As a result, the Air Force—and other military branches as well as the Defense Advanced Research Project Agency (DARPA)—have begun to experiment with alternatives. "Alternative fuels offer the potential, if not to lower the price [of petroleum-derived fuels], at least to provide a hedge in the future against their future growth or, put differently, their volatility," says technologist Douglas Kirkpatrick, DARPA's program manager for alternative fuels efforts. "The key here is to go from one source to many."
He adds: "Anyone who runs a business knows that you don't want to have one supplier. Essentially, that's the position we're in."
In the short term, the Air Force hopes to make use of the Fischer-Tropsch chemistry that kept Nazi-era Germany and the apartheid-era Union of South Africa's airplanes flying in the absence of oil (and still supplies 40 percent of South Africa's transportation fuel needs) to ensure diversity of supply. In addition to flying the C-17 across the country—a plane powered by the same Pratt and Whitney F117-100 engine employed on commercial Boeing 757s—the Air Force in August certified its still flying 1950s-era B-52 bombers to burn synfuel.
"Why start with an old weapons system?" Anderson says. "It's a very simple engine compared to newer ones, less things can go wrong."
The natural gas-derived synfuel performed perfectly in both planes during ground tests, flights and even during cold starts in the dead of winter in Minot, N. Dak. The 50–50 blend of synfuel and JP-8 fulfilled all 40 of the Air Force's fuel performance criteria, including coming through in extremely high and low temperatures. "Pilots are telling us that they're feeling no difference at the controls between the fuels," Anderson notes.
Fischer-Tropsch synfuels promise to provide a potentially cleaner fuel supply as well. Burning the purer fuel—clearer than petroleum-derived kerosene—eliminates sulfur emissions that lead to acid rain and reduces (by 50 to 90 percent) the amount of tiny particles that usually remain after combustion, according to Richard Altman, executive director of the Commercial Aviation Alternative Fuels Initiative (CAAFI), an industry effort to develop new energy options.
But synfuel will not lead to fewer emissions of carbon dioxide, the greenhouse gas primarily responsible for global climate change. Environmental group the Natural Resources Defense Council estimates that turning coal to liquid fuel emits twice as much carbon dioxide as producing petroleum fuels. "We will only buy fuel that is greener than our current alternatives," Anderson says. "Our current alternative is petroleum-based jet fuel."
The European Union plans to restrict carbon emissions from airplanes beginning in 2012; in the U.S., legislation is pending that would impose similar limits, and five states (California, Connecticut, Pennsylvania, New Jersey, New Mexico and New York) have petitioned the Environmental Protection Agency (EPA) to regulate such emissions in the interim. "We now know that the solution that will be most environmentally acceptable," CAAFI's Altman says, "will have significant biofuels."
The amount of emissions from aircraft compared with other vehicles is relatively small—roughly 3 percent of total worldwide greenhouse gas emissions from fossil fuel burning, according to the U.N. Intergovernmental Panel on Climate Change (IPCC)—nonetheless it has a major impact on the climate. By releasing carbon dioxide higher in the atmosphere, airplanes allow the molecule more time to trap heat, also contributing via contrails and other chemically active gases, the IPCC notes.