motor Octane Number (MON) of 100LL. His team hasn't been able to do that without adding octane boosters that leave unacceptable deposits in the engines. “If you take lead out or you don’t use manganese or other octane boosters, the best you can probably do is roughly 100 MON or above," he told Aviation Week. "It is just virtually impossible to do that without changing other properties [of the fuel] so much, it’s no longer practical and effective.”