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Journal ArticleDOI

Flame spread over thin fuels in actual and simulated microgravity conditions

TL;DR: In this article, two sets of experiments are described, one involving flame spread in a Narrow Channel Apparatus (NCA) in normal gravity, and the other taking place in actual microgravity.
About: This article is published in Combustion and Flame.The article was published on 2009-06-01. It has received 76 citations till now. The article focuses on the topics: Premixed flame & Diffusion flame.
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Journal ArticleDOI
Osamu Fujita1
01 Jan 2015
TL;DR: In this paper, the authors introduce fire safety standards for flammability evaluation of solid material intended for use in a spacecraft habitat, and the difference between the limiting value in microgravity and the indices given by the standard test methods on the ground is discussed.
Abstract: This paper introduces fire safety standards for flammability evaluation of solid material intended for use in a spacecraft habitat. Two types of existing standards include material evaluation by pass/fail criteria corresponding to Test 1 of NASA STD 6001B and evaluation by a flammability index such as maximum oxygen concentration (MOC) corresponding to the improved Test 1. The advantage of the latter is the wide applicability of the MOC index to different atmospheres in spacecraft. Additionally, the limiting oxygen index (LOI) method is introduced as a potential alternative index for the evaluation using the improved Test 1 method. When criteria based on an index such as MOC or LOI are applied for material screening, the discrepancy of the index to the actual flammability limit in microgravity such as minimum limiting oxygen concentration (MLOC) is essential information for guaranteeing fire safety in space because material flammability can be higher in microgravity. In this paper, the existing research on the effects of significant parameters on material flammability in microgravity are introduced, and the difference between the limiting value in microgravity and the indices given by the standard test methods on the ground is discussed. Finally, on-going efforts to develop estimation methods of material flammability in microgravity according to normal gravity tests are summarized.

74 citations

Journal ArticleDOI
TL;DR: In this article, the authors revisited the problem of opposed fire spread under limited and excessive oxygen supply and reviewed various near-limit fire phenomena, as recently observed in flaming, smoldering, and glowing spread under various environment and fuel configurations.

40 citations

Journal ArticleDOI
TL;DR: In this article, a series of experiments in a thin layer geometry performed at the HYKA test site of the KIT were performed in a rectangular chamber with dimensions of 200 × 900 x h mm3, where h is the thickness of the layer (h = 1, 2, 4, 6, 8, 10mm).

22 citations

Journal ArticleDOI
TL;DR: In this paper, the formation of a fingering pattern caused by an instability mechanism is studied. But the authors focus on the formation only on the case when the Lewis number is well below unity.

21 citations

Journal ArticleDOI
TL;DR: In this article, the authors investigated flame spread and extinction over a PMMA in purely opposed and concurrent flows by conducting systematical experiments in a narrow channel apparatus and found that the opposed flame is much faster than the concurrent flame at a given flow velocity.
Abstract: Flame spread and extinction phenomena over a thick PMMA in purely opposed and concurrent flows are investigated by conducting systematical experiments in a narrow channel apparatus. The present tests focus on low-velocity flow regime and hence complement experimental data previously reported for high and moderate velocity regimes. In the flow velocity range tested, the opposed flame is found to spread much faster than the concurrent flame at a given flow velocity. The measured spread rates for opposed and concurrent flames can be correlated by corresponding theoretical models of flame spread, indicating that existing models capture the main mechanisms controlling the flame spread. In low-velocity gas flows, however, the experimental results are observed to deviate from theoretical predictions. This may be attributed to the neglect of radiative heat loss in the theoretical models, whereas radiation becomes important for low-intensity flame spread. Flammability limits using oxygen concentration and flow velocity as coordinates are presented for both opposed and concurrent flame spread configurations. It is found that concurrent spread has a wider flammable range than opposed case. Beyond the flammability boundary of opposed spread, there is an additional flammable area for concurrent spread, where the spreading flame is sustainable in concurrent mode only. The lowest oxygen concentration allowing concurrent flame spread in forced flow is estimated to be approximately 14 % O-2, substantially below that for opposed spread (18.5 % O-2).

21 citations


Cites background or result from "Flame spread over thin fuels in act..."

  • ...It is worth to note that various authors (Ivanov et al. 1999; Olson et al. 2009; Xiao et al. 2010; Zhang and Yu 2011) have utilized the narrow-channel type apparatus to suppress buoyancy and in effect capture the essential features of microgravity flame spread....

    [...]

