ACCESS II Confirms Jet Biofuel Burns Cleaner
NASA's DC-8 research aircraft leads one of the
ACCESS II sampler aircraft across the early morning California
sky.
Image Credit:
NASA / ORAU Richard Moore
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Flying high above the California desert, NASA researchers recently took to
the skies for the second year in a row with a DC-8 and other aircraft to study
the effects on emissions and contrail formation of burning alternative fuels in
jet engines.
This follow-up set of Alternative Fuel Effects on Contrails and Cruise
Emissions flight tests, known as ACCESS II, repeated a similar series of tests
flown during 2013, while also adding a few new wrinkles to the investigations to
capture more and better data. Within NASA, ACCESS II was a joint project
involving researchers at the Armstrong, Langley, and Glenn research centers. The
research supports NASA aeronautics' strategic vision, which has as a goal to
enable transition of industry to low-carbon fuels and alternative propulsion
systems.
“It went well,” said Bruce Anderson, NASA's principal investigator for
ACCESS. “We got beaucoup of data!”
A quick look at the ACCESS II data confirmed with high certainty the results
from ACCESS I, which showed at least a 50 percent reduction in soot emissions
from the DC-8 when it burns the blended fuel as opposed to the jet fuel alone,
Anderson said.
NASA's Matt Berry (left), a flight operations
engineer at NASA's Armstrong Flight Research Center, reviews the flight plan
with Principal Investigator Bruce Anderson.
Image Credit:
NASA / Tom Tschida
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It is hoped the research will help lead to more environmentally friendly
aircraft designs and worldwide flight operations, especially in light of the
explosive growth in global air travel that is forecast for the decades
ahead.
ACCESS II involved flying NASA's workhorse DC-8 as high as 40,000 feet while
its four CFM56 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.
Meanwhile, a trio of instrumented research aircraft took turns flying behind
the DC-8 at distances ranging from 300 feet to more than 20 miles in order to
take measurements on emissions and study contrail formation as the different
fuels were burned.
The trailing aircraft included NASA's HU-25C Guardian jet based at NASA's
Langley Research Center in Virginia, a Falcon 20-E5 jet owned by the German
Aerospace Center, and a CT-133 jet provided by the National Research Council of
Canada.
ACCESS II’s international flavor – a new plot element compared to ACCESS I in
2013 – definitely added value to the research and has already opened doors for
possible future collaborations for this type of scientific inquiry.
“We developed a very good working relationship,” Anderson said.
As part of the international team involved with this research, NASA will
share its findings with the 24 member nations that make up the International
Forum for Aviation Research, which NASA currently chairs.
ACCESS II mission timeline
Flight tests were staged from NASA's Armstrong Aircraft Operations Facility
in Palmdale, Calif., and mostly took place within restricted airspace high over
nearby Edwards Air Force Base.
They began May 7 with all four aircraft in the air to verify the test plan,
capture some in-flight photos and take a set of data from the DC-8 as it burned
only standard jet fuel. Three more flight sorties with all aircraft
participating followed on subsequent days, this time using the blended fuel.
The DC-8'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.
Image Credit:
NASA / SSAI Edward Winstead
Feature Link:
On May 12 a fifth data run was aborted when the two outboard engines of the
four-engine DC-8 flamed out. The DC-8 easily returned for a landing on its two
remaining engines, grounding the science gathering mission for 10 days while the
incident was investigated and the problem corrected.
It turned out the trouble was caused by a tiny pocket of air introduced into
the propulsion plumbing when a sample of fuel was taken on the ground before
takeoff. The air worked its way into a fuel pump that was feeding all four
engines, causing two of them to be starved for gas long enough to flame out.
“It had nothing to do with the blended fuel we were using, just the way the
system was configured in combination with the air in the line,” Anderson
said.
A change in procedures fixed the trouble and flight tests with the DC-8 and
the NASA research jet resumed on May 22, the German and Canadian aircraft having
departed for their home bases – but not before the NASA and German jets spent a
day chasing each other to study contrail formation.
Four more research flights took place testing the blended fuel through May
30, which was the last day of ACCESS II test operations.
Mission success
ACCESS II had two main goals:
- Measure and characterize the amount of soot and other pollutants generated
by burning jet fuel (with either high or low sulfur content) that was blended
with alternate biofuel.
- Gather basic data on contrail formation in the wake of a jet aircraft and
study how or if burning blended fuel altered the contrail formation in any
way.
Both goals were achieved to a much greater degree than ACCESS I in 2013,
although Anderson said weather conditions were not as cooperative for contrail
formation as often as the science team would have liked.
The view from inside NASA's HU-25C Guardian
sampling aircraft from very close behind the DC-8.
Image Credit:
NASA / SSAI Edward Winstead
Feature Link:
“We certainly could have used more contrail observations,” Anderson said.
“But we did make many more observations of contrails than we did before, and I
think we obtained the first data that will allow us to calculate how many ice
particles are formed per kilogram of fuel burned.”
The next step would be to correlate that data to the number of soot particles
coming out of the exhaust, which could help determine if the blended biofuel
would be a factor in reducing contrail formation. That analysis isn’t complete
yet, but Anderson is confident they have enough data to make a good stab at
answering that question.
In the meantime, it is more certain than ever that the blended biofuel is
cleaner to burn.
“Our findings show we definitely see a 50 percent reduction in soot emissions
from the DC-8 when it burns the blended fuel as opposed to the jet fuel alone,”
Anderson said, noting that while ACCESS I showed similar results, the quality of
data obtained during ACCESS II was far superior.
One reason for the improved data set was the result of extensive safety
reviews that came following ACCESS I, which led to allowing the NASA Guardian
jet greater flexibility in where it could fly behind the DC-8 to gather data
during ACCESS II.
An example of this was the option of flying through the DC-8’s wake vortices,
a turbulent swirl of air that airplanes – especially big ones – trail behind for
miles.
By flying through the DC-8’s wake the science instruments on the chase
aircraft were able to record more data about how the emissions mixed with air.
And even at a distance of 15 miles the experience was no walk in the park.
“It was something like a roller coaster at times as we were twisted one way
or another, that’s for sure,” Anderson said. “And yes, it was a good idea to
keep the airsickness bags handy.”
All of the aircraft, researchers and flight
operations people who made ACCESS II happen.
Image Credit:
NASA / Tom Tschida
Feature Link:
Ahead: Another ACCESS?
According to Anderson, for the moment they are concentrating on analyzing the
large amount of data collected from both the ACCESS I and II campaigns, so there
are no concrete plans yet for another NASA-led flight campaign. Instead, NASA
researchers and management continue to discuss potential future collaborative
efforts that could lead to further flight campaigns.
In the meantime, Anderson is hopeful his team will be able to conduct a
mission that will look more directly at how contrails grow and transition into
cirrus clouds, which are known to both trap and reflect different wavelengths of
energy – a variable in discussions about climate change.
“It’s generally believed that contrails warm the environment but there’s a
lot of questions regarding just how much heating and cooling are going on. But
our job is to make the best measurements of contrails and background conditions
possible and hand that data off to the climate modelers to chew on. In that
regard, I think we certainly fulfilled our responsibilities during ACCESS,”
Anderson said.
Jim Banke
NASA Aeronautics Research Mission
Directorate
NASA
Guillermo Gonzalo Sánchez Achutegui
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