Rising oil costs, energy independence from other countries and pollution are all major factors in the search for alternative sources of fuel. So it’s no surprise that U.S. government organizations are busily testing and searching for a viable non-petroleum-based jet fuel.

NASA’s Dryden Flight Research Center in California is testing two synthetic jet fuels drived from coal and natural gas. That move is in stark contrast to the Air Force, which just shelved a planned coal-to-liquids plant in Montana that would have used ore to create jet fuel.

RenTech, Inc. has conversely developed RenJet fuels from a variety of biomass and fossil fuesl via the Fischer-Tropsch process, which is a chemical reaction in which a mixture of carbon monoxide and hydrogen is converted into liquid hydrocarbons, resulting in synthetic petroleum.

The scientists are testing the emissions compared to that of standard jet fuel. Although they’re not sure what exactly comes out of the tailpipe, they speculate that synthetic fuels create fewer particles and other harmful emissions than standard jet fuel. An article in Fly Green! Magazine touts that Fischer-Tropsch fuel burns cleaner than traditional jet fuel, spitting out up to 90 percent less of the particulate pollution that muddies the air and causes health problems. If true, it could drastically improve air quality around airports, and perhaps decrease emissions created from flying.

"We’re still very much in the early research stage," said AAFEX project manager Dan Bulzan of NASA's Glenn Research Center in Cleveland. "[But] we know in the future these fuels are going to become important to aviation. Petroleum is dwindling and you're going to need to make fuel out of coal, natural gas and biomass."

The Defense Advanced Research Projects Agency (DARPA), part of the Department of Defense, is also testing an alternative to petroleum – algae. DARPA gave $35 million to San Diego-based companies SAIC and General Atomics to pursue the creation of algae-based jet fuel that would meet the goal of costing about $3 a gallon. Algae can produce as much as 100 times more energy per acre than crop-based biofuels.

Coal and natural gas are far from perfect answers, considering that they are not renewable sources of energy. Similarly, biomass has proven controversial because of the large amount of land and water needed, and associated environmental concerns, such as water pollution from fertilizers and pesticides, and soil erosion from runoff. A recently published paper shows converting many crops into energy requires more energy for the process than the crop actually produces as fuel.

So what is the best feedstock for jet fuel? Whatever the answer (perhaps algae?), there will most likely be some compromises, but it’s important that we don’t ignite a food and water crisis in the search for emitting less particles and pollution. There’s no point in replacing one huge problem with another.