Some airlines have been effective in reducing greenhouse gas emissions. "At Northwest, our greenhouse gas emissions have gone down 25 percent since 2000 and about 5 percent less than 1990," says Ken Hylander, Northwest's senior vice president of safety and engineering. "If Northwest was a country, we would be Kyoto [Protocol on reducing greenhouse gas emissions] compliant."

But emissions from the aviation industry as a whole continue to climb. According to the EPA, from 1990 to 2005 greenhouse emissions from military aircraft slid by 50 percent but those from commercial carriers rose by 16 percent, largely due to growth in the number of carriers.

Efficiency alone—even in the form of aircraft with improved engines and designs such as the Boeing 787, expected to deliver a 20 percent improvement in fuel efficiency over existing big airplanes—is not the answer. "A low-CO₂ fuel will help us to address that remaining portion of the pie," says David Daggett, technology leader for energy and emissions at Boeing. "That's why we're interested in biofuels specifically."

One such biofuel—ethanol—is already being used to power a heavily employed commercial fleet: piston-engine propeller crop dusters. Max Shauck, chair of the Baylor Institute for Air Science (who flew an ethanol-powered prop plane at air shows in the 1980s), has converted at least 1,000 such aircraft in Brazil, a country that has weaned itself from foreign oil by embracing ethanol domestically produced from sugarcane.

In addition to being easier on the engine, ethanol costs one quarter to one half as much as the aviation gas typically used in such propeller planes. Ethanol decreases the number of hours or distance such an aircraft can fly, however, due to its lower energy density, but "it develops more power and it's a greenhouse gas–neutral fuel," Shauck says. "There's plenty of ethanol produced in the world to power all the piston-engine aircraft."

The Federal Aviation Administration (FAA) is conducting tests but has yet to certify ethanol as a fuel for piston-engine planes in the U.S., says Lourdes Maurice, chief scientist and technical advisor to the FAA's Office of Environment and Energy. Regardless, ethanol's low energy density makes it unsuitable for jet-turbine engines. "Clearly we can't use ethanol," CAAFI's Altman says. "That's a blessing. We don't want to compete with food crops."

Diesellike fuel derived from plant oils might avoid that problem as well as supply similar greenhouse gas reduction (depending on how the plants are cultivated). Already, a Czechoslovakian L-29 jet—specially built in the 1960s by the Czech military to run on alternative fuels—flew for 37 minutes and reached an altitude of 17,000 feet (5,180 meters) powered entirely by reformulated canola oil. "Would you rather buy your oil from the Middle East," asks BioJet 1 copilot Doug Rodante, president of Green Fuels International (a company that promotes alternative fuels), "or the Midwest?"

But biodiesel solidifies into a gel at the cold temperatures found at high altitude, a fatal flaw for any aircraft fuel. The Czech jet has fuel heaters to get around this problem, and similar solutions could be engineered into other jet engines, argues physicist Rudi Wiedemann, president and CEO of Biodiesel Solutions, Inc., in Sparks, Nev., the flight's fuel provider.

Or the biodiesel itself can be further refined to ensure that it doesn't solidify until at least –40 degrees Celsius (–40 degrees Fahrenheit), the current standard for petroleum-derived jet fuel. UOP, a Honeywell Company, has developed such a "green diesel" by heating vegetable and animal oils to add hydrogen atoms to the long hydrocarbon chains, under the aegis of DARPA. In addition, its "ecofining" process adds kinks in the chains to prevent them from easily stacking—or gelling—at cold temperatures, producing a diesellike fuel with as much as twice the combustion quality of the petroleum-derived variety.

7 Comments

1. 1. David B. Benson 01:43 AM 1/15/08

   Perhaps a bit friendlier, but certainly not good for the climate. (1) The fuel is still about 1/2 fossil. (2) Contrails are bad.

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2. 2. dbiello 08:01 PM 1/15/08

   Very true Robert, as I note in the story. The key will be developing some kind of closed loop biorefinery system. But let's face it. The Air Force's goal is focused first and foremost on domestic sourcing and only secondarily on environmental benefit.
   
   And the airlines are just looking for cheap.

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3. 3. Inventhp 07:12 PM 1/22/08

   If contrails are an issue, and I think they are. Perhaps we should also be concerned about passenger mile per lb of H2O in the jet's exhaust. Perhaps this synthetic fuel is better in that regard. If it is not then perhaps the synthetic fuel should be used at ground level and continue to use conventional fuel in the jets.

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4. 4. biotele 08:33 PM 1/28/08

   Fly with hydrogen from Aluminum. The aluminum is regenerated by electricity:
   
   http://www.instructables.com/id/SODA-CAN-HYDROGEN-GENERATOR/

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5. 5. sam dobermann 08:02 AM 2/25/08

   Bring back dirigibles filled with helium. The Hindenberg was luxury liner after all. They can be designed more aerodynamically aand given enough motor power to go pretty fast and much less energy use. And less noise. And less room for runways, etc.

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6. 6. Thomas Boq 01:19 AM 4/11/09

   Tank water in the aircraft. Water does not burn. Water is the new fuel for the airlineindustry. Lead water through pipes to the engines. At the the jet engine before injection into jetstreamchamber where the air is compressed and hot, split before injection the water into hydrogen and oxygen. The inject the oxygen and water mix into hot compressed chamber of a jet engine. There it ignites and expand a lot like jet fuel. Water is a unlimited resource. It is cheap to exept in deserts by why not plan airports appropiate distance from waterresources. This way we could power any cars, busses, trains, ships, boats, bikes, aeroplanes.
   There is another solution too. That you ignite mixture of the oxygen and hydroxen without compressed air and let the expanded gas(water) thrust a jetturbine, use ax to transmit force.
   Third solution spilt water in engine let oxygen out, let hydrogen react with hot and compressed air in jetengine.
   
   The thing is to find a way to split water suffiently fast enought.
   The spaces ferries of NASA has engine-thrust from hydrogen.
   

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7. 7. Timberati 04:39 PM 7/17/10

   "[Brazil] has weaned itself from foreign oil by embracing ethanol domestically produced from sugarcane."
   
   Sugar cane ethanol is a fraction of Brazil's oil independence (~12% of Brazil's energy needs), much more of the credit goes to Petrobras for becoming better at extracting and refining oil (~88%).
   
   Brazil produces the oil equivalent of about 300,000 barrels per day of sugar cane ethanol, and its total oil consumption (according to the Energy Information Administration) is 2,500,000 barrels per day. Petrobras produces about 2,400,000 barrels per day of oil. In other words, 88% of Brazil's energy needs come from oil.
   

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