Radiation induced instability of stretched premixed flames

Unsteady propagation and instability of radiative stretched premixed flames at Lewis numbers close to unity were numerically investigated using helium diluted counterflow methane flames, with the interest on understanding the stability of three near-limit and sub-limit multiple flame regimes, i.e., the near stagnation flame, the weak flame, and the distant flame. The near-limit and sub-limit near-stagnation flames were stable close to the flammability limit, and that a new mode of oscillation instability existed at equivalence ratios sufficiently larger than the flammability limit. Stability of the weak and the distant flame, and jump from the weak flame to the normal flame, were observed. A comparison of the present prediction with the microgravity experimental observation showed qualitative agreement on the oscillation frequency and region for the occurrence of oscillation. Calculations for Lewis numbers larger and smaller than unity showed that the radiation induced instability was a physically intrinsic phenomenon for radiative stretched premixed flames. A satisfactory explanation for the microgravity observation was provided. Original is an abstract.