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Jet contrails
During flight tests led by NASA, a DC-8 research jet’s four engines burned either JP-8 jet fuel or a 50-50 blend of JP-8 and renewable alternative fuel of hydro processed esters and fatty acids produced from camelina plant oil. (NASA / SSAI Photo / Edward Winstead)

A NASA-led study demonstrates that airplanes powered by biofuels can emit up to 70 percent less particulate pollution – providing a potential boost for technologies that are being pioneered at Seattle-Tacoma International Airport.

The study, published today by the journal Nature, was conducted in the skies over NASA’s Armstrong Flight Research Center in California. But the findings could be applied at Sea-Tac, where the Port of Seattle, Alaska Airlines and Boeing are partnering to work toward having biofuel available for every flight.

NASA’s flight tests in 2013 and 2014 were part of a series of experiments known as the Alternative Fuel Effects on Contrails and Cruise Emissions Study, or ACCESS.

Researchers wanted to find out whether biofuels had an effect on the formation of contrails, the cloudy trails that are produced when the hot exhaust of a jet engine mixes with cold air at high altitudes. Persistent contrails can evolve into long-lived clouds that wouldn’t form otherwise, affecting atmospheric conditions.

During the flight tests, NASA flew its DC-8 research jet to altitudes as high as 40,000 feet. The biofuel was a 50-50 blend of traditional Jet A aviation fuel and an alternative fuel produced from camelina plant oil. Three other aircraft took turns flying behind the four-engine DC-8, at distances ranging from 300 feet to more than 20 miles away, to measure the emissions and study contrail formation.

“This was the first time we have quantified the amount of soot particles emitted by jet engines while burning a 50-50 blend of biofuel in flight,” Rich Moore, lead author of the Nature report, said in a NASA news release. Previous tests have been done with engines on the ground.

The study determined that particle emissions were reduced by 50 to 70 percent at cruise conditions, compared with the emissions from straight Jet A fuel. The reduction was less pronounced at high-thrust settings than at low to medium thrust.

Bruce Anderson, ACCESS project scientist at NASA’s Langley Research Center, said soot emissions are a major determining factor for the formation of contrails and their properties.

“As a result, the observed particle reductions we’ve measured during ACCESS should directly translate into reduced ice crystal concentrations in contrails, which in turn should help minimize their impact on Earth’s environment,” Anderson said.

In their Nature paper, the researchers noted that it’s complicated to gauge the total effect on contrails: Although the ice crystal concentrations should be reduced, the frequency and ice mass of contrails may actually increase due to the higher hydrogen content in the biofuel blend.

Further experiments will be conducted to tease out those effects.

Moore and Anderson are among 27 authors of the Nature study, “Biofuel Blending Reduces Particle Emissions From Aircraft Engines at Cruise Conditions.” The work was supported by research programs at NASA, the German Aerospace Center (DLR), Transport Canada and the National Research Council Canada.

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