Effect of alternative fuels on aircraft emissions: Fuel strategy and characterization

The ECLIF (Emission and CLimate Impact of alternative Fuels) project aimed at linking fuel composition and properties to aircraft engine emissions and then further to contrail cirrus properties, and to climate. Two aspects in the methodology were essential. On the one hand the implementation of a fuels matrix, which ensured relevance with respect to existing and future alternative aviation fuels. The fuels under study differed in their production technology (fossil conventional, fossil alternative, or sustainable alternative jet fuel) thus in their composition and properties. On the other hand, there were lab-scale experiments and modeling prior to and after the two field campaigns, which aimed at linking engine emissions measurements (ground and flight) with fundamental combustion processes. Both campaigns were carried out in Germany and had the DLR A320 Advanced Technology Research Aircraft (ATRA) equipped with IAE V2527-A5 engines as the source aircraft burning different ASTM D1655 certified Jet A-1 fuels. During ECLIF-I (2015) the DLR Falcon CMET was the chaser probing the plumes and during ECLIF-II/ND-MAX (2018) it was NASA's DC-8, the flying lab.

In ECLIF, soot is the common denominator between the laboratory and the aircraft experiments. The systematic investigation started with chemical analytics, which provided the necessary information regarding each fuel's chemical composition (using GCxGC) and selected physical properties (e.g. mass density, viscosity, net heat of combustion, distillation curve…). Then, fundamental aspects of fuel oxidation (combustion) were investigated in a hot atmospheric pressure flow reactor equipped with a molecular beam mass spectrometer. Intermediate species profiles were measured under controlled conditions and in particular soot precursors. High-pressure spray combustion rig test were also performed and provided information regarding soot concentration in the stabilized flame of an aircraft engine-relevant combustor. Here we report on the fuel strategy, on the characterization and properties of all fuels used during ECLIF-I and ECLIF-II/ND-MAX, and on selected laboratory experiments.