Aviation biofuel pollutant emissions and contrails investigated

A joint project between the German Aerospace Center (DLR) and NASA is aiming to determine whether aircraft pollutant emissions are reduced by using biofuels. In addition, the pioneering new study aims to determine the effects alternative aviation fuels have on the formation of contrails.

With additional participation from the Max Planck Institute for Chemistry and the Institute for Atmospheric Physics of the Johannes Gutenberg University (JGU), the scientists performed eight test flights at varying altitudes to compare traditional aviation fuels against biofuels.

In each test, DLR’s Airbus A320 was fuelled with a different blend of kerosene and oil of Camelina based biofuel. NASA’s “flying laboratory”, a DC-8, followed a few kilometres behind, flying in the Airbus’ exhaust plume. Among the instruments on the flying laboratory were the ERc Instrument for Chemical composition of Aerosols (ERICA), from the Max Planck Institute and JGU Mainz.

“ERICA is a globally unique aerosol particle mass spectrometer, developed and built in Mainz,” explained MPIC Director Stephan Borrmann, a professor at the Institute for Atmospheric Physics at JGU.

NASA and DLR have been researching whether aviation biofuels are more ‘eco-friendly’ for some time. According to a statement from the University of Mainz, previous studies have shown that 50% and 70% less soot particles form from a 50% biofuel mixture with 50% normal kerosene.

"We are interested in the chemical composition of the exhaust particles, among other things, because we want to know how many soot particles the exhaust gas contains, how many metal-containing particles, if they are coated with condensable materials, and how the particles change in contrail formation," says postdoctoral researcher Sergej Molleker from the Particle Chemistry Department of the MPI for Chemistry.

“At altitudes of eight kilometres, soot particles and water vapour form ice crystals at -50C, which can be seen in the sky as contrails. Among other things, the ice crystals prevent heat from escaping the atmosphere into space, meaning that every contrail creates its own small greenhouse effect.”

"If we find a way to reduce the soot particles in the aircraft exhaust, the climate-warming effect could be reduced by new fuel blends," says Stephan Borrmann. "We also have the opportunity to make rare and valuable measurements of the natural ice clouds (cirrus) at this altitude, the properties and effects of which are also a key research topic."

According to a statement, initial results are expected from the test flights within two months.

Keep reading: Qantas completes first trans-Pacific biofuels flight