EXTINCTION OF LOW-STRETCHED DIFFUSION FLAME IN MICROGRAVITY

Extinction of counterflow diffusion flames of air and methane diluted with nitrogen is studied by drop tower experiments and numerical calcu lation using detailed chemistry and transport properties. Radiative he at loss from the flame zone is taken into consideration. Experimental results identified two kinds of extinction at the same fuel concentrat ion, that is, in addition to the widely known stretch extinction, anot her type of extinction is observed when the stretch rate is sufficient ly low: Consequently, plots of stretch rates versus fuel concentration limits exhibit a ''C-shaped'' extinction curve. Numerical calculation including radiative heat loss from the dame zone qualitatively agreed with the experimental results and indicated that the mechanism of cou nterflow diffusion dame extinction at low stretch rates was radiative heat loss. (C) 1998 by The Combustion Institute.