The Instability of Flame Fronts in Premixed Combustion of Low-Temperature Gases (Effects of Unburned-Gas Temperature)

Abstract

We performed two-dimensional unsteady calculations of reactive flows, based on the compressible N-S equation, to study the effects of unburned-gas temperature on the instability of flame fronts. As the unburned-gas temperature became lower, the growth rate decreased and the unstable range narrowed. This was due mainly to the reduction of the burning velocity of a planar flame. The normalized growth rate increased with a decrease of the unburned-gas temperature, and the normalized unstable range widened at Lewis numbers smaller than unity. This was because that the thermal-expansion effects became stronger owing to the increase of the temperature ratio of burned and unburned gases, and that the diffusive-thermal effects strengthened at Lewis numbers smaller than unity owing to the increase of the Zeldovich number. Moreover, the cellular shape of flame fronts formed, which was due to intrinsic instability. The normalized burning velocity of a cellular flame increased as the unburned-gas temperature became lower, especially in premixed flames with small Lewis numbers.