NASA and the German Aerospace Center are partnering on joint research flights in Germany for the first time, with a project investigating emissions from biofuels and ice crystals in condensation trails.
The research flights are intended to determine particle emissions and how they affect cloud formation through condensation trails (contrails), and to investigate their impact on the climate.
NASA’s DC-8 research aircraft is visiting Germany this month (January 2018) and flying with the DLR A320 Advanced Technology Research Aircraft (ATRA). The research flights will start from Ramstein Air Base.
Bruce Anderson, NASA’s principal investigator for the research, said, “NASA could not do this alone. We’re bringing the two agencies together to combine resources and facilities to study alternative fuels in an unprecedented way.”
Fuel blends
The ND-MAX/ECLIF 2 (NASA/DLR-Multidisciplinary Airborne eXperiments/Emission and CLimate Impact of alternative Fuel) flight campaign will test various fuel blends on DLR’s A320. NASA’s fully instrumented DC-8 will follow at a distance, measuring soot particles, gas emissions and ice crystals in ATRA’s exhaust gas stream.
Hans Schlager from the DLR Institute of Atmospheric Physics said, “We have installed instruments on board the DC8 to simultaneously measure the size distribution of soot and ice particles and gas emissions as it follows in the wake of ATRA.”
“The focus of our measurements is to characterize the emissions produced using different fuel blends. We are particularly interested in finding out how the soot emissions of the different fuels affect the radiation properties and lifetime of the contrails.”
The HEFA biofuel selected for these trials is largely derived from the oil of Camelina plants, representative of alternative fuels, which could also be synthetic.
André Krajewski from the DLR Flight Experiments facility said, “We have created fuel blends that contain 30% to 50% hydroprocessed esters and fatty acids (HEFA), which will be used in a total of eight planned joint-research flights.”
In addition to the emissions, the international research team will look at how the different fuel blends affect the performance of the engines.
“Biofuels such as HEFA differ in their composition from conventional kerosene in that they are pure paraffins and contain no cyclic hydrocarbons. When mixed with conventional jet A-1 kerosene, one obtains an approved fuel,” said Patrick Le Clercq of the DLR Institute of Combustion Technology. “The modified fuel composition has an impact on the formation of soot during combustion.”
Previous joint-research flights
In recent years, several research campaigns into alternative fuels have been conducted in the USA and Germany under different meteorological conditions. Earlier NASA-led research campaigns, called ACCESS I and II (Alternative Fuel Effects on Contrails and Cruise Emissions), were carried out in California in 2013 and 2014.
During these campaigns, NASA’s DC-8 flew with alternative fuels, while smaller research jets such as the NASA HU-25 Falcon and the DLR Falcon 20 conducted measurements in its exhaust stream. The ECLIF campaign followed in 2015 and was led by DLR in Germany, with the involvement of a number of NASA researchers. In this campaign, the DLR A320 ATRA flew with alternative fuels, while the DLR Falcon 20, equipped with instruments, followed behind, carrying out measurements of the emissions and contrails. In addition, extensive emissions readings were carried out from the ground.
Previous results from research flights have shown a significant reduction in soot particles when alternative fuels are used and suggest that this also leads to a lower quantity of ice crystals in contrails.
“Lower soot emissions from these alternative fuels are good news for the environment, and it would be even better if the flight tests confirm that using alternative fuels also reduces the number of ice crystals in contrails,” said NASA’s Bruce Anderson.
“This is a significant issue because contrails and the cirrus clouds that are formed as a result are thought to have a greater warming effect on Earth’s atmosphere than the total carbon dioxide emissions that have accumulated as a result of air travel over the last century or more,” added DLR researcher Hans Schlager.
Contrails contain many small ice particles that form due to the condensation of water vapor on the soot particles in aircraft exhaust gases. Contrails can linger for several hours in humid, cold conditions at altitudes of between 8km and 12km, forming high-level clouds called contrail cirrus.
Depending on the position of the sun and the ground, these clouds can have a local warming or cooling effect. Knowledge of this is essential for assessing the climate impact of aviation. The research conducted thus far suggests that a warming effect is predominant globally.
The flight tests are being conducted in Germany because the weather conditions in Germany favor the planned measurement of ice crystals.
If everything runs smoothly with the final preparations for the joint-research flight campaign, the first joint flight test will take place on January 16, 2018. A total of 80 flight hours for taking measurements are planned between then and February 2.
