予混合火炎の不安定性に及ぼす熱損失効果

Abstract

The effect of heat loss on the instability of premixed flames is studied by two-dimensional unsteady calculations of reactive flows, based on the compressible Navier-Stokes equation. We take account of hydrodynamic and diffusive-thermal effects as to the intrinsic instability of premixed flames. A sufficiently small disturbance is superimposed on a planar flame to obtain the relation between the growth rate and the wave number. As the heat loss becomes larger, the growth rate decreases and the unstable range narrows. This is because that the hydrodynamic instability generated by thermal expansion becomes weaker. To study the unstable behavior of cellular flames, the disturbance with the linearly most unstable wave number, i.e., the critical wave number, is superimposed. The superimposed disturbance evolves, and the cellular-flame front is formed, owing to intrinsic instability. The lateral movement of cellular flames is observed at low Lewis numbers, and the behavior of cellular-flame fronts becomes more unstable for non-adiabatic flames. With an increase in the heat loss, the burning velocity of a cellular flame normalized by that of a planar flame increases at Lewis numbers lower than unity. When the Lewis number is not less than unity, on the other hand, the flame-velocity increment decreases by increasing the heat loss.