Avgas Alternative

Avgas Alternative

New 82UL specification is an attempt to make piston aircraft fuel environmentally friendly, more affordable

BY John Boyce, Contributing Editor

January / February 1999

After 10 years of repeated testing, arguing, and voting, the American Society for Testing and Materials (ASTM) has produced a specification for an unleaded aviation gasoline. On November 10 the dispute was settled by a ballot of an ASTM aviation fuel subcommittee (officially, Sub-Committee J), comprising members from all aspects of the aviation and fuel industries. The following day, ASTM D6227 standard specification for grade 82 unleaded aviation (82UL) gasoline was published and became an official aviation fuel.

"It's done, it's an official specification," explains Dr. Cyrus Henry, a research fellow at Octel America in Newark, DE, and ballot secretary for the ASTM subcommittee.

In an earlier interview, Henry said, "This has been a real contentious process. It's an effort to make an aviation gasoline more available for low performance, piston-powered aircraft. You need 100 (octane) for larger aircraft; this is for low compression engines....

"This was an effort to develop a fuel specification that would result in something that was more readily producible from motor gasoline stocks. In its origin, the idea was practically rebranding motor gasoline as aviation gasoline. But by the time this evolved fully, that's no longer the case. This is now pretty much a stand-alone aviation fuel."

Although in practical terms, 82UL will, indeed, come from basic unleaded automotive gasoline stock, there are requirements and specifications that distinguish it from unleaded auto gasoline. For instance, the addition of alcohol is prohibited as are deposit control additives (an EPA requirement in autogas); stability test requirements are more stringent; and, the vapor pressure limits are different.

OEMs lead the way
The Environmental Protection Agency has not put any deadline on eliminating lead from aviation fuel, but it is clear it was looking for aviation to make progress in that direction. In addition, the sources of tetra ethyl lead (TEL) are drying up worldwide and the rules for handling it in this country are increasingly stringent. Recognizing these facts and wanting to create more sources of aviation fuel for its piston aircraft now and in the future, Cessna became the prime and vigorous mover in the development of an unleaded aviation gasoline standard. (Cessna and other OEMs don't approve the use of motor gasoline in their aircraft engines.)

In fact, Cessna and Lycoming have developed an engine that is designed specifically to operate with 82UL. They have been unable to apply for certification because until now they didn't have a standard specification for the fuel to show to FAA.

A similar situation exists for those aircraft with Supplemental Type Certificates (STC) to operate on automotive gasoline. It's the position of the Experimental Aircraft Association that the aircraft already holding STCs for autogas can operate safely on 82UL. However, without a published, therefore official, fuel specification, they could not ask FAA to issue a clarifying notice to that effect.

"It is our understanding," says Earl Lawrence, director of government programs at EAA, "that those aircraft that currently hold STCs for autogas can operate on 82UL because the requirement for the STC said that the aircraft must use fuel that meets the autogas specification ... If you use the 82UL, that specification will guarantee that you do meet the autogas requirements. We're going to be asking the FAA to issue a letter clarifying that that is indeed true."

For its part, FAA is fully aware of the new specification (it had three people intimately involved in its development) but cannot rule on any certification issues until it is asked.