|Air Force Holds Throttle on Future of Green Jet Fuel, Popular Mechanics, December, 2009|
RIVERSIDE, Calif. -- It's a piping hot late-summer morning, so there's a sense of relief when the KC-135 Stratotanker launches off the runway to leave the heat--and expensive jet fuel--sweltering in the distance behind. I'm strapped in the back on our way out of March Air Reserve Base here for a mission that will bridge the Air Force's past and future: This 50-year-old tanker is a workhorse retrofitted with advanced avionics and little else, but it's about to rendezvous with a supersonic $142 million F-22 Raptor, a multirole stealth fighter that's just taken off from Edwards Air Force Base with a belly hungry for fuel.
I'm laying on my own belly, peering out of a small window at the tail of the KC-135 as the F-22 gradually approaches for a fill-er-up. The stealth fighter's sweptback wings overwhelm our field of vision, and I can see its pilot just overhead. A technician wields a joystick to manipulate the 18-ft. boom, which extends to deliver fuel to the Raptor. At 22,000 ft., the F-22 maintains its rock-steady speed for a robotic alt-fuel handoff that's equal parts Top Gun and International Space Station. Midair refuelings between Stratotankers and Raptors, after all, have become high-tech routine. But today's encounter is historic: For the first time, the fuel in both planes is a 50 percent synthetic blend. And for all this flight means to the Air Force's role at the forefront of alternative energy in aviation, it's over within a few minutes--the conjoined planes separating, the F-22 lingering for a moment before banking right and falling away.
Once the KC-135 is back on terra firma, the tanker pilots report that the synthetic-fuel blend felt exactly the same as standard JP-8, and their impressions are later supported by downloaded data. We also learn that transient throttle maneuvers and supersonic speeds in the F-22 were indistinguishable from those of a typical flight. The test appears to be a success.
Synthetic fuels may seem like a pie-in-the-sky solution to the current oil crunch, but the technology is nearly as old as modern aviation. In the 1920s, chemists Franz Fischer and Hans Tropsch developed the "Fischer-Tropsch" process, which produces synthetic fuel from nonpetroleum sources including coal, natural gas or biological sources. The technique was used to create synthetic fuel in Germany during World War II after the Nazis lost access to crude-oil supplies. Decades later, the technology resurfaced commercially in South Africa as a way to cope with international sanctions.
The U.S. Air Force cites environmental concerns, energy security and energy independence among its reasons for adopting synthetic fuel technology, but the bottom line is glaringly obvious to anyone who's paid high prices at the pump: Every $10 increase per barrel of oil results in a $600 million per year increase in fuel costs for the Air Force. The uncertainty of the global oil market only boosts the incentive to develop alternative fuels, like synthetics, that can be used without modifying existing airplanes.
Consumption levels of synthetic fuel are identical to standard fuel, but synthetics burn more cleanly, as their sulphurless composition produces less soot and particulate matter. Maintenance is reduced because combusted fuel leaves fewer engine deposits. The fuel leaves thinner contrails, offering visual evidence of the fuel's cleaner burn characteristics. But the process does produce carbon dioxide during manufacturing--and, oh yeah, when it burns.
Former Air Force Secretary Michael Wynne spearheaded the agency's investigation into alternative fuels in 2005 by creating an 11-member task force. Just a year and a half later, a B-52 Stratofortress flew out of Edwards Air Force Base on 50 percent standard-issue military JP-8 fuel and 50 percent Synthetic Paraffinic Kerosene fuel derived from natural gas. (Unlike petroleum products, the synthetic fuel lacks aromatics, preventing it from being used in ratios greater than 50 percent.) The B-52 was the perfect candidate for testing, since its eight engines offer ultimate mechanical redundancy; the first flight was performed with only one engine using synthetic fuel, so that if the engine failed there would be seven backups.
"We tested the crap out of the B-52 engines before we flew it," explains Jeff Braun, director of the Alternative Fuels Certification Office. "We did component tests on the engines, ground tests, engine install ground tests and then single-engine flight tests. We then stair-stepped from one, to four, to all engines, which provided a component of risk mitigation." The testing process has trickled across the entire Air Force fleet, with future efforts encompassing UAVs, helicopters, ground-support equipment and each variant of the F-35 Lightning II. "We're really just trying to establish a market," insists Betty Rodriguez, subsystems technical advisor for the Air Force's Flight Systems Engineering Division. "We're the consumers, not the producers."
Though the process of validating and testing synthetic-fuel blends continues within Air Force and civilian circles, its future is fraught with question marks. At least for the time being, the Air Force has been sourcing its natural gas-derived fuel from the Shell Corporation in Bintulu, Malaysia. (The U.S.-based Syntroleum Corporation, which supplied fuel for the B-52 flight, completed research and limited production at a pilot plant for synthetics but won't open a full-scale facility until early 2010.) The Air Force will also be sourcing 5000 gal. of synfuel from Rentech in Colorado.
Prices currently hover at around $3.04 per gallon, which is roughly the same price as standard JP-8, although transportation fees of roughly $4.60 are added to either fuel. "You have to realize we're talking about relatively small research and development quantities," Braun explains. "I'm buying a couple hundred thousand gallons. Who knows what kind of price I'd get if I were buying a couple hundred million gallons?"