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The Case Of The Vegetarian Jet Engine

By Ideas Lab Staff July 27, 2012

How GE jet engines running on vegetable oil mix broke the sound barrier.

Generations of farmers have looked at the humble Camelina plant and saw weed. Mike Epstein, who leads alternative fuels development at GE Aviation, sees jet fuel. “It’s an amazing story,” Epstein says. “You just have to chemically modify it a little bit. Once you’ve done that, you’ve got something that looks very close to kerosene.”

Thanks to Epstein and his team, GE jet engines now burn biofuel blends from plants like Jatropha, a toxic desert shrub, wood chips, and algae. A GE-powered Embraer jet will take off for a test flight during Rio+20, the U.N. sustainable development conference held in Brazil this month. “We chip at the problem a bit at a time,” Epstein says.

Taking a fuel sample.

The chemistry that converts biomass to jet fuel has been around for many decades. But the chemical industry used the process mainly to manufacture soap and other goods based on fatty acids from plants, because jet fuel made from petroleum was cheaper. The math changed when the price of a gallon of oil crossed $100 in 2008. “That took the art of the possible to the art of the practical,” Epstein says.

To be clear, GE makes jet engines, not jet fuel. But the company helps customers like airlines, aircraft manufacturers, and the military to switch to biofuels without any hiccups. “We look at these fuels to make sure that our fuel nozzles and our entire fuel system works as advertised,” Epstein says. “Our customers don’t need to modify anything. That’s the goal.”

Epstein has been building GE jet engines for more than two decades, including combustion systems and fuel research. He says that aviation has been stuck with kerosene because of its chemical properties. It packs the right amount of energy per gallon and weight, and any replacement has to match that. “We won’t be flying on batteries, fuel cells or nuclear reactors any time soon,” Epstein says.

Another hurdle is airport infrastructure. “Aircraft, engines, airport fuel hydrants, even interstate pipelines have been designed and built around jet fuel,” Epstein says. “Switching to fuels that are chemically and physically different from [kerosene] would cost trillions.”

Esptein and his team analyzed and rejected obvious biofuel choices like ethanol. “Design engineers have looked at these choices and the results were not pretty,” he says. “Ethanol has much lower energy density than conventional jet fuel. You’d have to carry a lot of it around.”

But in 2008, the team scored a hit when a Virgin Atlantic jumbo jet powered by four GE CF6 engines burning biodiesel flew from London to Amsterdam. “The energy density was still not good, but it was a fantastic first step,” Epstein says. “There were a lot of critics who said that we’d never fly with biofuel and this flight demonstrated that we could. It evolved from here.”

Just two years later, on Earth Day 2010, a NAVY F/A-18 fighter jet dubbed “Green Hornet” flew at 1.7 times the speed of sound with tanks filled with a half-and-half mix of Camelina fuel and kerosene. The Green Hornet was powered by two F414 GE engines manufactured by workers in Lynn, Massachusetts.

Today, BoeingAirbus, Embraer and many airlines have flown biofuel tests. Price remains a sticking point but the fuel could dramatically improve their greenhouse gas footprint. Innovative refinery companies are also jumping in to bring fuel costs down. “We’ve started the transition,” Epstein says. “We’ve taken the first steps.”