The Next Biofuel Frontier: Jet Engines
http://www.popularmechanics.com/science/space/4299105
In the race to power planes with plants, airlines have begun test-flying a gamut of options, including the oil from algae, jatropha and camelina. From a technical perspective, it may not matter which biofuel wins, so long as there are ample contenders.
BY DAVIN COBURN
In a test last Wednesday in Houston, Continental became the first U.S. airline to test synthetic paraffinic kerosenes--otherwise known as jet biofuels. Engineers filled one of the Boeing 737-800's twin engines (which required no modifications) with a 50/50 blend of oils from jatropha and algae and regular Jet A1 fuel. During the 90-minute flight, pilots turned the engine off and on and abruptly accelerated and slowed down the aircraft. The biofuel performed flawlessly--and even appeared to get better fuel economy than the engine running off traditional Jet A1.
"We are thrilled with the flight on Wednesday," says Jennifer Holmgren, general manager of renewable energy and chemicals at UOP, a division of Honeywell, which produced the fuel. "We'll have the detailed data in the next few weeks, but the initial feedback is very promising"
As valuable as the test could prove for Continental, it's also a major step forward for pond scum. UOP also manufactured the biofuel that Air New Zealand tested in December, a 50/50 mix of conventional fuel and oil from the seeds of jatropha--a drought-resistant plant that grows well in arid regions. Only 2.5 percent of Continental's fuel blend came from algae, scraped off a pond in Hawaii by supplement company Cyanotech and processed for oil. But because algae can yield 10 times more bioenergy molecules per area than any terrestrial plant--and it doesn't compete with cropland--the Scripps Institution of Oceanography recently dubbed it alternative energy's "green bullet."
"Algae has tremendous potential for the production of billions of gallons of jet fuel," Holmgren says. "Proving its use as a source for jet fuel now is essential to keeping up the momentum and developing the technology to harvest and process the quantities that will be needed."
The International Air Transport Association wants its 230 member carriers to be using 10 percent alternative fuels by 2017; the European Union will cap airline carbon-dioxide emissions in 2012. These looming deadlines have helped prompt increased testing, even as the price of gasoline retreats from its high of $4.36 per gallon last summer. With the latest milestone, Boeing estimates a regularly scheduled passenger flight could be powered by a biofuel blend in three years.
Airline tests thus far have been limited to 50/50 blends. Partly, that's because the widely used Fischer-Tropsch production process for bio-jet fuels eliminates aromatics. The hydrocarbon rings help swell some types of elastomers in aircraft fuel systems, ensuring no fuel leaks. Eliminating conventional fuel entirely, and thus petroleum-based aromatics, is a bone of contention in the industry--so for purposes of expediency, a 50/50 blend has a higher chance of being certified by ASTM International, which approves all the jet fuel used in the United States. Partly, however, the choice to blend is a financial one, because bio-jet fuels have proven to work fine without blending in any conventional fuel at all. As part of a DARPA contract in 2006, UOP created a 100 percent alternative Jet Propellant 8 (JP-8) for the military, which included aromatics UOP added by refining pyrolysis oil derived from solid biomass. It was just incredibly expensive.
The aviation industry currently burns through nearly a quarter-billion gallons of jet fuel daily, so one key to cost effectiveness will be diversification. Experts expect algae could become a viable source in the next eight to 10 years--and in the meantime, other feedstocks will get their turn in sun. Japan Airlines, which plans to conduct the next biofuel test flight at the end of this month, will run an airliner with a blend of camelina oil and conventional fuel. Oil from jatropha and camelina plants could be viable in commercial quantities in the next three to five years. "When broken down to oil, different biofuel feedstocks have the same chemical compounds and are virtually indistinguishable from each other," Holmgren says. So they can be mixed and matched in any ratio necessitated by supply.
"There is still work to be done," Holmgren says, "but this demonstration flight helps to illustrate that it is worth the effort."
