10 September 2008--A series of flight tests by the U.S. Air Force late last month using a synthetic jet-fuel blend comes at an awkward time for the service. Part of a two-year-old program to integrate domestically produced, non-petroleum-based jet fuels into the Air Force's fuel supply, the tests included an F-22 Raptor, which underwent the first aerial refueling using a synthetic jet fuel, and an F-15 Eagle, which became the first fighter jet to fly at Mach 2.2 on synthetic fuel. However, the departures of two key supporters of the synthetic-fuel program have cast doubt on its future and the likelihood that the service will become as aggressive a promoter of the petroleum substitutes as it had stated in the past.
Much of the impetus for the certification and proposed adoption of synthetic fuels came from William Anderson, the assistant secretary of the Air Force for installations, environment, and logistics. But a little over a month ago, he resigned, citing a lack of support for his plans. Anderson's departure followed the exit of Michael Wynne, the former secretary of the Air Force who initiated the program and was forced out of office in June after security lapses were found in the Air Force's handling of nuclear weapons. The two officials had spoken widely about a goal to certify all Air Force airframes to fly on synthetic fuels by 2011 and to fly half of its North American fleet on a blend of domestically sourced synthetic fuel by 2016.
Skeptics have long questioned the service's ability to meet that latter goal, which hinges on enticing commercial partners to build production plants to supply the fuel. The alternative fuels pursued by the Air Force are intended to perform identically to ordinary JP-8 jet fuel, which is the kerosene-based fuel most commonly used in Air Force aircraft. The key difference with a synthetic fuel is its source. A vast number of feedstocks--including natural gas, coal, and biomass--can be converted into a usable fuel with a method called the Fischer-Tropsch process. In all its test flights to date, the Air Force has used fuel derived from natural gas. ”We're hoping that our promise to purchase the fuel will be enough for a few companies to find financial backers and build a plant,” says Tim Edwards, the head of fuels technology at the Air Force Research Laboratory, in Dayton, Ohio.
This past January, the Air Force issued a call for companies to build a coal-to-liquid plant on land leased by Malmstrom Air Force Base, in Montana. With a new acting secretary of the Air Force, however, the fate of this plant is up in the air, with no decision expected until the end of the year. Any delay in building a production facility would make it very difficult to meet the 2016 goal, say experts.
Synthetic fuels are not unknown in aviation; South African Airways has been flying on a synthetic jet-fuel blend since 1999. But there are only a handful of production plants in operation around the world, even though the ability to make synthetic fuels has existed for half a century. Given that the Air Force pays an extra US $660 million for every $10-per-barrel increase in the cost of oil, the idea of cultivating a domestic market for jet fuel has immediate appeal. ”You just can't get away from the looming demand of China and India,” says Richard Lawson, a retired four-star Air Force general and former president of the National Mining Association. ”I think you can make a terrific case for helping the country to accelerate the development of any alternative source of energy if it reduces the risk that our needs for energy would come into conflict with others' needs for energy.”
Synthetic fuels have long been considered more expensive to produce than petroleum-based jet fuels, and making them emits twice the amount of greenhouse gases as making ordinary jet fuels, according to an estimate from the National Renewable Energy Laboratory, in Golden, Colo. To assuage concerns over the emissions associated with synthetic-fuel production, an energy law passed in 2007 included a provision mandating that the Air Force not purchase any alternative source of fuel whose environmental profile is worse than that of the fuels it uses now. A report published this year by a Defense Science Board energy-security task force expressed ”strong concerns” about the viability of synthetic fuels, citing high production costs, a high level of initial investment needed from industry, and the untested nature of carbon sequestration, which would be a necessary component for any coal- or natural gas–based fuel to qualify.
But the fuels might be more affordable than people once thought. A 2007 report from the National Energy Technology Laboratory (NETL), in Morgantown, W.Va., concluded that a $5 billion investment in a commercial-scale coal-to-liquid facility located near coal deposits would pay itself off with oil priced at just $61 a barrel, including the cost of equipment to capture and compress carbon dioxide for injection into a pipeline. The estimate does not include the cost of burying the carbon dioxide or transporting the fuel to its markets. (According to Daniel Cicero, the technology manager of the fuels division at NETL, a conventional petroleum refinery becomes economical with oil at about half that price.) At least two synthetic-fuel production facilities now being planned in the United States, by Rentech and Baard Energy, intend to capture carbon dioxide that is released during the synthesis process and use it in enhanced oil recovery by injecting it into nearby oil fields.
While the future scope of the program remains in limbo, the certification process continues apace, with test flights scheduled for this fall to collect data on coal-derived jet fuel. Before any flight test, the fuels are subjected to months of examination. An attractive fuel must have certain properties--among others, it needs to have an energy density similar to that of conventional fuels and thermal stability at the temperature ranges that aircraft face, in particular a similar freezing point. While Fischer-Tropsch fuels come close, blending them with conventional jet fuel lands them within the acceptable range for those properties.
Another aspect under test is ”O-ring swell.” Ordinarily, jet fuel causes certain connectors among aircraft parts to swell up, but Fischer-Tropsch fuels don't have that property. To make sure that no unexpected leaks appear when switching from one type of fuel to another, the engineers at the Air Force Research Laboratory carefully monitor the behavior of O-rings when they're in contact with synthetic fuels. ”We spend all this time and money testing components that are a dollar apiece,” Edwards says. ”You wouldn't think it would be such a big deal, but there are millions of them across our aircraft. If it turned out that we had to replace all of them to use synthetic fuels, this program would be a nonstarter.”
Going forward, the lab intends to test samples of more speculative and environmentally attractive sources for jet fuel, including algae and seaweed. If the Air Force backpedals from its synthetic-fuel push, commercial airlines--which have dabbled in biofuels--may be the only ones left to pick up where the Air Force leaves off.