Laser-Induced Incandescence Measurements of Soot Production in Steady and Flickering Methane, Propane, and Ethylene Diffusion Flames.
Laser-Induced Incandescence Measurements of Soot
Production in Steady and Flickering Methane, Propane,
and Ethylene Diffusion Flames.
Shaddix, C. R.; Smyth, K. C.
Combustion and Flame, Vol. 107, No. 4, 418-452, 1996.
Sponsor:Gas Research Inst., Chicago, IL
soot; diffusion flames; methane; propane; ethylene;
atmospheric pressure; lasers; light scattering; flame
Quantitative experimental measurements of soot
concentrations and soot scattering are presented for a
series of steady and flickering coflowing methane,
propane, and ethylene flames burning at atmospheric
pressure. Flickering diffusion flames exhibit a wide
range of time-dependent, vortex-flame sheet
interactions, and thus they serve as an important
testing ground for assessing the applicability of
chemical models derived from steady flames. Acoustic
forcing of the fuel flow rate is used to phase lock the
periodic flame flicker close to the natural flame
flicker frequency caused by buoyancy-induced
instabilities. For conditions in which flame clip-off
occurs, the peak soot concentrations in the methane
flickering flames are 5.5 to 6 times larger than
flickering propane and ethylene flames is only 35 to
60%, independent of the flicker intensity. Soot
concentration profiles and full Mie analysis of the soot
volume fraction/scattering results reveal significant
differences in the structure of the soot fields and in
the roles of soot inception, growth, and oxidation for
the different hydrocarbon fuels. The soot
concentrations have been measured using laser-induced
incandescence (LII). Since this is the only technique
currently available for making time- and
spatially-resolved soot concentration measurements in
time-varying flow fields, considerable effort has been
devoted to developing LII for quantitative applications.
Important considerations include (1) proper calibration
measurements, (2) signal detection which minimizes
interferences from C2 Swan-band emission and broadband
molecular fluorescence, (3) correction for the laser
beam focus/spatial averaging effect in line image
measurements, and (4) correction for LII signal
extinction within the flame.