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Journal ArticleDOI

Flame spread: Effects of microgravity and scale

TL;DR: In this paper, a large-scale flame spread experiment was conducted inside an orbiting spacecraft to study the effects of microgravity and scale and to address the uncertainty regarding how flames spread when there is no gravity and if the sample size and the experimental duration are, respectively, large enough and long enough to allow for unrestricted growth.
About: This article is published in Combustion and Flame.The article was published on 2019-01-01. It has received 59 citations till now. The article focuses on the topics: Flame spread & Spacecraft.
Citations
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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 paper, the effect of pressure and microgravity on upward/concurrent flame spread over 10 mm thick polymethyl methacrylate (PMMA) slabs was investigated and correlated in terms of a non-dimensional mixed convection analysis that describes the convective heat transferred from the flame to the solid.

30 citations

Journal ArticleDOI
TL;DR: In this article, an array of 10 1.5 cm-long 5 cm-wide filter papers is uniformly distributed on a vertical sample holder subjected to double-sided burn, and the distance between the samples was varied from 0 to 4 cm.

18 citations

Journal ArticleDOI
TL;DR: In this article, a series of microgravity experiments of concurrent-flow flame spread over samples of ultra-low area densities are conducted using NASA Glenn Research Center's Zero Gravity Research Facility (the 5.18 ǫ s drop tower).
Abstract: There are no existing experimental studies of flame spread rate trends for ultra-thin solid samples. Previous theory has predicted that for concurrent flame in kinetic regime, the flame spread rate decreases as the sample thickness decreases and there is a critical thickness below which burning is not possible. To test this hypothesis, a series of microgravity experiments of concurrent-flow flame spread over samples of ultra-low area densities are conducted using NASA Glenn Research Center’s Zero Gravity Research Facility (the 5.18 s drop tower). The tested samples are cellulose-based materials of various area densities, ranging from 0.2 mg/cm2 to 13 mg/cm2, as low as one order of magnitude less than those ever tested before. Each sample is 30 cm long by 5 cm wide and is burned in a low-speed concurrent air flow (5 to 30 cm/s). The results show that the concurrent flame spread rate is proportional to the flow velocity relative to the flame and is inversely proportional to the sample area density. A theoretical formulation, provided in this work, suggests that the flame length has a linear relationship with the relative flow speed and has no direct dependency on the sample area density. The experimental data supports this conclusion. From the images recorded in the experiments, a unique flame base tubular structure directed upstream away from the burnout zone is observed for thin samples. This structure is suspected to be due to flame stretching and localized blowoff caused by the oxidative pyrolysis Stefan flows at the sample burnout. This can be an indication that the chemical time becomes comparable to the flow time of the Stefan flow and the tested samples are approaching the kinetically-limited thickness. For the thinnest tested sample (0.2 mg/cm2), flames with concurrent and opposed dual natures are observed when the air flow rate is low (< 20 cm/s). At the lowest tested flow rate (5 cm/s), the flame spread rate exceeds the air flow rate and the flame transits to an opposed flame in the concurrent flow. The dual nature and flame transition are presented and discussed. This study provides detailed examination through high-resolution images of the transition between the concurrent to opposed flame spread modes.

17 citations

Journal ArticleDOI
TL;DR: In this paper, a flame is established over a solid cylindrical polyethylene coated metallic wire and spreads at a steady rate, in low velocity flow conditions allowed by the absence of buoyancy.
Abstract: The objective of this work is to quantify for the first time soot-related radiative heat transfer in opposed flow flame spread in microgravity. This article presents experimental results obtained in parabolic flight facilities. A flame is established over a solid cylindrical polyethylene coated metallic wire and spreads at a steady rate, in low velocity flow conditions allowed by the absence of buoyancy. Implementing the Broadband Modulated Absorption/Emission technique, the two-dimensional fields of soot volume fraction and temperature are obtained for the first time in flame spread configuration over an insulated wire in microgravity. The consistency of the results is assessed by comparing results from independent experimental runs. From these fields, radiative losses attributed to soot in the flame are computed at each location. This map of radiative losses together with the profile of the wire surface are then used as inputs to a novel experimental approach that enables the assessment of soot radiative heat feedback to the wire. Results are extracted from a specific case of a flame propagating over a polyethylene coated Nickel–Chrome wire at nominal pressure. The oxidizer, composed of 19% oxygen and 81% nitrogen in volume is blown at opposed flow parallel to the wire at a velocity of $$200\,\hbox {mm}\cdot\hbox{s}^{-1}$$. This new approach provides the first detailed quantitative measurements which are required to check the relevance of heat transfer models under development, therefore to better understand the mechanisms driving flame spread in microgravity.

