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Fully-modulated, turbulent diffusion flames in microgravity
J.C. Hermanson, , H. Johari, D.P. Stocker, U.G. Hegde
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Pulsed, turbulent jet diffusion flames were studied experimentally in normal and microgravity. In all cases, the flames were fully-modulated. Fully-modulated flames have previously shown a decrease in mean flame length of ≤ 70% compared with a steady, turbulent flame. Unheated pure ethylene fuel or 50% C2H4/50% N2 was injected using a 2 mm dia nozzle into a combustor with an air or 30% O2/70% N2 co-flow at 1 atm. Microgravity conditions were achieved for ≤ 5.18 sec in drop tower rests. The removal of buoyancy by conducting experiments in microgravity had a significant effect on the structure of fully-modulated flames. In both normal gravity and microgravity, for short injection times, compact, pufflike structures were generated. More elongated flame structures, with a flame length closer to that of steady-state flames, occurred for longer injection times of ≤ 300 msec. The flame length of isolated, compact puffs was not strongly dependent on the presence of buoyancy. The most marked increase in flame length due to the removal of buoyancy in microgravity occurred for flames with short injection times and high duty cycle. A smaller increase was seen for flames with elongated structures and for steady, state flames. The changes in flame length with injection duty cycle were partly ascribed to the duty cycle at the flame tip being significantly greater than that at injection. Original is an abstract.
About the journal
JournalInternational Symposium on Combustion Abstracts of Works-in-Progress Posters