Measurements of structures and concentrations of carbon particle species in premixed flames by the use of in-situ wide angle X-ray scattering

In-situ wide-angle X-ray scattering (WAXS) measurements have been conducted on atmospheric-pressure fuel-rich premixed freely propagating ethylene/oxygen flames with argon and nitrogen dilution. In this work, a novel analysis methodology able to provide quantitative information on soot/carbon particle species and concentrations was tested under heavy sooting conditions. The particle composition and concentrations were retrieved by fitting theoretical calculations of structural components from major molecular and nanometric species to the experimental WAXS data. The results show that argon dilution yields predominantly graphene-like components that are less stacked and amorphous carbon that is less structured than under nitrogen dilution. This finding was later confirmed by electron microscopy analysis on samples extracted from similar flames. In addition, the WAXS showed that most of the carbon present in the flames was bound as particles. These results constitute some of the first in-situ observations on structures and concentrations of carbon species in laboratory burner flames operating without stabilization plates.