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Asymptotic and Numerical Analysis of a Premixed Laminar Nitrogen Dioxide-Hydrogen Flame.


pdf icon Asymptotic and Numerical Analysis of a Premixed Laminar Nitrogen Dioxide-Hydrogen Flame. (1323 K)
Linteris, G. T.; Williams, F. A.

Combustion Science and Technology, Vol. 105, No. 4-6, 163-73, 1995.

Sponsor:

National Science Foundation, Washington, DC

Keywords:

premixed flames; laminar flames; nitrogen dioxide; hydrogen; burning rate; flame structure

Abstract:

A kinetic mechanism of eighty-some reactions for flames in mixtures of hydrogen and nitrogen dioxide is systematically reduced to twenty-four-, eleven-, seven-, two-, and one-step mechanisms. The numerically predicted burning rates for the full mechanism are compared with the results using the reduced mechanisms, and the sources of inaccuracies are identified. The two reactions NO2 + H -> NO + OH and H2 + OH <- -> H2O + H account for about 97% of the NO2 and H2 consumption and NO and H2O production and are the principal reactions involving OH and H atoms. The reactions 2 OH <- -> H2O + O and NO2 + O -> NO + O2 are important for OH and O, while the reactions NO2 + M -> NO + O + M and NO2 + H2 -> HONO + H serve as important initiation reactions. The reactions O2 + H <- -> OH + O, H2 + O <- -> OH + H, and 2NO2 -> 2NO + O2 are significant but of lesser importance. In reducing the mechanism, the steady-state assumptions for the intermediates O, H, and OH are shown to be good; however, their use is limited because the H and OH balance relations are dominated by the same reactions. Despite these limitations, an asymptotic description of the flame structure using a one-step approximation to the kinetics is still able to predict the burning rate within a factor of three of the numerical result using the full mechanism.