17 citations

References
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Book
21 Apr 2006
TL;DR: In this article, the authors present an overview of the history of fire and its application in the field of fire safety, including a discussion of the role of mass and energy conservation in chemical reactions.
Abstract: Preface. Nomenclature. 1 Introduction to Fire. 1.1 Fire in History. 1.2 Fire and Science. 1.3 Fire Safety and Research in the Twentieth Century. 1.4 Outlook for the Future. 1.5 Introduction to This Book. 2 Thermochemistry. 2.1 Introduction. 2.2 Chemical Reactions. 2.3 Gas Mixture. 2.4 Conservation Laws for Systems. 2.5 Heat of Formation. 2.6 Application of Mass and Energy Conservation in Chemical Reactions. 2.7 Combustion Products in Fire. 3 Conservation Laws for Control Volumes. 3.1 Introduction. 3.2 The Reynolds Transport Theorem. 3.3 Relationship between a Control Volume and System Volume. 3.4 Conservation of Mass. 3.5 Conservation of Mass for a Reacting Species. 3.6 Conservation of Momentum. 3.7 Conservation of Energy for a Control Volume. 4 Premixed Flames. 4.1 Introduction. 4.2 Reaction Rate. 4.3 Autoignition. 4.4 Piloted Ignition. 4.5 Flame Speed, Su. 4.6 Quenching Diameter. 4.7 Flammability Limits. 4.8 Empirical Relationships for the Lower Flammability Limit. 4.9 A Quantitative Analysis of Ignition, Propagation and Extinction. 5 Spontaneous Ignition. 5.1 Introduction. 5.2 Theory of Spontaneous Ignition. 5.3 Experimental Methods. 5.4 Time for Spontaneous Ignition. 6 Ignition of Liquids. 6.1 Introduction. 6.2 Flashpoint. 6.3 Dynamics of Evaporation. 6.4 Clausius-Clapeyron Equation. 6.5 Evaporation Rates. 7 Ignition of Solids. 7.1 Introduction. 7.2 Estimate of Ignition Time Components. 7.3 Pure Conduction Model for Ignition. 7.4 Heat Flux in Fire. 7.5 Ignition in Thermally Thin Solids. 7.6 Ignition of a Thermally Thick Solid. 7.7 Ignition Properties of Common Materials. 8 Fire Spread on Surfaces and Through Solid Media. 8.1 Introduction. 8.2 Surface Flame Spread - The Thermally Thin Case. 8.3 Transient Effects. 8.4 Surface Flame Spread for a Thermally Thick Solid. 8.5 Experimental Considerations for Solid Surface Spread. 8.6 Some Fundamental Results for Surface Spread. 8.7 Examples of Other Flame Spread Conditions. 9 Burning Rate. 9.1 Introduction. 9.2 Diffusive Burning of Liquid Fuels. 9.3 Diffusion Flame Variables. 9.4 Convective Burning for Specific Flow Conditions. 9.5 Radiation Effects on Burning. 9.6 Property Values for Burning Rate Calculations. 9.7 Suppression and Extinction of Burning. 9.8 The Burning Rate of Complex Materials. 9.9 Control Volume Alternative to the Theory of Diffusive Burning. 9.10 General Considerations for Extinction Based on Kinetics. 9.10.1 A demonstration of the similarity of extinction in premixed and diffusion flames. 9.11 Applications to Extinction for Diffusive Burning. 10 Fire Plumes. 10.1 Introduction. 10.2 Buoyant Plumes. 10.3 Combusting Plumes. 10.4 Finite Real Fire Effects. 10.5 Transient Aspects of Fire Plumes. 10.5.1 Starting plume. 10.5.2 Fireball or thermal. 11 Compartment Fires. 11.1 Introduction. 11.2 Fluid Dynamics. 11.3 Heat Transfer. 11.4 Fuel Behavior. 11.5 Zone Modeling and Conservation Equations. 11.6 Correlations. 11.7 Semenov Diagrams, Flashover and Instabilities. 12 Scaling and Dimensionless Groups. 12.1 Introduction. 12.2 Approaches for Establishing Dimensionless Groups. 12.3 Dimensionless Groups from the Conservation Equations. 12.4 Examples of Specific Correlations. 12.5 Scale Modeling. Appendix. Flammability Properties. Archibald Tewarson. Index.

