The Other Reasons the US Military Loves Biofuels

Jet Fighter

By:  Tom Schenk, Director of US Business Development, TerViva

To an outsider, hearing that the Department of Defense is interested in biofuels, it would be easy to conclude that the military’s interest rests mainly on concerns on the security of our energy supplies in wartime from not-so-friendly foreign countries.  While this is partially true, there is quite a bit more to the story than supply chain concerns or sustainability initiatives from a department of government that consumes about 8 billion gallons of fuel annually.

Fuel has occupied a critical part in modern military history. For example, in World War II, the German Luftwaffe ran their fighters on 87 octane fuel.  The British were at a continuous disadvantage with their slower Spitfire fighter aircraft until the US introduced 100 octane fuel plus a propeller modification.  This gave the British about a 30mph boost over the German fighters which allowed them to fly higher and faster in a dogfight and out-maneuver the German fighters.

Weight                                                                                                                                                                             In 2012, tests at the Air Force Research Laboratory at Wright Patterson Air Force Base near Dayton, Ohio came up with two compelling reasons for the US military to have an interest in biofuels. Special advisor to the Air Force on energy and fuels, Omar Mendoza, stated that one of the initial findings was that bio-based jet fuels have about 7% less mass than conventional jet fuel.  This lowered the weight of the airplane making it possible for jets to fly faster and farther as well as carry more of a payload – cargo or weapons systems. 

Bio jet fuels have about 4% more energy per mass than fossil-based jet fuel.  A 2012 Biofuels Digest article discussing this topic noted that for an F-18 taking off with a full load of armaments and the tanked topped off, the difference in the two fuels could be close to 1000kg. That warplane could carry an extra missile for that weight difference. With the superior energy/mass ratio, it could also fly farther, too.

Temperature                                                                                                                                                                                 The second major finding from the tests was that bio-based jet fuels can burn significantly cooler. Terry Yonkers, assistant secretary for installations, environment and logistics, stated that initial studies by the Air Force have shown that temperatures in the engine combustion chamber can be as much as 135 degrees Fahrenheit lower when biofuels are used instead of conventional (fossil-based) jet fuel. Fossil-based jet fuel contains numerous impurities whish do not completely combust in the engine.  This leads to soot deposits which cause high temperatures to radiate throughout the engine. Long periods of high temperatures can cause any metal to fatigue and fail.

In 2012 at a roundtable meeting in Washington DC jointly organized by the USDA and the DoE, Mendoza pointed out that, “At the temperatures that military jet engine perform at, an additional 25 degrees in temperature can shorten the life of the engine by half. Military showed data showed that engine parts could last up to 10 times longer, if the new high performance fuels were employed in place of conventional fossil fuels.” Mendoza pointed out that a roughly 10C drop in wall temperature results in doubling of the life of the hot section of a jet engine.

The weight and temperature components of biojet fuels mean economic savings in addition to its green footprint.  These facts have not been lost on commercial airline carriers.  KLM, Alaska, and United, just to state a few, have had many flights tests on biojet fuels.  The greatest challenge is producing the feedstocks for the refining of these fuels in sufficient quantities to transform these studies into a commercially viable reality.

At TerViva, our work in scaling pongamia oilseed tree plantations is making significant headway in this effort.  Because pongamia oil is a long-chain (C 18:1) carbon, it makes it an ideal non-food sourced feedstock for refining into jet fuel, diesel, as well as numerous biochemical compounds for industry.

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