ECLIF/ND-MAX - Impact of alternative jet fuels on particle emissions and contrail formation of aircraft in cruise

We present preliminary results from the ECLIF/ND-MAX flight campaign, which investigated the efficacy of using alternative fuels and clean-burning jet engines to mitigate the growing climate impacts of aviation. Sponsored by DLR and NASA the project used the NASA DC-8 research aircraft, equipped with a variety of trace gas, aerosol and ice particle instruments to characterize emissions and contrails produced by the DLR A320 Advanced Technology Research Aircraft (ATRA) in cruise as it burned different mixtures of HEFA (hydro-processed esters and fatty acids) fuel with conventional Jet A-1 fuel. Cloud and aerosol properties and trace gas concentrations were measured as the DC-8 crossed the ATRA plume hundreds of times over a range of altitudes, engine states and meteorological conditions during seven formation flights conducted over northern Germany in winter 2018. Data were also recorded within contrails from other aircraft encountered during transits to and from the experiment area and during a DC-8 flight dedicated to sampling emissions from A320-class commercial aircraft equipped with a new generation of low-emission, lean-burn engines. Our analyses are focused on establishing the effects of fuel and engine technology upon gas-turbine soot emissions and, in turn, how the soot concentrations along with ambient conditions regulate number density and microphysical properties of contrail ice particles. Initial results indicate that the ATRA soot emissions were roughly proportional to fuel aromatic-hydrocarbon content. The low sulfur-content blended fuels also suppressed formation of the nucleation-mode sulfate aerosols that are generally associated with burning Jet A-1 fuels. Lean-burn engines produced significantly lower soot emissions than the ATRA's IAE2527 engines; the effects of these reductions on contrail characteristics are investigated.