Clean avgas substitute aims for summer approval

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A test fuel specification for SwiftFuel, a biofuel designed to replace leaded avgas, could be resubmitted to ASTM International in February after three negative votes from ASTM members in December led Swift Enterprises to withdraw and rewrite its proposal.

Extensive testing of aircraft fuel systems, engines and materials compatibility could begin after ASTM's June meeting in Kansas City. Avgas is being forced into extinction because of harmful lead additives.

"A specification was needed to permit Swift to manufacture the fuel and test it, thereby creating the technical database needed for a research report to verify that the product has met the requirements that they specified," says Stan Seto, chairman of an ASTM aviation fuel subcommittee.

Testing thus far shows no deterioration of plastic or rubber engine components, and its high octane has made SwiftFuel the top candidate to replace leaded avgas. Swift Enterprises, based in Purdue Research Park in Indiana, is already exploring large-scale testing partnerships, says Mary Rusek, president and co-owner.

Industrial-scale production is needed to reach refinery prices of $2 per USgal (52¢ per litre) and $4 per USgal retail prices, using sugars, cellulose and lignin as feedstocks.

The USA is the biggest consumer of avgas, or 100LL, where high-performance piston aircraft and vintage warbirds comprise about 25% of the general aviation fleet and require the high octane rating.

FAA testing at the William J Hughes Technical Center measured the motor octane number of SwiftFuel at 104.1, higher than avgas and experimental non-leaded petroleum substitutes. Its report says: "On a volume basis, the Swift 702 fuel contained 13% more energy than the 100LL. Operation on the Swift 702 fuel resulted in an average decrease in volumetric fuel consumption of approximately 8%."