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.