599 citations

Journal ArticleDOI
01 Jan 1969
TL;DR: In this article, a theoretical description of a laminar diffusion flame spreading against an air stream over a solid- or liquid-fuel bed is presented, where both a thin sheet and a semi-infinite fuel bed are considered.
Abstract: A theoretical description is presented for a laminar diffusion flame spreading against an air stream over a solid- or liquid-fuel bed. Both a thin sheet and a semi-infinite fuel bed are considered. The burning process is described as follows: The hot flame heats the unburned fuel bed, which subsequently vaporizes. The resulting fuel vapor reacts with the oxygen supplied by the incoming air, thereby producing the heat that maintains the flame-spread process. The formulated model treats the combustion as a diffusion flame, for which the details of the reaction kinetics can be ignored by assuming infinite reaction rates. The model includes the chemical stoichiometry, heat of combustion, gas-phase conductive heat transfer, radiation, mass transfer, fuel vaporization, and fuel-bed thermal properties. The radiation is mathematically treated as a heat loss at the flame sheet and a heat gain at the fuel-bed surface. The calculated flame-spread formulas are not inconsistent with available experimental data. These results reveal much of the physics involved in a spreading, flame. For instance, the flame-spread rate is strongly influenced by (1) the adiabatic stoichiometric flame temperature, and (2) the fuel-bed thermal properties, except for the fuel-bed conductivity parallel to the propagation direction.

356 citations

Journal ArticleDOI
TL;DR: In this paper, heat transfer and gas phase chemical kinetic aspects of the flame spread process are addressed separately for the spread of flames in oxidizing flows that oppose or concur with the direction of propagation.
Abstract: Recent advances in the experimental study of the mechanisms controlling the spread of flames over the surface of combustible solids are summarized in this work. The heat transfer and gas phase chemical kinetic aspects of the flame spread process are addressed separately for the spread of flames in oxidizing flows that oppose or concur with the direction of propagation. The realization that, in most practical situations, the spread of fire in opposed gas flows occurs at near extinction or non-propagating conditions is particularly significant. Under these circumstances, gas phase chemical kinetics plays a critical role and it must be considered if realistic descriptions of the flame spread process are attempted. In the concurrent mode of flame spread, heat transfer from the flame to the unburnt fuel appears to be the primary controlling mechanism. Although gas phase chemcial kinetics is unimportant in the flame spreading process, it is important in the establishment and extension of the diffusion ...

266 citations

Journal ArticleDOI
01 Jan 1977
TL;DR: In this paper, the authors provide a framework within which various studies can be placed, focusing on the underlying heat-transfer, fluid-flow and chemical-kinetic phenomena of fire spread.
Abstract: Mechanisms involved in many types of fire spread are described in a manner that sacrifices accuracy for the purpose of emphasizing general aspects of the underlying heat-transfer, fluid-flow and chemical-kinetic phenomena. Consideration is given to conditions for transition from one mode of propagation to another. Research on fire spread has been pursued intensively in recent years, and in the present contribution at attempt is made to provide a framework within which various studies can be placed. Entries to current literature are provided. Areas of apparent importance that do not seem to have been emphasized are suggested.

241 citations

Journal ArticleDOI
01 Jan 1979
TL;DR: In this article, the authors reviewed non-luminous radiation theories and compared them to Hottel's emmissivity charts for typical homogeneous combustion situations and concluded that the presence of luminous soot must be locally supported by chemical heat release in normal fire situations.
Abstract: Non-luminous radiation theories are reviewed and compared to Hottel's emmissivity charts for typical homogeneous combustion situations. Both narrow-band statistical and exponential wide-band models are considered. The results are then extended to luminous flames and the issue of whether flames can be regarded as gray is discussed quantitatively for various flame gases. Experimental investigations of the heat transfer components to burning fuel surfaces show that radiation is dominant at scales of 0.2–0.3 m and above. Comparative measurements of various non-charring plastic fuels show that the flame absorption-emission coefficient is the principal fuel property controlling the fuel's burning rate at hazardous scales. The measurements also indicate that the actual volumetric heat release rate is the same for different fuels burning as buoyant turbulent diffusion flames at similar scales. Concerning flame structure it is shown that the presence of luminous soot must be locally supported by chemical heat release in normal fire situations. It is also suggested that the observed proportionality of radiant heat output to fuel supply rate for geometrically similar buoyant diffusion flames is due to the insensitivity of the characteristic Kolmogorov microscale to changes in fuel flow rate. The review also discusses numerous important unresolved fire research topics.

225 citations