Instability of Hydrogen-Air Premixed Flames with Heat Loss

Abstract

The instability of hydrogen-air premixed flames with heat loss has been investigated by two-dimensional, unsteady calculations of reactive flows. The numerical model containing the detailed hydrogen-oxygen combustion with 17 elementary reactions of 8 reactive species and a nitrogen diluent, compressibility, viscosity, heat conduction, molecular diffusion, and heat loss of Newtonian type was used. Estimating the diffusive-thermal effect on the instability of premixed flames, the equivalence ratio was varied 0.75 to 1.25. A sufficiently small disturbance was superimposed on a planar flame to obtain the dispersion relation and linearly most unstable wave number. To invistigate the characteristics of cellular flames, the disturbance with the linearly most unstable wave number, i.e. the critical wave number, was superimposed. The superimposed disturbance evolves owing to intrinsic instability, and then the cellular-flame front forms. With an increase in the heat-loss parameter, the burning velocity of a cellular flame becomes monotonously smaller, which is due to the decrease in thermal expansion. However, the burning velocity of a cellular flame normalized by that of a planar flame at equivalence ratios lower than unity becomes larger near the quenching point.