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Soot in a Time-Varying Flame: Are Scattering and Extinction Measurements Sufficient?


pdf icon Soot in a Time-Varying Flame: Are Scattering and Extinction Measurements Sufficient? (428 K)
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.

Keywords:

combustion; soot; flame research; scattering coefficient; extinction; experiments; diffusion flames; flame flicker

Abstract:

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.