Radiative Extinction of Laminar Diffusion Flame above the Flat Porous Burner in Microgravity: A Computational Study
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Radiative Extinction of Laminar Diffusion Flame above the Flat Porous Burner in Microgravity: A Computational Study E. A. Kuznetsova , A. Yu. Snegireva , and E. S. Markusa
UDC 536.46
Published in Fizika Goreniya i Vzryva, Vol. 56, No. 4, pp. 26–45, July–August, 2020. Original article submitted December 23, 2019; revision submitted February 19, 2020; accepted for publication February 19, 2020.
Abstract: Transient dynamics of formation and extinction of methane- and ethylene-fueled flames above the flat porous burner in an oxidizing atmosphere is numerically investigated. The simulated scenarios replicate the experimental conditions of the BRE (Flamenco) project of the ACME program focusing on combustion research in microgravity. The 3D unsteady model includes the multistep and multi-component chemical mechanisms of fuel oxidation, formation and oxidation of soot, and the radiative transfer. The model is validated for the methane-fueled jet laminar diffusion flame in normal gravity and for the ethylene flame developing in short-duration free-fall microgravity in the drop tower. The microgravity flames are then simulated at longer times, and the range of fuel mass fluxes characteristic of solid and liquid combustibles is explored. In all the cases considered, combustion is essentially unsteady, in spite of the constant fuel supply rate. During the initial stage of flame growth, the temperature in the reaction zone persistently decreases due to the radiative losses down to the level causing local extinction, oscillations, and complete extinguishment of the flame. The effect of fuel type and mass flux at the burner surface on the flame lifetime and on its disintegration dynamics is demonstrated. The sensitivity of the results to the chemical mechanism used in the simulations is examined. The radiative fraction in the microgravity flames is found to be by an order of magnitude higher than that in the normal gravity flames produced by the same burner. The radiative losses are shown to be the reason for extinction and instability in the microgravity flames considered in this work. Keywords: BRE, microgravity, laminar diffusion flame, thermal radiation, extinction, radiative extinction. DOI: 10.1134/S0010508220040036
INTRODUCTION Structure, dynamics, and stability limits of a laminar diffusion flame created by the same fuel source appear to be very different in micro- and normal gravity. As an example, candle burning in microgravity revealed the following peculiarities mentioned in [1]. Being bright yellow immediately after ignition, the flames become blue and nearly hemispherical in few seconds, a
Peter the Great St. Petersburg State Polytechnic University, St. Petersburg, 195251 Russia; [email protected].
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with the much larger standoff distance from the wick. The zone of the highest heat release rate moved towards the flame tip, and the width of the reaction zone increased. It has been established that, in a quiescent and unconfined atmosphere, the candle can steadily burn for a very long time. Finally, flame extinction occurring d
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