A numerical study about the typical opposed-jet laminar $H_2$-Air diffusion flames was done to know the structure of flame front and the chemical kinetic mechanisms. To approach the diffusion flames more-easily, the potential flow approximation was made, and rather simple 4-step hydrogen kinetics was adopted.
The ignition-extinction characteristics was also investigated with varying several external conditions.
The following 4 conclusions can be drowen from this study.
(1) As the reaction rates change from finite kinetics rates (in nonequilibrium state) to infinite reaction rates(in equilibrium state), the intermediate products becomes less, and the flame approaches flame sheet model.
(2) The condition that finite kinetics model become infinite reaction rate model is either to increase the Damkohler number(low flow velocity) or to decrease the equilibrium constants(increase pressure).
(3) The 4-step kinetics can be classified as 2 kinetic steps & 2 equilibrium steps.
(4) The increase of Lewis number, ambient pressure. the initial oxygen, hydrogen concentrations and the initial oxygen, hydrogen temperature make the flame be stabilized from the ignition-extinction characteristics of flame.
(5) additively, the equivalent single step reaction rate was derived from 4-step reversible reaction rates.
