부력의 영향을 최소화한 조건에서 대향류 확산화염의화염 소화에 관한 실험적 연구
Experimental Study on Flame Extinction in Buoyancy-minimized Counterflow Diffusion Flame
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Experiments were conducted to clarify role of the outermost edge flame on low-strain-rate flame extinctionin buoyancy-suppressed non-premixed methane flames diluted with He and N2. The use of He curtain flowproduced a microgravity level of 10-2-10-3g in N2- and He-diluted non-premixed counterflow flame experiments. The critical He and N2 mole fractions at extinction with a global strain rate were examined at various burnerdiameters (10, 20, and 25 mm). The results showed that the extinction curves differed appreciably with burnerdiameter. Before the turning point along the extinction curve, low-strain-rate flames were extinguished viashrinkage of the outermost edge flame with and without self-excitation. High-strain-rate flames were extinguishedvia a flame hole while the outermost edge flame was stationary. These characteristics could be identifiedby the behavior of the outermost edge flame. The results also showed that the outermost edge flame was notinfluenced by radiative heat loss but by convective heat addition and conductive heat losses to the ambientHe curtain flow. The numerical results were discussed in detail. The self-excitation before the extinction ofa low-strain-rate flame was well described by a dependency of the Strouhal number on global strain rate andnormalized nozzle exit velocity.
Abstract
Experiments were conducted to clarify role of the outermost edge flame on low-strain-rate flame extinctionin buoyancy-suppressed non-premixed methane flames diluted with He and N2. The use of He curtain flowproduced a microgravity level of 10-2-10-3g in N2- and He-diluted non-premixed counterflow flame experiments. The critical He and N2 mole fractions at extinction with a global strain rate were examined at various burnerdiameters (10, 20, and 25 mm). The results showed that the extinction curves differed appreciably with burnerdiameter. Before the turning point along the extinction curve, low-strain-rate flames were extinguished viashrinkage of the outermost edge flame with and without self-excitation. High-strain-rate flames were extinguishedvia a flame hole while the outermost edge flame was stationary. These characteristics could be identifiedby the behavior of the outermost edge flame. The results also showed that the outermost edge flame was notinfluenced by radiative heat loss but by convective heat addition and conductive heat losses to the ambientHe curtain flow. The numerical results were discussed in detail. The self-excitation before the extinction ofa low-strain-rate flame was well described by a dependency of the Strouhal number on global strain rate andnormalized nozzle exit velocity.
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