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Researchers have been looking far and wide for biofuel sources, including switchgrass. (University of Wisconsin)

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Richard Branson and Boeing heap hope-and hype-on biofuels.

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Aviation entrepreneur Richard Branson recently demonstrated what kind of leverage is available to an ecologically friendly and media-savvy billionaire. He did this, as he always does, by putting his venture capital where his mouth is.

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In April the CEO of Virgin Atlantic Airlines and Virgin Fuels agreed to buy at least 15 Boeing 787 Dreamliners, but the $2.8 billion-plus deal came with a catch: Virgin’s fuels division, Boeing, and General Electric had to form a partnership to test alternative fuels in 747s next summer. Last year Branson founded Virgin Fuels and pledged $400 million over three years for its renewable energy and efficiency projects.

Branson’s bold moves may quicken the pace of research to find environmentally friendly fuels for aviation. It is not a matter of will—airlines, airplane manufacturers, and military agencies all want to make aviation greener—but of engineering: finding a secure and more predictably priced fuel source and refining it to produce energy efficiently. The challenge is daunting; in the United States alone, about 60 million gallons of jet fuel burns each day.

Today, airplanes burn less gas per mile than ever, but Boeing predicts air travel will double by 2020. Aviation will have a much bigger effect on the environment, and incur much higher fuel bills, unless a source of alternative fuel helps shrink costs.

While airplanes are responsible for only about three percent of human-related greenhouse gas emissions (cars and power plants produce far more), scientists charge that the industry contributes six to 12 times more to global warming than the other sources. That’s because airplane emissions occur mainly at high altitudes, where greenhouse gases last longer, says Robert Hendricks, a scientist at NASA’s Glenn Research Center in Cleveland, Ohio, where the agency is working with the Air Force and others to investigate new fuels. Airplanes also leave contrails and cirrus clouds, which trap heat.

But which alternative energy source—soybeans, algae, leftover fat—is best? And can one sole contender fit the need?

Traditional aviation gas known as Jet-A, or the military version, JP-8, is some of the most prized stuff to be derived from a barrel of oil, the petroleum version of fine wine. It’s refined to almost pure hydrocarbon energy, packing more energy per pound than most other fuels. It also flows easily at the frigid temperatures of high altitudes and remains chemically stable—at low risk of explosion—at high temperatures.

Standard alternative fuels don’t stack up. Ethanol, for instance, packs far less punch: To get the same amount of energy, an airplane must carry about 65 percent more ethanol than jet fuel. The additional weight necessitates larger wings and engines, which in turn demand still more fuel. Then there’s biodiesel, which turns the consistency of Vaseline at cold temperatures. Liquid hydrogen isn’t a great option, because it has to be carried in heavy cryogenic tanks, a requirement that forces airplanes to burn more fuel to stay aloft—especially when groaning in slowly for landings.

Although an unmanned jet powered by a hydrogen fuel cell flew over Switzerland this year, today’s fuel cells—which generate electricity by combining the charged particles of hydrogen and oxygen—lack the power to run anything more than a small aircraft.

But Boeing has hopes of replacing the auxiliary power unit generators with more efficient fuel cells that produce little or no pollution, even when running on jet fuel, in order to power the electrical systems on commercial airplanes.

There is one existing alternative jet fuel, made from coal or natural gas through what’s known as the Fischer-Tropsch Process. It was pioneered in Germany during World War II when oil was in short supply and later in South Africa when that nation was ostracized by oil-producing countries for practicing apartheid.

Fischer-Tropsch fuel burns cleaner than traditional jet fuel, spitting out up to 90 percent less of the particulate pollution that muddies the air and causes health problems. The fuel also leaves engine parts clean and shiny instead of blackened with soot. And it soaks up more heat, freeing airplanes from the requirement of weighty vents to get rid of the heat as they fly.

The trouble with Fischer-Tropsch, environmentally, is that the process of making it—turning coal to gas, then gas to liquid—releases nearly twice as much greenhouse gas as regular jet fuel does over its life cycle. Researchers are trying to figure out how to sequester excess carbon dioxide gas, possibly by capturing it and storing it underground.

In December 2006, the Air Force, which guzzled nearly $6 billion worth of jet fuel last year and wants to convert half its fleet to synthetic fuel (based on natural gas or coal) by 2016, used a B-52 to test Fischer-Tropsch fuel made from natural gas.

But to be of any use, Fischer-Tropsch fuel production must be scaled up dramatically, says Richard Altman, executive director of the Commercial Aviation Alternative Fuel Initiative, an alliance of airplane manufacturers, airports, and airlines formed last year.

Altman spent nearly 40 years as an engineer at Pratt & Whitney and recalls a small band of chemists who quietly toiled for years over fuel blends, hitting up division heads for funding. Now, suddenly, they’re in the spotlight.

“They…became rock stars after being people with tin cups who went around asking for money,” he says.

