The Fight Over Avgas
Can private pilots fly unleaded?
- By David Freed
- Air & Space magazine, August 2013
Photo-illustration by Théo. Nozzles by Chad Slattery. Airfield © 2012 Marc Espolet / iStockphoto.
(Page 4 of 6)
Equipped with smaller pistons and combustion chambers, along with a gearbox, automobile engines function at high revolution speeds. Airplane engines are relatively lighter, with bigger cylinders that move comparatively slowly. That requires fuel with a higher octane rating to control what engineers call the “flame front” of the combustion process. A fuel’s octane rating indicates how much the fuel can be compressed before spontaneously igniting. The lower the rating, the lower the amount of compression a fuel can tolerate. When the fuel catches fire by compression rather than by a spark plug, knocking or detonation can occur, and uncontrolled detonation can destroy an aircraft engine in seconds.
That’s where lead comes in. It helps control detonation while preventing friction from forming between the engine valves and valve seats.
It’s not certain who discovered that adding liquefied lead to fuel increases octane rating (ethanol also boosts octane), but many credit the scientists at General Motors in 1921. By the 1930s, the U.S. Army Air Corps was routinely adding about three grams of tetraethyl lead to every gallon of fuel that its aircraft burned. Today’s most commonly used avgas has about two grams of lead per gallon and an octane rating of 100. (Some high-performance aircraft use avgas with an octane rating as high as 145.)
In 1990, Congress amended the Clean Air Act to mandate the removal of lead from all non-road vehicle fuels within five years. Fearing a meltdown of general aviation, lobbying groups determined that airplanes didn’t fall within the statutory definition of off-road vehicles and were thus excluded from the law. Work began in earnest to come up with an unleaded fuel. But more than two decades later, no one has yet introduced a reliable and affordable avgas replacement to the market.
That doesn’t mean ambitious entrepreneurs aren’t trying. Two small companies in particular—Swift Fuels of West Lafayette, Indiana, and Ada, Oklahoma-based General Aviation Modifications, Incorporated (GAMI)—are both confident they have hit upon a potentially viable unleaded fuel alternative.
Swift was born in 2005 as a privately funded, $6 million startup, with the goal of providing general aviation an affordable fuel that is “quasi drop-in”—it would require little, if any, engine modifications. The company today employs 10 people, including vice president of commercial operations Jon Ziulkowski, a type-rated commercial pilot who trained at Purdue University for a career in the airlines but ultimately found his life’s calling in developing aviation fuels.
Swift’s avgas formulation, UL102, also referred to as 100SF, mixes hydrocarbons to create go-juice that Ziulkowski says will provide piston-engine airplanes as much as 15 percent more range than standard avgas, per gallon. Swift hopes to open an industrial plant sometime this year that will produce up to 10,000 gallons of fuel components each month. After the fuel is tested and proven safe, says Ziulkowski, UL102 could begin hitting the general aviation market next year.
“It’s not an easy process, as we’ve discovered,” he says. “Redesigning infrastructure for avgas is very complicated.”