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When the Navy F/A-18 jet called the Green Hornet takes off over the Chesapeake Bay on Earth Day, it will aim to break a barrier that has proven far more durable than the speed of sound.

The twin-engine tactical aircraft is prepared on April 22 to make a supersonic flight on biofuel—its tanks filled 50 percent with oil refined from the crushed seeds of the flowering Camelina sativa plant. The test flight at the Naval Air Station at Patuxent River, Maryland will be a milestone in the Navy’s efforts to reduce its reliance on petroleum, and perhaps, in the elusive search for an alternative fuel for aviation.

The event is meant to showcase the Pentagon’s efforts to increase use of renewable energy, not only as a climate change initiative but to protect the military from energy price fluctuations and dependence on foreign oil. When President Obama announced his offshore drilling and energy security plan last month at Andrews Air Force Base, he used the Green Hornet as a backdrop. As naval aviation’s biggest fuel consumer, the F/A-18 Super Hornet is a fitting test aircraft.

Secretary of the Navy Ray Mabus has set a target that half of naval energy consumption will come from alternative sources by 2020. A “Great Green Fleet,” to sail by 2016, will include nuclear ships, as well as surface combatants with hybrid electric power systems using biofuel and biofuel-powered aircraft.

But for now, the Navy is seeking only to certify its first blend of biofuel and petroleum, by showing it can be used for the Super Hornet’s full range of flight operations. That includes demonstrating that the alternative fuel can deliver the power needed to fly faster than the speed of sound (343 meters per second).

Petroleum Paradigm

“One of the challenges we’ve had is that everything we have ever used in naval aviation has been designed around petroleum-based fuel,” says Rick Kamin, the civilian who leads the Navy’s fuel program. “[The engine] is taking advantage of everything that a petroleum-based fuel provides. We’ve had to work to break down that paradigm.”

Case in point: Engine seals. They were designed under the assumption that the engines would run on petroleum jet fuel, which contains aromatics—certain very stable compounds—that cause seals to swell, preventing leaks. After months of testing, the Navy concluded that current engine seals still need a certain amount of petroleum.

“One of our primary objectives is that the fuel we approve from non-petroleum sources has to be a drop-in replacement,” Kamin says. “It has to perform the same as a petroleum-based fuel performs and require no modification to the aircraft. Our goal is that these fuels have to be invisible to the operator.”

One of the appeals of Camelina oil, in fact, was that despite the aromatics issue, the fuel made from it was remarkably similar to the military petroleum jet fuel called JP-5. The biofuel developed by Sustainable Oils of Seattle has the same energy density. Not only does it deliver the same power, but all the aircraft systems—including the fuel gauge, which reads energy density—can operate on biofuel just as they would on conventional jet propellent.

“All we’re doing is what nature does over millions of years,” says Tom Todaro, chief executive of Sustainable Oils. “Jets today are flying on biomass—it’s just that with pressure and time, the oxygen has been leached off the oil and replaced with hydrogen. All we did was, using molecular biology and chemistry, make that move at a much faster speed.”

Without the work in the laboratory, wild-growing Camelina would not easily squeeze out a type of oil with the oomph to power military flight. A member of the mustard family and a relative of canola plants, the heavily-branched Camelina looked like a good biofuel source because it produces copious small seeds with high oil content. But Sustainable Oils and its two parent companies, agricultural science firm Targeted Growth and Houston-based biofuel producer Green Earth Fuels, spent a decade and millions of dollars breeding a strain of seed optimized for fuel production. The company won contracts valued at $18 million from the Defense Department last year.

Crop Science

The company is confident that it has overcome many of the disadvantages of the corn- and soy-based biofuels now in commercial use, like ethanol and biodiesel. Camelina is cold-tolerant, needs little water or fertilizer, and can be rotated in the northwestern United States and Canada on fields that farmers otherwise would leave fallow between wheat crops. “We wanted a crop that didn’t compete with food,” says Todaro. The company points to a lifecycle analysis conducted by scientists at Michigan Technical University concluded that the Camelina-derived jet fuel would produce 84 percent lower carbon emissions than petroleum fuel.

Sustainable Oils is just one of several companies working with the Department of Defense in the search for military-grade biofuel. Solazyme of South San Francisco, California has contracts to provide algae-based fuel to the Navy for testing in ships as well as aircraft. Houston-based Accelergy last month announced it has begun production of a synthetic jet fuel from coal and biomass to be evaluated by the Air Force.