Soot in a Time-Varying Flame: Are Scattering and Extinction Measurements Sufficient?
Soot in a Time-Varying Flame: Are Scattering and
Extinction Measurements Sufficient?
Harrington, J. E.; Shaddix, C. R.; Smyth, K. C.
Combustion Institute/Eastern States Section. Chemical
and Physical Processes in Combustion. Technical
Meeting, 1993. October 25-27, 1993, Princeton, NJ,
390-393 pp, 1993.
combustion; soot; flame research; scattering
coefficient; extinction; experiments; diffusion flames;
Laser-sheet scattering images of the soot region in a
time-varying methane/air diffusion flame, whose fuel
flow is modulated at a frequency matching the 10.13 Hz
laser repetition rate, show at least a factor of ten
enhancement in volume integrated scattering intensity
when compared with images of a steady-state flame with
the same mean fuel and air co-flows. However, only a
small enhancement (~50%) appears in a comparison between
the peak values of what is commonly interpreted as soot
volume fraction, obtained through tomographic
reconstruction of HeNe and Ar ion extinction
measurements. The time-averaged soot, volume fraction
in the entire flame is identical, within our measurement
error, for the steady and time-varying flames. We
anticipate an explanation of our scattering and
extinction results based on changes in particle size and
morphology induced by a different time-temperature
history in the flickering flame.