Green jet fuels

Airline companies are experimenting with a variety of feedstocks, such as algae and jatropha, as green fuel. Till date, the best fuel for jet engines is kerosene, which comes from petroleum which emits a lot of carbon. A 5,000 mile flight emits a ton and a half of carbon dioxide for every person on the plane.

Why should I be aware of this?

Concerns about dependence on overseas oil for fuel and the possibility that jet-fuel prices could again spike as they did in 2008, have prompted a spate of test flights powered by bio-fuels made from the energy-rich extracts of flowering plants, weeds and pond scum.

All about green jet fuels

To be feasible, alternative jet fuel sources need to be compatible with petroleum and produce similar combustion performance. Test flights using various bio-jet fuels are showing consistently high-quality results.

In January this year, Japan Airlines flew a Boeing 747 for 90 minutes using a fuel made primarily from camelina — a flowering stalk that grows several feet tall — and small amounts of other plant oils. In the same month Continental Airlines conducted the first U.S. commercial jet flight. A Boeing 737 completed a two-hour test flight from Houston with one of its two engines running on a 50–50 blend of regular Jet A and a synthetic made from jatropha and algae.

Efforts to grow jatropha

In the meantime, efforts to grow jatropha — which is largely planted in Africa and India — may be scaled up while camelina is improved as a rotation crop with wheat. In order to make it viable, Jet fuel from camelina and jatropha should be at the correct price point—$80 per barrel or less—within three to five years and fuel from algae in eight to 10 years.

However, sourcing will continue to remain a problem. Critics question whether enough land would be available to meet demand. According to industry estimates, supplying 240 million gallons of jatropha fuel — which is roughly what would be required for Jet A — would need planting an area twice the size of France. It is also feared that jatropha yields are unreliable and that harvesting seeds from the inedible fruit is labor-intensive. Genetic advances in bio-fuel plants could make them more productive.

Microbial-derived jet fuel

A California startup says it has produced the world's first microbial-derived jet fuel, and independent tests show it behaves just like the stuff refined from oil.

The company, Solazyme, says that analysis of its algal jet fuel showed it didn't freeze at high altitude -- a common problem with biofuels -- and it had the same density, stability and flashpoint of conventional jet fuel. In all, the algal fuel met 11 of the most challenging standards, known as D1655, for aviation fuels set by the ASTM . That's a significant step toward commercial viability of an alternative fuel that can meet the rigorous demands of the aviation industry.

Bio-jet fuels from soybeans

Several companies are experimenting with bio-jet fuels derived from soybeans and other feed stocks, but Solazyme makes fuel by growing algae in fermentation tanks without sunlight, satisfying the eukaryotic organism's sweet tooth by feeding it a steady diet of sugar. The process has already led to algal fuel for cars, called Soladiesel, that works like conventional diesel fuel. Solazyme hopes to begin mass-producing it at a competitive price within three years. That could be optimistic, but Chevron is sufficiently impressed to join Solazyme in the endeavor.

Geographic sources of fuel

The composition of fuels changes with the geographic source, the refining process and even with the season," Dryer noted. "Since we have an energy security problem, we need to be sure that alternative fuel sources are going to work and, in order to do that, we need to understand exactly how petroleum-based fuels work alone and in combination with alternative fuels."

Alternative energy sources, if designed appropriately, also could significantly reduce the amount of greenhouse gasses released in creating and burning jet fuel. According to the U.S. Department of Transportation, aviation is responsible for around 10 percent of the greenhouse gas emissions from transportation in the nation, or roughly 2.7 percent of the country's total greenhouse gas emissions

Can farms keep up with the demand?

The real question will be whether farms could keep up with the demand for biofuel feedstock along with the increased food needs of a world heading towards 9 billion people, especially if biofuels take on a leading role as a green car fuel, too. Even assuming that the aviation biofuel can be made from non-nutritive biomass (stalks, leaves and such), and various bio-hacks can make the plants grow faster, it's unlikely that we'll be able to cover all three industries. More likely is that automotive biofuels are transitional, while aviation will rely on biofuels for decades to come.

90 degrees

The bigger question is whether the current air travel paradigm will continue. High fuel prices aren't the only threat: shaky financial performance, fickle consumers, and the rising threat of pandemic could each send the air travel industry crashing. Conversely, alternative models of air travel, including next-generation airships, could make flight cleaner and more like a cruiseship than a sardine can.

References:

• Future Solutions: GreenJet Fuels
• Green skies: Engineer's work may reduce jet travel's role in global warming
• Fly Green
• Algal Jet Fuel One Big Step Closer to Reality