Bill Glover is managing director of environmental strategy at Boeing Commercial Airplanes and a founding member of the Commercial Aviation Alternative Fuel Initiative. Glover’s first project at Boeing as a young Purdue graduate was developing a quieter hydraulic system for the 707.

Ever since, he has looked for ways to make aviation cleaner and quieter and says the company has been all for them: “I have asked to do things and nobody ever said ‘no.’ ”

When they invited a few experts on the subject of alternative fuels to a meeting at Boeing’s Seattle facilities last year, even Glover and his colleagues were skeptical about alternative fuels being practical for airplanes. But the meeting got people’s hopes up: “The word got out and we started getting phone calls from other people who wanted to be there and it grew and grew,” he says.

They turned out to have a full-fledged conference; that’s where the alternative fuel initiative came together. The group’s aim is to lean on fuel producers, urging them to put more effort into developing alternative fuels for aviation.

Members of the initiative are also drawing up standards for alternative fuel blends, so the Federal Aviation Administration can promptly certify the formulations for use. “We formed a posse,” Altman says. “Everybody raised their hands and said ‘I’m in.’ The level of cooperation has been unprecedented.” The initiative doesn’t have much of its own money to spend, but it’s propelling plenty of spending by the FAA and others.

The Transportation Research Board is calculating how a shift to alternative fuel will affect an airport’s economics and the FAA is paying for an environmental review of alternative fuel options. The initiative has set a goal of having a biofuel blend for jets approved by about 2016.

Oils from plants are most often cited as sources for alternative aviation fuels. But growing and delivering enough product to satisfy the fuel demand might be self-defeating.

The production and use of fertilizer, the need for long-distance hauling, and the operation of processing facilities might cause more ecological damage than it prevents.

“You don’t want to spend more energy trucking low-energy material around to get it to your plant than you end up in the fuel you produce,” says Douglas Kirkpatrick, who oversees biofuel projects for the Defense Advanced Research Projects Agency, or DARPA,which is spending more than $15 million on at least three aviation biofuel projects.

A team of researchers working for NASA calculated that a field of soybeans, a common biodiesel crop, big enough to cover Florida would replace merely 15 percent of the U.S. commercial jet fuel burned each year.

Even if such a harvest were practical, the soybeans would be taking away land for higher-value crops, including food plants, and thus driving up those costs.

But there may be other options. Researchers in Brazil are experimenting with a jet fuel that is made from the nuts of the babassu palm, a tree that’s already growing across millions of acres there.

The U.S. Department of Energy also studied algae, which grows quickly and densely while sucking up carbon dioxide, producing 150 or more times as much oil per acre as soybeans.

If algae were grown on a large scale at a reasonable cost—a scenario still in the works—an algae patch the size of Maryland might supply 85 billion gallons of fuel a year, enough for the world’s entire jet fleet.

Then there are fats. William Roberts, a professor at North Carolina State University, helped develop a patented process to turn fat-rich animal and vegetable oils into jet fuel.

A big advantage of Roberts’ “flying fat” system, called Centia, is that it uses any source of fats, including cooking grease or animal renderings, which are typically cheaper than corn or canola oil. The process strips out fatty acids, then converts them into straight chains of hydrocarbons that engineers can break into smaller, branched molecules in just the right mixture for jet fuel.

So far Roberts is at only “the teaspoon level” of fuel production, but based on the current prices of fat, he thinks Centia could scale up affordably. Whatever the new fuel is made from, the stuff will have to be indistinguishable to airplanes and their engines.

Anything that requires rebuilding the world’s airplane fleet or renovating every single airport would be an instant no-go. “There’s billions of dollars invested in jet engines,” Roberts says. “Manufacturers are saying ‘We’re not going to make engines that burn your fuel. You’re going to make fuel that runs in our engines.’ ”

There may be no one perfect fuel crop, though. The choice of fuel may depend on where certain crops grow best. “Our vision is, if you go to New Zealand, you get biojet from algae and then you go to Iowa and get biofuel derived from soybeans,” says Boeing’s Bill Glover. “Then you fly to Texas and use straight Jet-A.”

The key will be whether alternative fuels can be turned out in large enough volumes to make their per-gallon price affordable. For example, making JP-8 from biodiesel today isn’t very efficient; the jet fuel contains only about 30 percent of the energy of the original.

“The engineering challenge is not a question of ‘if.’ It’s ‘Are we going to do it at $1.50 a gallon or $2.50 a gallon,’ ” says DARPA’s Kirkpatrick. “It’s a question of what corners can we cut and what innovations are we able to find to do it efficiently.”

The larger challenge may be one of matching good intentions with economic, mechanical, and chemical realities. Some of the early investments and research may go nowhere, but looking back, future generations will at least be able to say that the aviation world was trying.

They might joke about how silly it seemed to try running airplanes on soy when animal fats are so widely available, lament the lost possibilities of the Babassu palm, or simply wonder how oldtime avgas used to smell.

About Michael Milstein

Michael Milstein is a freelance writer who specializes in science. He lives in Portland, Oregon.

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