alexander.snegirev@ugent.be © 2022 Ghent University, Campus UFO, Technicum Blok 4 Sint-Pietersnieuwstraat 41, 9000 Gent Flame evolution modes Growing spherical segment Steady flame Unsteady transient flame Top extinction Bottom extinction Symmetric oscillations Non-symmetric oscillations Steady oscillations Full extinguishment Spiral Capuchin Incomplete recovery Incomplete recovery Complete recovery Until fuel termination Motivation and objectives What is studied? • Zero gravity diffusion flame • Very low momentum of fuel flow, Re < 10 • Flat fuel source • Stagnant atmosphere, various oxygen content Two prototypes studied to date • Jet laminar flame: larger Re • Spherical flame around a point-source (droplet or candle): much smaller size of fuel source Practicality • It is this kind of flame that develops when a condensed fuel (liquid or solid) burns • Flammability of such a condensed fuel is directly coupled with the stability of gaseous flame Objectives • To provide interpretation of the orbital experiment BRE (Flamenco), 2019-2021 • To develop the model and evaluate its capability • To explain the dramatic effects incurred by the reduced gravity • To investigate the extinction mechanism and to analyze transient flame dynamics This kind of flame has not been investigated earlier The flame of interest is dissimilar to these prototypes FIRE INCEPTION IN MICROGRAVITY ORBITAL EXPERIMENT BRE-FLAMENCO ONBOARD THE INTERNATIONAL SPACE STATION, 2019-2021 A. Snegirev Ghent University, Faculty of Engineering and Architecture Department of Structural Engineering and Building Materials (Combustion, Fire and Fire Safety) Radiative extinction • In normal and zero gravity, characteristic velocities differ by two orders of magnitude, so do the flame residence times (≈ 0.04 in 1g and 8 s in 0g) => • The radiative heat loss in zero gravity is much higher than that in normal gravity. Its ratio to the heat release rate is ≈ 0.08 (1g) and ≈ 0.7 (0g, prior to extinction) • Maximum flame temperature: ≈ 2100 K (1g) and ≈ 1200 K (0g, prior to extinction) • As a result, the zero-gravity flame cannot attain the steady state: the initial stage of the steady growth is interrupted by the local extinction followed by flame oscillation and extinguishment (unless the oxygen concentration is increased to 30-40%) The experiment 59+139 orbital tests (2019 and 2020-2021) • Oxygen mole fraction in the ambient atmosphere: 0.21-0.4 • Pressure: normal (14.3-14.7 psi) and reduced (8.1-10.3 psi) • Burner mass flux 1.5-11 g/(m2·s) • Fuels: C2H4 - N2 mixtures, CH4 - N2 mixtures (0, 33 and 50% N2) • Burners: 25-mm and 50-mm diameter Recordings and measurements • Video 30 fps • Burner surface temperatures and heat fluxes (center, off-center) • Remote radiometer (radiative fraction) • Filament temperatures • A. Snegirev, E. Kuznetsov, E. Markus, P. Dehghani, P. Sunderland, Transient dynamics of radiative extinction in low-momentum microgravity diffusion flames, Proc. Combust. Inst. 38 (2021) 4815-4823 https://doi.org/10.1016/j.proci.2020.06.110 • E. Kuznetsov, A. Snegirev, E. Markus, Radiative Extinction of Laminar Diffusion Flame above the Flat Porous Burner in Microgravity: a Computational Study, Combust. Explos. Shock Waves, 56:4 (2020) 394-411 https://doi.org/10.1134/S0010508220040036 • A. Snegirev, E. Kuznetsov, E. Markus, P. Dehghani, P. Sunderland. Transient dynamics of radiative extinction in low-momentum microgravity diffusion flames. 38th Int. Combust. Symp., Adelaide, Australia, 24 – 29 January 2021 (Paper 1J05: 19-01152 • Kuznetsov E., Snegirev A., Markus E., Radiative Extinction of a Diffusion Flame in Microgravity. Proc. Ninth International Seminar on Fire and Explosion Hazards, 21-26 April 2019, St. Petersburg, Russia, SPbPU, 2019, Vol. 1, pp. 214-224 http://doi.org/10.18720/spbpu/2/k19-73 Publications • A. Snegirev, On radiative extinction of microgravity diffusion flames, Combust. Flame 2022 (submitted) Approximate theory • ( ) 2 2 3 2 1 3 , ,0 , O , 4 4 O