Convective mass transport as the rate-determining step in pool flames and its analogy to the combustion of pollutants in the atmosphere.
In: Berichte der Bunsen-Gesellschaft, Jg. 82 (1978) ; Nr. 11, S. 1202-1217
Zeitschriftenaufsatz / Fach: Chemie
Mass transport in n-hexane [110-54-3] and n-butane [106-97-8] pool flames was detd. from concn. distribution of soot, fuel, O, and CO2 under consideration of the flame shapes obtained from time exposures. Combustion in pool flames proceeds predominantly in a thin, conical zone of the flame neck and the effective transport into this zone is the rate-detg. step. The soot concn. is calcd. by means of an empirical pyrolysis equation. The main part of the n-butane is transported within the flame neck and has an effective diffusion coeff. which is .apprx.10 times greater than the mol. diffusion coeff. In the turbulent region beyond the flame neck (flame plume), concns. of the n-butane ad n-hexane were <0.05 vol.%. A turbulent mass transport of soot, CO2, and O occurs there whose concn. distributions may be calcd. by use of a statistical Gaussian distribution model. For each pool flame space-dependent, turbulent exchange coeffs. were calcd. which for the n-butane pool flame, are .apprx.5 times greater than the effective diffusion coeff. in the flame neck. The dispersion parameter governing the turbulent mass transport of the 3 substances is similar and has the magnitude as the distribution parameters of air pollutants in the atm. Finally, the space-dependent mass exchange coeffs. were explained by tha dimensions of the eddies which have the same length scale as the instantaneous flame widths.
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