Pb. Sunderland et al., SOOT FORMATION IN WEAKLY BUOYANT ACETYLENE-FUELED LAMINAR JET DIFFUSION FLAMES BURNING IN AIR, Combustion and flame, 100(1-2), 1995, pp. 310-322
The structure and soot properties of weakly buoyant, acetylene-fueled,
laminar jet diffusion flames were studied experimentally for combusti
on in air at pressures of 0.125-0.250 atm. Properties along the axis,
where soot processes are similar to behavior within nonbuoyant diffusi
on flames, were emphasized. The following measurements were made: soot
volume fractions using laser extinction, temperature using both therm
ocouples and multiline emission, soot structure using thermophoretic s
ampling and analysis by transmission electron microscopy, concentratio
ns of major gas species using sampling and analysis by gas chromatogra
phy, and velocities using laser velocimetry. As distance increased alo
ng the axis of the present acetylene-fueled flames, significant soot f
ormation began when temperatures exceeded roughly 1250 K, and ended wh
en fuel equivalence ratios decreased to roughly 1.7, where the concent
ration of acetylene became small. This behavior allowed observations o
f soot growth and nucleation for acetylene concentrations of 6 x 10(-6
)-1 x 10(-3) kg-mol/m(3) and temperature of 1000-2100 K. Over this ran
ge of conditions, soot growth rates were comparable to past observatio
ns of new soot in premixed flames, and after correction for effects of
soot oxidation yielded essentially first-order growth with respect to
acetylene concentrations with a negligible activation energy, and an
acetylene/soot collision efficiency of 0.53%. Present measurements of
soot nucleation rates also suggested first-order behavior with respect
to acetylene concentrations but with an activation energy of 32 kcal/
gmol and with rates that were significantly lower than earlier estimat
es in the literature. Nevertheless, uncertainties about effects of soo
t oxidation and age on soot growth, and about effects of surface area
estimates and translucent objects on soot nucleation, must be resolved
in order to adequately define soot formation processes in diffusion f
lames.