The use of jet fuel from renewable sources is now well demonstrated, but it costs more than double what fuel made from petroleum does, according to airlines, aircraft companies and suppliers. One way to cut the cost may be to tinker with the plants that biofuel is made from.
Take jatropha, for example. Lufthansa said last week that it had completed a series of more than 800 flights by an Airbus A321 that shuttled between Hamburg and Frankfurt while burning a 50 percent biofuel mix in one of its two engines. The biofuel was derived partly from jatropha, a tropical shrub with an oil-rich nut, and it cost about two and a half times what ordinary petroleum-based fuel does.
On Monday, the United States secretary of agriculture, Thomas Vilsack, speaking at Boeing’s headquarters in Chicago, identified a major impediment to the biofuels endeavor: the cost of harvesting and delivering the feedstock for biorefineries, the factories that make fuel from plant material.
Biologists and financiers are focusing on the problem. On Tuesday, a San Diego company, SG Biofuels, plans to announce $17 million in new financing from venture capital sources to continue its work on raising the yields from jatropha.
The company is trying to do for jatropha, whose fruit is inedible, what agronomists have done for food crops like wheat and corn, swapping genes among strains to produce varieties that are hardy and higher-yielding. The company said it had already raised yields of jatropha oil to 250 to 350 gallons per acre, double the normal output.
“Mother nature gave us a good foundation,’’ said Kirk Haney, the company’s chief executive. “But there is a lot of opportunity to push this plant to even higher yields.”
Jatropha is sometimes used to make hedges for containing cattle. Specialists say it was spread around the tropics by Portuguese sailors who believed it had medicinal properties. SG Biofuels has gone back to Central America, where the plant originated, to seek out more strains with favorable characteristics for genetic manipulation.
The plant produces a fruit the size of a golf ball with three black seeds, each about the size of an almond. The hulls of the seeds are burned for energy, and the seeds are then crushed to yield a triglyceride, an oil that can be converted at a refinery to diesel fuel or jet fuel.
Lufthansa used a mixture of jatropha and camelina, which is widely grown in the United States, and animal fats. After six months on the 50-50 blend, the engine appeared to be functioning normally, the airline said. The goal was to get an idea what the engine would look like after years of service on a lower blend.
(The fuel is blended because its energy content is slightly lower per unit volume than ordinary jet fuel is. It is somewhat comparable to the way that ethanol has a lower energy content than gasoline; if the energy content were allowed to get too low, cockpit instruments would have to be adjusted. But unlike ethanol, jet fuel from jatropha is a “drop-in” substitute, requiring no special distribution system or adjustments to the engines.)
Carbon dioxide emissions declined about 60 percent, gallon for gallon, with the biofuel, Lufthansa said, while noting the 2.5-times increase in cost.
Some airlines have reported an even higher differential.
Of the cost, 80 to 85 percent involves the feedstock, according to Lufthansa and Boeing, which worked with the airline on its test program. The project also included a flight by a Boeing 747 from Frankfurt to Washington last week, with the 50-50 blend loaded into the tanks feeding the two engines on the right wing.
Obviously, the cost has to come down: Lufthansa said it spent $8.4 million on the six-month test, with the European Union paying about one-third of the expense.
In a panel discussion in Chicago on Monday, Billy Glover, Boeing’s vice president for environment in its commercial airplane sector, said the company hoped to stabilize its greenhouse gas emissions by 2020 by using more efficient planes and more biofuels, while still allowing air travel to grow. By 2050, he said, the industry’s goal is to reduce emissions by 50 percent.
(In theory, the Obama administration’s goal is to cut American greenhouse gas emissions by 80 percent by that date, although the economy is not on track to accomplish that.)
Mr. Vilsack, the agriculture secretary, has been traveling the country preaching the virtues of fueling airplanes from farms. He said that his department would help establish eight to 10 biorefineries producing both vehicle fuel and aviation fuel.
The feedstocks will be specific to the region where the refineries were built — in some places, the nonfood parts of the corn plant, and in others, algae or switchgrass, he said. The department will subsidize the price of feedstocks to help bring the cost closer to competitive levels for the airlines, he said. The Navy has been lined up as a customer.
But, as with gasoline and diesel from nonfood biomass, the effort has not fully taken off. “We’re just now getting to point where we’re going to be producing this,’’ Mr. Vilsack said.