Effect of Radiative Heat Loss on Diffusion Flames in Quiescent Microgravity Atmosphere

This paper presents the results of theoretical calculations for radiation-induced extinction of one-dimensional unsteady diffusion flames in a quiescent microgravity environment. The model formulation includes both gas and soot radiation. Soot volume fraction is not a priori assumed, instead it is produced and oxidized according to the temperature- and species-dependent formation and oxidation rates. Thus. soot volume fraction and the resulting flame radiation varies with space and time. Three cases arc considered: (i) a nonradiating flame, (ii) a barely sooty flame, and (iii) a very sooty flame. For the nonradiating flame, the maximum flame temperature remains constant and it docs not extinguish. However. the burning rate decreases with time (t) as t [,2 making the flame "weaker. ,. For radiating flames. the flame temperature decreases due to radiative heat loss for both barely sooting and heavily sooting flame" resulting in extinction. The decrease in the hurning rate for radiating t1 of S(lot ,1rl: formed and the radiation from S[Jot is also very large. However. this radiativl: heat loss dOl:s not cause a perceptihle local depression in the temperature profile because it is offset primarily hy thermal diffusion and to a lesser ckgree hy heat release due to soot oxidation, Later. both soot and soot radiation decrease with time. These results are consistent with the experimental observations made in microgravity spherical diffusi,)J1 flames and provide considerable insight into radiative cooling of sooty names, This work, while nut cxpcrirncIH,ll, docs shows that radiative extinction of diffusion flames in a quiescent microgravity environment is possible.