ASYMPTOTIC AND NUMERICAL-ANALYSIS OF A PREMIXED LAMINAR NITROGEN DIOXIDE-HYDROGEN FLAME

A kinetic mechanism of eighty-some reactions for flames in mixtures of hydrogen and nitrogen dioxide is systematically reduced to twenty-fou r-, eleven-, seven-, two-, and one-step mechanisms. The numerically pr edicted burning rates for the full mechanism describing a near-stoichi ometric: burner-stabilized flame at a pressure of 25 torr, and final t emperature of 2000 K are compared with the results using the reduced m echanisms, and the sources of inaccuracies are identified. The two rea ctions NO2 + H --> NO + OH and H-2 + OH reversible arrow H2O + H accou nt for about 97% of the NO2 and H-2 consumption and NO and H2O product ion, and are the principal reactions involving OH and H atoms. The rea ctions 2OH reversible arrow H2O + O and NO2 + O --> NO + O-2 are impor tant for OH and O, while the reactions NO2 + M --> NO + O + M and NO2 + H-2 --> HONO + H serve as important initiation reactions. The reacti ons O-2 + H reversible arrow OH + O, H-2 + O reversible arrow OH + H, and 2NO(2) --> 2 NO + O-2 are significant but of lesser importance. In reducing the mechanism, the steady-state assumptions for the intermed iates 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 reac tions. As a result of these limitations, an asymptotic description of the flame structure using a one-step approximation to the kinetics is only able to predict the burning rate within a factor of three of the numerical result using the full mechanism.