AAFEX-II and the search for alternative aviation fuel: interview with NASA’s Bruce Anderson, World Petroleum Council Guide: Biofuels, 2016

AAFEX-II and the search for alternative aviation fuel: interview with NASA’s Bruce Anderson, World Petroleum Council Guide: Biofuels, 2016


NASA’s Bruce Anderson discusses his biofuels research and how animal tallow and camelina oil could help reduce global warming

[I worked at International Systems & Communications (ISC) from 2015-17, a small publisher in Pimlico who put together educational guides for the World Petroleum Council. I put my heart and soul into its Biofuels edition – commissioning some of the world’s experts in this field to write a few words for no payment. All the images were either my own, supplied by companies or from a free-to-use photo site. The owner of ISC is a great fellow called Robert Miskin – a Factory Records nut. I managed to get this interview with one of NASA’s biofuels scientists who’d been experimenting with jet engines.]

World Petroleum Council Guide: Biofuels, 2016

In 2011, an article by Ulrike Burkhardt and Bernd Kärcher at DLR, Germany’s aeronautics and space research centre, revealed that aviation contrails – the lines of cirrus cloud created by aircraft – were the largest constituent of aviation-induced global warming. Studying 2002’s air-traffic inventory, the report went on to state that our current climate is more affected by contrail-induced cloudiness than by all the carbon dioxide emitted by every aircraft that has ever flown.

Prior to the paper’s release, NASA had tested non-petroleum jet fuel as part of its Alternative Aviation Fuel Experiment (AAFEX). AAFEX had two primary tasks: reducing dependence on foreign oil and finding less-polluting aviation fuel, but as the experiment unfolded, it became clear that actual testing on contrails was needed. AAFEX-II, with NASA partnering DLR, took place above California in 2011. Although it was a bumpy ride, emissions readings were taken from engines powered by exotic biofuel blends. We speak to Bruce Anderson, AAFEX-II’s lead scientist, about his findings.

WPC: Should we be giving more thought to alternative aviation fuel?
Bruce Anderson: Regular jet fuel creates CO2 and other pollutants and it has double the aromatic hydrocarbon content of biofuel, leading to soot formation, which is also bad for air quality. Alternative fuels burn cleaner and can be produced from renewable feedstocks. Some of the fuel we used in the AAFEX-II experiments was made from animal fat – chicken and beef tallow and we also tested fuel made from camelina oil [a plant oil]. These fuels create less CO2 and less greenhouse gases.

Why are contrails bad?
Contrails probably contribute more to atmospheric warming than CO2 from aviation. Some say that contrails are 3-5% of the total radiative forcing and it’s particularly noticeable where there’s a lot of aircraft traffic, like here on the US east coast. We get contrails that completely paint the sky.

When testing, you flew behind NASA’s DC-8 aircraft. Isn’t there a turbulence hazard flying behind an aircraft?
There was concern that when we were chasing a DC-8 with a small aircraft, we would get caught up in wake turbulence, which would damage our aircraft or cause us to have an engine flame out. One of our rules was that we had to be within gliding distance of an airport. And then we couldn’t enter the exhaust wake of the DC-8 further back than 300 metres. From 300 metres to 14 nautical miles behind the DC-8, we weren’t supposed to fly in the contrails because the turbulence would be so intense.

Did you go into the wake?
Yes. A typical flight plan was to rendezvous with the DC-8, then alternately move the top of our aircraft into the exhaust of the left and right port engines. We had instruments on top of our aircraft where we drew in exhaust samples and measured the soot quantity. We also had an ice-particle probe that counted the number and measured the size of ice particles. There’s a lot of turbulence shed at the tips of aircraft wings, so-called ‘wing vortices’. You’ll have seen four-engine aircraft fly overhead. Initially, there’ll be four contrails but 500 metres behind the plane, there’ll be two. What happens is, the exhaust from the engines is caught up in the wingtip vortices, which are little horizontal tornadoes. They can cause catastrophic failure to planes.

What was your experience in the wake?
In the States, we have lots of gravel roads. It’s like riding over washboard gravel – with those ripples in the road, real bumpy. In the experiment, we had forward video camera and displays in front of the instrument operators’ seats. I was in the back of the plane, so I could watch the video and see where we were and had a good situational awareness. I didn’t get sick or feel bad. DLR, who were our partners in the experiment, had a similar aircraft but the people in the back of theirs didn’t have displays and didn’t know what was going on, so they just experienced periodic turbulence and wing roll out. There were people getting sick on their plane. It can be rough.

Did you find that fewer contrails were created when burning biofuels?
The blended fuel produced 40-60% fewer soot particles and less soot mass. There’s a significant reduction in soot when you burn cleaner fuel. But a large fraction of the water that condenses in the contrail is from the background atmosphere, not aircraft exhaust. With very cold days, when the atmosphere is dry, a contrail will form and quickly evaporate. Around this 50-mile racetrack over California that we were flying, there were variable amounts of water vapour, large fluctuations, so we didn’t have homogeneous conditions to see if exhaust soot was controlling the contrail density. It’s a tough experiment.

Are further experiments planned?
We’re hoping to repeat it with the Germans.

Is working for NASA as much fun as it sounds?
I’ve been here for 25 years and enjoy it very much. We have lots of world-class assets and aircraft that we can put instruments on. We have expensive, unique tools that we can access to take on important experiments. It’s a good environment to do science in. I’m within a few years of retirement but we’ve got some young people coming in to continue the work. They’re very hard working and I think we’re going to make progress. LG