The effects of radiative heat loss on the diffusive-thermal instability of high-temperature premixed flames

The effects of radiative heat loss on the diffusive-thermal instability of high-temperature premixed flames were investigated by two-dimensional unsteady calculations of reactive flows, based on the diffusive-thermal model equation, under the conditions of constant enthalpy. As the unburned-gas temperature became higher, the growth rate increased and the unstable range widened at Lewis numbers lower than unity, which was due mainly to the increase of the burning velocity of a planar flame. As for the growth rate and unstable range normalized by the burning velocity of a planar flame, the former decreased and the latter narrowed. This was due to the reduction of Zeldovich numbers. In addition, the normalized growth rate increased and the normalized unstable range widened as the radiative heat loss became larger. This indicated that the radiative heat loss had a pronounced influence on the diffusive-thermal instability of high-temperature premixed flames. Moreover, cellular-flame fronts formed owing to diffusive-thermal instability. The normalized burning velocity of a cellular flame decreased as the unburned-gas temperature became higher, and increased as the radiative heat loss became larger.