Avgas Alternative

Jan. 8, 1999

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.

"We're familiar with it," says Mark Rumizen of the standards staff at the FAA Engines and Propellers Directorate in Boston. "We're right on top of it, (but) whether or not we are going to give blanket approval to all the engines that have autogas STCs such that they can use the 82UL, I don't think we're prepared to give a definitive position on that right now. First of all, no one has asked for it....

"When they do ask for it, I understand there are grounds to maybe issue some sort of blanket coverage. But I'm not sure if we can do that, or how we can do that. That's something we're going to have to work out administratively with people like EAA and whoever wants to extend their STCs."

The introduction of 82UL as a replacement for 80/87 avgas is a little more problematic. At the outset of the specification process, committee members thought that the new fuel would be a direct replacement of 80/87 avgas.

However, it appears now to be not so clear cut. Motor gasoline stocks, from which 82UL will come, create a higher vapor pressure than is thought safe for low compression engines. However, explains Dr. Henry at Octel, vapor lock has been a major issue for use of this type of fuel in small aircraft for many years. It's one of the reasons oil companies aren't comfortable with their gasoline being used in that way. He says further that 82UL doesn't have to be more volatile. A producer can lower the potential vapor pressure of the fuel, but it would require a further or different refining step and that would be defeating the initial purpose of the specification, which was to make it easy for refiners to produce an aviation fuel.

While, according to EAA, some 70 percent of the single-engine fleet has an STC authorizing use of motor gas, it's the other 30 percent, which presumably uses 80/87 low lead gasoline, that accounts for the bulk of fuel sales. Thus, it's that 30 percent using 82UL that concerns the FAA.

"Vapor pressure is the key," says Rumizen at FAA. "You might run into a problem depending on the configuration of the fuel system. Vapor lock of the fuel (line) is a possibility."

As this is a brand new specification, nobody knows for sure what its impact will be. Indeed, after study and research the FAA could rule that 82UL could substitute for 80/87. Either way, the specification was designed for the future: a new generation of piston-engine aircraft.

"Essentially," Henry says, "as far as the subcommittee is concerned, this specification was written to encompass a new generation of aircraft on which Cessna is essentially taking the lead.... If the FAA chooses to say, ’Well, this fuel is good for any of the aircraft that are type certificated on motor gas,' that's fine, but that isn't our concern."

Looking ahead, subcommittee chairman Gonzalez thinks that FBOs now handling 80/87 fuel will have no trouble — should the market demand grow as he expects — switching their current low lead tanks to 82UL. There is nothing in 82UL, he says, that is not standard in motor gasoline with the exception of alcohol.

Gonzales further sees fuel jobbers downstream from the refineries and small refiners taking the lead in producing and distributing 82UL. "I think that when the market gets a taste of the cost differential, the rest is going to be history," he says. "It is going to be significantly less expensive. Even a little operator who decides to certify a truckload at a time, maybe between 7,000 and 10,000 gallon. He submits a sample of this fuel for analysis for which he can have an overnight response at small cost per gallon. Add another fraction of a cent for color dye and some for the paperwork. That's what you're adding to bulk motor gasoline. I would think that people are going to make a pretty good cut on the average with a fuel that will cost nearly a dollar less than avgas today... If my crystal ball is correct, I have a hunch that gradually there may be pressure to drift away from motor gas.''