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Forthcoming orbital experiments with the flat porous circular 25 mm diameter burner (Burning Rate Emulator) are replicated in numerical simulations of diffusion flames of ethylene and methane burning in air. The main objective is to assess the expected flame dynamics and stability, and to scrutinize the event of extinction of the unstrained diffusion flame in microgravity. For the initial period of flame development, predicted flame dynamics and the net heat flux at the burner surface are shown to be consistent with the drop tower tests performed earlier. For the longer time period to be investigated in the orbital experiments, no steady state has been predicted neither for ethylene no methane microgravity flames. Instead, the simulations have shown that flame development above the BRE burner proceeds in two consecutive modes. First, a hemispherical diffusion flame forms and expands towards a nearly spherical shape. The second mode is the evolution of the partially extinguished flame. The onset of local extinction is predicted close to the top of the spherical flame, and subsequent flame evolution is shown to depend on the fuel supply rate. In case of a small fuel supply rate, the flame self-extinguishes after several oscillations. For a higher fuel supply rate, local extinction is followed by strong re-ignition that manifests itself as an upward propagation of the triple (or hook-like) flame followed by a bright flash at the top of the flame just before complete self-extinguishment. Both symmetric and asymmetric configurations are possible. The driving force of flame extinction is the excessive radiative heat loss rate that is not compensated by the heat release rate in the reaction zone. The ethylene flames exist for a longer time period than the methane flames, in spite of comparable radiative emission. The flames produced by a lower fuel supply rate are shown to be more stable and it could exist for a longer time. The simulations have shown that gas radiation dominates over that of soot. When the classical WSGG model is applied to evaluate the effective absorption coefficient of the gaseous combustion products, selection of the mean radiation pathlength strongly affects the prediction of radiative emission from flame and its lifetime prior to extinction.
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International Seminar on Fire and Explosion Hazards (9; 2019; Saint Petersburg, Russia). Proceedings of the Ninth International Seminar on Fire and Explosion Hazards [Электронный ресурс]. Vol. 1: 21-26 April 2019, Saint Petersburg, Russia / Peter the Great St. Petersburg Polytechnic University, Autonomous Non-Profit Organization "Fire and Explosion Safety", Gefest Holding Ltd ; [edited by A. Snegirev [et al.]. — Электрон. текстовые дан. (1 файл : 118 Мб). — Saint Petersburg, 2019. — Загл. с титул. экрана. — Свободный доступ из сети Интернет (чтение, печать, копирование). — Adobe Acrobat Reader 7.0. — <URL:http://elib.spbstu.ru/dl/2/k19-45.pdf>. — <URL:http://doi.org/10.18720/SPBPU/2/k19-45>.
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