  • ...Such a pyrolysis temperature value is consistent with those used in the literature (Bhattacharjee et al. 1996; Olson et al. 2009)....

    [...]

References
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Book
01 Jan 1961
TL;DR: The second edition of this book has been in short supply for some time and the authors have decided in favor of a reprint of the book rather than an extensive revision at this time.
Abstract: For some time copies of the second edition of this book have been in short supply. In order to meet, the demand for additional copies the authors have decided in favor of a reprint of the book rather than an extensive revision at this time. The justification for this lies in the character of the book. It was conceived as an exposition of basic concepts of gaseous combustion phenomena. Since the publication of the second edition in 1961 the literature on the subject has grown in volume very greatly. However, virtually no new concepts in gaseous combustion have evolved. For this reason we feel that the book, in its present form, continues to serve well the purpose for which it was intended, namely, to provide a systematic presentation of the fundamentals of combustion for scientists and engineers. In addition, we feel that the present edition has not yet outlived its usefulness as a source of data. Furthermore, the utility of certain concepts is only now beginning to be appreciated. This applies in particular to the concept of flame stretch which permits a unified approach to seemingly widely different sets of phenomena, including ignition, flame extinction, stabilization, quenching, flammability limits, and maximum heat release rates.

1,857 citations

Journal ArticleDOI
TL;DR: In this paper, a theoretical analysis of diffusion flame extinction in the stagnation point region of a condensed fuel has been made including radiative heat loss from the fuel surface, and the extinction boundary consists of a blowoff and a radiative extinction branch.

187 citations

Journal ArticleDOI
TL;DR: In this article, a flame spread map is presented which indicates three distinct regions where different mechanisms control the flame spread process: near-quenching region, very low characteristic relative velocities, a new controlling mechanism for flame spread - oxidizer transport-limited chemical reaction - is proposed.
Abstract: Microgravity tests varying oxygen concentration and forced flow velocity have examined the importance of transport processes on flame spread over very thin solid fuels. Flame spread rates, solid phase temperature profiles and flame appearance for these tests are measured. A flame spread map is presented which indicates three distinct regions where different mechanisms control the flame spread process. In the near-quenching region (very low characteristic relative velocities) a new controlling mechanism for flame spread - oxidizer transport-limited chemical reaction - is proposed. In the near-limit, blowoff region, high opposed flow velocities impose residence time limitations on the flame spread process. A critical characteristic relative velocity line between the two near-limit regions defines conditions which result in maximum flammability both in terms of a peak flame spread rate and minimum oxygen concentration for steady burning. In the third region, away from both near-limit regions, the flame spread behavior, which can accurately be described by a thermal theory, is controlled by gas-phase conduction.

142 citations

Journal ArticleDOI
TL;DR: In this article, the authors quantitatively verify a model based on diffusion limited transport and show that the finger width is determined by the degree two dimensionality of the finger tip and the finger spacing between fingers can be determined by Peclet number.
Abstract: A thin solid (e.g., paper), burning against an oxidizing wind, develops a fingering instability with two decoupled length scales. The spacing between fingers is determined by the Peclet number (ratio between advection and diffusion). The finger width is determined by the degree two dimensionality. Dense fingers develop by recurrent tip splitting. The effect is observed when vertical mass transport (due to gravity) is suppressed. The experimental results quantitatively verify a model based on diffusion limited transport.

111 citations

Journal ArticleDOI
TL;DR: A detailed description of how microgravity conditions are obtained in various facilities available to researchers (e.g., drop towers, low-gravity aircraft flying Keplerian trajectories, Space Shuttle, International Space Station) is provided in this paper.
Abstract: Microgravity Combustion brings together, for the first time, a large and growing literature on combustion in microgravity, as collated and described by recognized experts in the field of combustion science, who are active in the specialty of combustion science in microgravity. Surprisingly, no one has provided a detailed description of how microgravity conditions are obtained in the various facilities available to researchers (e.g. drop towers, low-gravity aircraft flying Keplerian trajectories, Space Shuttle, International Space Station). This is provided in the book. The book also stresses the importance of forces and transport phenomena often neglected (sometimes without justification) in combustion processes, because these neglected or weak forces become apparent when the masking effects of buoyancy are eliminated. These forces are generally poorly taught or described in the previous literature. Examples include thermal radiative heat transfer from small flames, thermophoresis, thermocapillary flows, and purely diffusive transport. It also answers long-held questions about flammability in spacecraft. It was once thought that there would be no flammability limits in microgravity, but such limits are in fact observed and now predicted experimentally.

110 citations