Finding a drop-in unleaded replacement fuel option for aviation gasoline is proving more difficult than originally hoped, as the candidate selected by the FAA needs more work. In a recent update on research into the unleaded replacement, the agency said test results of an optimized fuel candidate from Shell “were not successful” and indicate a need for additional refinements.
Testing was conducted through the government/industry collaborative Piston Aviation Fuels Initiative (PAFI) during the first six months of the year. The agency also has been screening three addition fuels that were not previously part of PAFI.
“The scope of PAFI has continued to evolve with the preliminary evaluation of three other fuels representing PAFI's commitment to research and evaluate all candidate unleaded fuels,” the agency said. Shell further has committed to additional research and development to make necessary refinements, the FAA added.
But the results mark another setback for the program. In June 2018, the FAA said it had suspended flight-testing and certain engine trials of the two drop-in unleaded fuel candidates under evaluation and extended the target completion date of the program by one year to the end of 2019.
At the time, the agency cited differences between the two PAFI fuels—one from Shell and another from Swift—as compared with 100LL. In September 2018, the agency pushed back the target again to mid-2020, revealing that Swift had withdrawn from its participation from the PAFI program to pursue a fuel outside of the program. Shell, however, continued to work to optimize the fuel, and program participants agreed to resume testing last fall.
“PAFI's test experience, which brackets engine, aircraft, materials, and toxicology, has served to accentuate the extent of the challenge to identify an acceptable unleaded fuel for general aviation,” the agency said in the most recent update. “Accordingly, it is recognized that the scope of PAFI must expand to support the necessary research and development while engaging other candidate fuels for evaluation.”
The FAA said the program must be multifaceted and support continued government/industry collaboration.
