Effect of gas—phase carbon depletion by sooting on the structure of methane/air flamelets
The paper describes an approach to model soot formation/oxidation in nonpremixed turbulent flames, which in particular accounts for the effect of gas—phase carbon depletion due to sooting. The effect is relevant to combustion chambers fed with oxygen (rather than air), operating at high pressure and overall rich, such as rocket chambers. A scaled gas—phase elemental carbon mass fraction is introduced to this end and, in the framework of a laminar flamelet approach, a library is developed for use in turbulent combustion models. Due to the lack of reference data for rocket chambers conditions, the library is limited for the time being to nonpremixed methane/air flames at two values of pressure, 1 atm and 3 atm, for which experimental data are available. Results indicate a significant effect of carbon depletion on the concentration of soot precursor acetylene in particular, and on the ensuing soot nucleation rate. The model is shown to correctly capture the decrease of the latter rate with gas—phase carbon depletion, thereby potentially enabling to extend the range of applicability of semi—empirical soot prediction models for nonpremixed turbulent combustion.
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