Commercialization of Aviation-Grade E85 (AGE85)

University of North Dakota Energy & Environmental Research Center

Grand Forks, North Dakota – March 21, 2000

An ethanol-based alternative to aviation gasoline known as 100LL (100-octane low-lead) avgas,

AGE85 is:

88 volume% (vol%) ethanol

1 vol% biodiesel (must meet ASTM PS 121 specifications).

Developed and demonstrated by:

Great Planes Fuel Development, Brookings, South Dakota

South Dakota State University, Brookings

Lake Area Technical Institute, Watertown, South Dakota

Texas Skyways, Boerne, Texas

University of North Dakota Energy & Environmental Research Center, Grand Forks

Funding provided by:

South Dakota Corn Utilization Council

U.S. Department of Agriculture National Alternative Fuels Laboratory Program

Certified in May 1999 by U.S. Federal Aviation Administration (FAA) for use in Cessna 180 and 182 engine–airframe combinations.

Certified in February 2000 by FAA for use in any proportion with 100LL in certified engine–airframe combinations.

Three more engine–airframe FAA certification procedures ongoing.

Motivation

High-performance, high-compression, piston aircraft engines need high-octane fuel.

100LL is the last commercial fuel allowed by EPA to contain tetraethyl lead (TEL), 100LL contains four times the lead that used to be in automobile gasoline, and EPA wants to ban 100LL but is reluctant to until demonstration of a viable alternative.

Only three countries still produce TEL, and U.S. is not one of them.

In an oil shortage, 100LL would likely be first fuel with supply problems.

Some aircraft require even higher-octane fuel, and use of 100LL results in performance derating and/or shorter TBO (time between overhauls).

Engine overhaul is big flying expense, ranging from about $10,000 to $30,000.

Lead build-up in cylinders derates performance and shortens TBO, and toxic ethylene dibromide is often added to fuel to act as a lead scavenger.

Current general aviation market represents about 400 million gallons per year.

Why ethanol?

Excellent antidetonation properties – ethanol doesn’t "knock," even at high compression ratio.

Ethanol burns faster and at higher thermal efficiency than 100LL or gasoline, putting more energy into motion and less into heat.

Evidence for higher thermal efficiency – exhaust gas temperatures for AGE85 and 100LL are about equal, but cylinder head temperatures are much lower with AGE85.

The standard motor octane test method (ASTM 2700) doesn’t work for high ethanol-content fuels, because cylinder head temperature cannot be maintained at specified level.

Ethanol burns cleaner than 100LL, resulting in longer TBO.

Ethanol is currently cheaper than 100LL, which is selling at from $1.60 to $2.80 per gallon.

What’s required to make a viable ethanol-based aviation fuel?

Pure ethanol, with an Reid vapor pressure (Rvp) of 2.3 pounds per square inch (psi), does not vaporize well enough to start an engine.

Addition of pentane isomerate (Rvp of 15 psi) at 11% yields a fuel with an Rvp of 7.5 psi, which provides good engine starting (even in South Dakota winter) and does not cause vapor lock.

Comprising about 88% isoparaffins, 5% cyclics, 7% paraffins, and no olefins, aromatics, or sulfur, pentane isomerate is ideal additive. Current FAA-certified aviation gasolines contain about 50 to 60% isoparaffins and paraffins, 20 to 30% cyclics, up to 20% aromatics, and usually no olefins. Under conditions of use in aircraft:

Because of its higher viscosity and lower vapor pressure, addition of biodiesel at 1% is sufficient to maintain a thin film of biodiesel on relatively cooler cylinder wall and head surfaces to protect against corrosion. In a 12-week Society of Automotive Engineers test with two different aluminum alloys (356 and 5052), corrosion weight losses for AGE85 and two commercial 100LL products (A and B), were:

For 356 alloy: 2, 18, and 20 milligrams per square centimeter (mg/cm²), respectively.

For 5052 alloy: 19, 33, and 30 mg/cm², respectively.

AGE85 Performance

Engine performance was measured on AGE85 and 100LL using a Lebow torque meter in a static ground test. Figures 1 and 2 show that both torque and horsepower are increased at any power setting when using AGE85 versus 100LL. The largest increases tend to occur at lower to medium range power settings. For example, at 22 inches of manifold pressure and 2000 rpm, torque and horsepower increase 12% and 13%, respectively, while at higher power settings of 26 inches of manifold pressure and 2200 rpm, increases in torque and horsepower are 9% each. These results indicate that at common cruise power settings, AGE85 provides a significant advantage in terms of available torque and horsepower. At higher to maximum power settings, the percentage differences tend to be much smaller; thus, no significantly greater stresses are placed on the engine during maximum power maneuvers, like takeoff.

At 81,000 Btu/gallon, AGE85 has 28% less energy than 100LL (at 112,000 Btu/gallon), but because of higher thermal efficiency, only about 12 to 15% higher fuel flow rates were observed for equal power settings on AGE85 and 100LL.

Commercialization

Certification proceedings are in progress for three more engine–airframe combinations, one of which includes a supercharged engine.

An AGE85 fuel specification based on ASTM guidelines is being finalized.

AGE85 is currently selling at $1.30 per gallon in Madison, South Dakota.

Often in response to initiatives by pilots throughout the U.S. and Canada, talks are ongoing with several potential blenders and distributors.

A paper titled Design of "Ethanol-Based Fuels for Aviation" will be presented at the General Aviation Technical Conference in Wichita, Kansas, on May 9–11.

More information:

Ted Aulich 701-777-2982 or taulich@eerc.und.nodak.edu

Dennis Helder 605-688-4994 or

Jim Behnken 605-868-3188 or 605-882-6311