Critical temperature and reactant mass flux for radiative extinction of ethylene microgravity spherical diffusion flames at 1 bar |
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| Institution: | 1. Department of Energy, Environmental & Chemical Engineering, Washington University in St. Louis, St. Louis, MO 63130, USA;2. Department of Fire Protection Engineering, University of Maryland, College Park, MD 20742, USA;3. Department of Electronics and Information Systems, Ghent University, Building S-8, Krijgslaan 281, B-9000, Gent, Belgium;1. NASA Glenn Research Center, 21000 Brookpark Rd., Cleveland, OH 44135, United States;2. Case Western Reserve University, 10900 Euclid Ave, Cleveland, OH 44106, United States;3. ESA/ESTEC, Keplerlaan 1, Postbus 299, Noordwijk, AG 2200, the Netherlands;4. Slovenian National Building and Civil Engineering Institute (ZAG) Dimi?eva Ulica 12, FRISSBE, Ljubljana 1000, Slovenia;5. University of California, Berkeley, CA 94720-1740, United States;7. University College London, Gower Street, London WC1E 6BT, United Kingdom;8. Hokkaido University, Kita 8, Nishi 5, Kita-ku, Sapporo, Hokkaido 060-0808, Japan;9. Moscow M.V. Lomonosov State University, Leninskie Gory, 1, Moscow 119992, Russian Federation;10. Federal Science Center “Scientific Research Institute for System Analysis of the Russian Academy of Sciences” Nakhimovskiy 36-1, Moscow 117238, Russian Federation;11. School of Engineering, University of Edinburgh, Edinburgh, UK;1. Department of Mechanical Engineering, Yamaguchi University, Japan;2. Japan Aerospace Exploration Agency, Japan;3. NASA Glenn Research Center, United States;1. Institute for Combustion Technology, RWTH Aachen University, Aachen 52056, Germany;2. National Institute of Standards and Technology, Gaithersburg, MD, USA;1. Fire Safety Research Institute UL, 6200 Old Dobbin Ln., Columbia, MD 2104, USA;2. Department of Fire Protection Engineering, University of Maryland, College Park, MD 20742, USA;1. Department of Energy, Environmental, & Chemical Engineering, Washington University in St. Louis, 1 Brookings Drive, St. Louis, MO 63130, USA;2. Cabot Corporation, 157 Concord Rd., Billerica, MA 01821, USA |
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| Abstract: | In microgravity combustion, where buoyancy is not present to accelerate the flow field and strain the flame, radiative extinction is of fundamental importance, and has implications for spacecraft fire safety. In this work, the critical point for radiative extinction is identified for normal and inverse ethylene spherical diffusion flames via atmospheric pressure experiments conducted aboard the International Space Station, as well as with a transient numerical model. The fuel is ethylene with nitrogen diluent, and the oxidizer is an oxygen/nitrogen mixture. The burner is a porous stainless-steel sphere. All experiments are conducted at constant reactant flow rate. For normal flames, the ambient oxygen mole fraction was varied from 0.2 to 0.38, burner supply fuel mole fraction from 0.13 to 1, total mass flow rate, ?total, from 0.6 to 12.2 mg/s, and adiabatic flame temperature, Tad, from 2000 to 2800 K. For inverse flames, the ambient fuel mole fraction was varied from 0.08 to 0.12, burner supply oxygen mole fraction from 0.4 to 0.85, ?total from 2.3 to 11.3 mg/s, and Tad from 2080 to 2590 K. Despite this broad range of conditions, all flames extinguish at a critical extinction temperature of 1130 K, and a fuel-based mass flux of 0.2 g/m2-s for normal flames, and an oxygen-based mass flux of 0.68 g/m2-s for inverse flames. With this information, a simple equation is developed to estimate the flame size (i.e., location of peak temperature) at extinction for any atmospheric-pressure ethylene spherical diffusion flame given only the reactant mass flow rate. Flame growth, which ultimately leads to radiative extinction if the critical extinction point is reached, is attributed to the natural development of the diffusion-limited system as it approaches steady state and the reduction in the transport properties as the flame temperature drops due to increasing flame radiation with time (radiation-induced growth.) |
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