Wednesday, September 2, 2009

Is a 100LL Replacement Really Coming?

The latest issue of AOPAPilot Magazine arrived with an article titled Grass for Gas (members can access the online version at the link). The author tells of fueling his experimental-category RV-3, for a flight from Purdue University in Indiana to Frederick, MD, with SwiftFuel 100SF instead of our beloved blue 100LL AvGas. It apparently all worked out just fine.

There have been periodic stories coming out of Hoosier-land for a couple of years now detailing the progress of the alternative fuel from Swift Enterprises toward viability as a non-petroleum drop-in replacement for 100LL. Despite the adage about seeming "too good to be true", this story appears to get more credible with every news release and press item. This leaves me with a number of questions:

  • Who are these people?
  • What is this stuff?
  • Could this be for real?

Who are these people?

The wizard-in-chief at Swift Enterprises seems to be Dr. John J. Rusek, a Ph.D. chemical engineer with an impressive resume that includes lots of in-depth work in advanced propulsion systems, fuel technologies and catalysis.

Swift Enterprises operates under the aegis of the Purdue Research Foundation and has a small team of skilled people at work on the development of their alternate fuel technology. I'd say that they get full marks for credibility.

What is this stuff?

Swift Enterprises offered a very nice summary of the current status of their alternative to 100LL in a presentation at Oshkosh 2009. The slides are available in pdf format on their web site. That's a good place to get an overview.

Another very interesting source of information is the patent application filed on behalf of Swift Enterprises for their "Renewable Engine Fuel". The Abstract reads:

"The present invention provides fully renewable engine fuels derived completely from biomass sources. In one embodiment the fully renewable engine fuel is comprised of one or more low carbon number esters, one or more pentosan-derivable furans, one or more aromatic hydrocarbon, one or more C4-C10 straight chain alkanes derivable from polysaccharides, and one or more bio-oils. In addition, the fuel may contain triethanolamine. Such a lower octane renewable fuel may be utilized, for example, in automobile fuel, 100 LL aviation fuel applications, and turbine engine applications. These ethanol-based, fully renewable fuels may be formulated to have a wide range of octane values and energy, and may effectively be used to replace 100 LL aviation fuel (known as AvGas), as well as high octane, rocket, diesel, and turbine engine fuels. In another embodiment, there is provided a synthetic high octane aviation fuel comprising isopentane and mesitylene, and process of producing same from a biomass."

One table provides formulary information on a number of possible embodiments of the technology and includes an "AvGas 100LL Replacement". It consists of 13.1% ethyl acetate, 13.1% 2-methylfuran, 45.0% mesitylene (also known as 1,3,5 trimethylbenzene), 25.0% n-heptane, and 3.8% corn oil.

From the body of the patent, it seems that the first ingredient primarily increases the fuel's vapor pressure for good cold weather operation, the second and third ingredients contribute high energy content and octane-number enhancement, the fourth (a linear alkane) is actually a high-energy octane-number limiter, and the corn oil adds lubricity (we do have to pump this stuff).

This formulation is revealed by the patent application to offer a Motor Octane Number of 107 (compared to a minimum of 99.5 for 100LL, and about a 6.3% increase in heat of combustion per unit volume over 100LL. It is, however, 15.4% more dense than 100LL (i.e., about 6.9 lbs/gallon vs. about 6 lbs/gallon for 100LL). So if I filled N631S's 75 gallon tanks with this fuel I'd have on board as much fuel energy as I'd get from about 80 gallons of 100LL but I'd give up 70 pounds of payload.

(Let's note that this discussion is focused, for the moment, on the notional fuel formula from the patent app, and not the 100SF product being evaluated in engines today. The recent AOPA article mentions a fuel density for the recent product of about 6.5 lbs per gallon, so some evolution has been occurring.)

But based on the numbers from the patent, one pretty much has to conclude that, yes, Swift has got themselves a fuel that seems to meet the spec's for AvGas. The questions that remain are, will it work flawlessly as a drop-in replacement for AvGas? Only the torturous certification process will answer that. And, will it make economic sense?

Too good to be true?

The folks at Swift Enterprises seem, based on their descriptions of their production process, to be fond of sorghum as a feedstock. They say that it would take about 255,000 acres of sorghum to produce the fuel needed to replace all 100LL consumption in the US. To calibrate that for you, the Department of Agriculture says about six million acres will be planted in sorghum in the US in 2009 (down quite a lot from 10 or 15 years ago). This pales in comparison with the 80 million acres planted in corn. So, feedstock availability wouldn't seem to be a problem.

An acre of sorghum (again, according to USDA) yields about 64 bushels - presumably 128 bushels if it is double cropped. So, according to Swift's Oshkosh presentation (linked above) it will take about 33 million bushels of sorghum to cook up 300 million gallons of AvGas replacement. If sorghum goes for $3.00/bushel on the open market (not a bad number, historically) then the feedstock for a gallon of fuel would cost about $0.33. Even if the costs of manufacturing triple the costs of the inputs, the "refinery" price would be around $1 per gallon. Add in transportation and taxes and the $2.50 per gallon that Swift talks about would seem not unreasonable.

But, some folks suggest other problems may emerge. Back in March, AvWeb's Paul Bertorelli took a look at SwiftFuel and observed in part:

"Then there's the raw, commodity-driven blackhole of petroleum economics. The whole thing is tied to the price of oil which, at $40, isn't providing much encouragement for alternative fuel development. In the unlikely event that Swift Fuel proved cheaper on an equivalent octane basis than oil-based hydrocarbons, the refinery trade will buy up every drop of it for blendstock or otherwise bid up the price. One solution to this, says Swift's John Rusek, is to isolate the new fuel from the petroleum trade by marketing and distributing it through agricultural channels, as an aviation-only product. Well, maybe. Just because that hasn't been tried doesn't mean it couldn't work."

Well, oil is about $70/barrel these days and unlikely to spend much time below $50 in the future. So just maybe...

SwiftFuel has a lot going for it. A really smart technologist leading a solid team. A product that, so far at least, appears to perform and meet a need. No economic show-stoppers emergent to date. Positive test results in real engines in real airplanes. And a whole lot of pilots cheering them on. The next few years are going to be fun to watch and I, for one, am more hopeful than not.

See this June 2010 post for updated thoughts on the 100LL Replacement situation.


Comrade E.B. Misfit said...

Remember 82UL, or whatever it was that was supposed to replace 100LL?

I'll believe a replacement for 100LL is here when I see the fuel trucks loaded with it.

Frank Van Haste said...

Dear Miss Fit:

Your point about earlier mis-fires is noted and well taken. I think that the key difference (and advantage) in this case is that the fuels are compatible -- meaning that the transition can be gradual and nobody needs to put in a new tank farm.

That said, I too shall retain some degree of healthy skepticism.