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

Abstract

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 graphenelike 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.

In-situ neutron imaging of hydrogenous fuels in combustion generated porous carbons under dynamic and steady state pressure conditions

“…This material showed considerable "thermal elasticity" with a density that changed by 30% between 300 and 600 K, approximately. We have also observed that flames can produce graphene/sheet-like structures either in few layers [10] or as components in the soot particles [11]. These structures are characterized by a high surface-to mass ratio, and in principle, the surface properties of the nanostructure subunits of soot particles can be changed by preparation utilizing controlled 4 (37) oxidation processes.…”

“…Graphitic structures with plane separation around 3.6 Å that are slightly smaller in value have been have been reported from both X-ray scattering and HRTEM on soot. Larger spaces can also be found for regions with more strand-like structures on the surface of less dense soot particles, which contain folded carbon or graphene structures with diameters that may exceed 10 Å [11]. Consequently, these may act as pockets or pores on the surface, which have a higher tendency to absorb methane at higher pressures.…”

“…Since X-ray attenuation is weaker for hydrogen than for carbon (for 10 keV radiation it as about 73 times), hydrogen detection can thus be three orders of magnitude more sensitive utilizing cold neutrons instead of hard X-rays. In practice, neutrons would be able to detect pressurized gaseous hydrogen surrounding carbon nanoparticles and thus be well-suited for the study of the interaction hydrogen and methane with carbon nanoparticle assemblies such as soot, the structure of which can be characterized by X-ray scattering techniques (see [5][6][7]9,11] and references therein).…”

“…The transmitted neutron beam flux, I, i.e., number of neutrons per area and time units can be expressed by the Lambert Beer law according to eq. (11). I0 is the flux of the incident beam on the cell, acell is the attenuation due to the cell material,  is the linear attenuation coefficient in cm -1 and D is the sample thickness and diameters in cm of the sample and reference cells.…”

“…Although hard X-rays have been used to characterize soot structure in flames (see e.g. [11] and references therein), it is relatively difficult to evidence the contribution from hydrogen, due to its low cross section. In addition, many of the electron microscopy techniques also have a problem with identifying hydrogen in samples.…”