Theory of opposed-flow flame spread
TL;DR: A critical, historical review of the flame spread literature is given in this article, beginning with the first systematic studies of opposed-flow flame spread, including qualitative, simplified, and comprehensive numerical modeling.
Abstract: A critical, historical review of the flame spread literature is given, beginning with the first systematic studies of opposed-flow flame spread. Important modeling effects are described, including qualitative, simplified, μg and comprehensive numerical modeling. A brief discussion of subjects with the potential for further development is also given. Although this review focuses on flame-spread theory the emphasis is on the logical development, not the detailed mathematics.
Citations
More filters
01 Jan 2007
TL;DR: In this paper, the propagation speed of tribrachial flames is discussed for flames propagating in mixing layers, including the effects of concentration gradient, velocity gradient, and burnt gas expansion.
Abstract: A tribrachial (or triple) flame is one kind of edge flame that can be encountered in nonpremixed mixing layers, consisting of a lean and a rich premixed flame wing together with a trailing diffusion flame all extending from a single point. The flame could play an important role on the characteristics of various flame behaviors including lifted flames in jets, flame propagation in two-dimensional mixing layers, and autoignition fronts. The structure of tribrachial flame suggests that the edge is located along the stoichiometric contour in a mixing layer due to the coexistence of all three different types of flames. Since the edge has a premixed nature, it has unique propagation characteristics. In this review, the propagation speed of tribrachial flames will be discussed for flames propagating in mixing layers, including the effects of concentration gradient, velocity gradient, and burnt gas expansion. Based on the tribrachial edge structure observed experimentally in laminar lifted flames in jets, the flame stabilization characteristics including liftoff height, reattachment, and blowout behaviors and their buoyancy-induced instability will be explained. Various effects on liftoff heights in both free and coflow jets including jet velocity, the Schmidt number of fuel, nozzle diameter, partial premixing of air to fuel, and inert dilution to fuel are discussed. Implications of edge flames in the modeling of turbulent nonpremixed flames and the stabilization of turbulent lifted flames in jets are covered.
267 citations
TL;DR: In this article, the stabilization mechanism of lifted flames in a laminar non-premixed jet has been analyzed and experimentally investigated, and an analysis on the flame response by the perturbation from the tribrachial location shows that the lifted flame is unstable for Sc
Abstract: The stabilization mechanism of lifted flames in a laminar nonpremixed jet has been analyzed and experimentally investigated. An analysis on the flame response by the perturbation from the tribrachial location shows that the lifted flame is unstable for Sc
222 citations
TL;DR: In this article, the authors investigated the characteristics of propagating tribrachial flames in non-premixed laminar jets and found that the edge of the propagating flame has a tribarachial flame structure.
Abstract: The characteristics of propagating tribrachial flames in non-premixed laminar jets have been investigated experimentally. Free jets of methane are ignited downstream with a Nd:YAG laser to eliminate possible flow disturbances during ignition. The flame propagation is visualized and its speed measured by a high-speed shadowgraphy and schlieren technique. Results show that the edge of the propagating flame in a laminar jet regime has a tribrachial flame structure: a lean premixed flame, a rich premixed flame, and a diffusion flame, all extending from a single location. The flame displacement speed maintains a constant value for a specified flow rate and decreases with jet velocity. Flame propagation speeds of tribrachial flames have been determined from the velocity fields measured by laser Doppler velocimetry and from jet velocity modeling. This flame speed correlates well with flame curvature and mixture fraction gradient. It is found that the unsteady curvature term dominates over the steady curvature term in flame stretch and that the flame propagation speed correlates well and decreases with flame stretch.
172 citations
TL;DR: A review of modeling and experiments of the ignition and flame spread over liquid fuel pools for separate regimes defined by the initial pool temperature relative to the fuel flash point is given in this paper.
Abstract: This article is a review of modeling and experiments of the ignition and flame spread over liquid fuel pools for separate regimes defined by the initial pool temperature relative to the fuel flash point. The purpose of this review is twofold. First it will emphasise newer or lesser known studies, both experimental and numerical, because these may question or alter some of the conclusions from the last review of the field by Glassman and Dryer, published in 1981. Second, it will cover the additional subjects of ignition susceptibility, analytic and numerical modeling, non-air atmospheres and forced flow, beds of fuel-soaked sand or glass beads and buoyancy-related processes applicable to microgravity combustion science and spacecraft fire safety. The review concludes with recommendations for further numerical and experimental research.
130 citations
01 Jan 2016
TL;DR: This chapter will describe how heating of a solid fuel leads to flaming ignition and the presence of a source of heat decoupled from the solid and fuel gasification will be assumed throughout the chapter.
Abstract: This chapter will describe how heating of a solid fuel leads to flaming ignition. The discussion will be centred on flaming ignition of solid fuels but will not address smouldering or spontaneous ignition since these subjects will be covered in Chaps. 19 and 20 respectively. Thus, the presence of a source of heat decoupled from the solid and fuel gasification will be assumed throughout the chapter.
92 citations
Cites methods from "Theory of opposed-flow flame spread..."
...To avoid the complex form of the error function simplified solutions have been proposed in the literature [70, 71]....
[...]
References
More filters
9,185 citations
Book•
31 Aug 1982TL;DR: In this paper, the premixed plane flame is defined as a mixture of spherical and cylindrical premixed flames, and the theory of multidimensional theory of premixed flame is presented.
Abstract: 1. Governing equations of combustion 2. The premixed plane flame 3. Perturbations: SVFs and NEFs 4. Steady burning of a linear condensate 5. Unsteady burning of a linear condensate 6. Spherical diffusion flames 7. Cylindrical and spherical premixed flames 8. Multidimensional theory of premixed flames 9. Burners 10. Effects of shear and strain 11. Stability 12. Ignition and explosion.
541 citations
TL;DR: In this article, the authors focus on the coupled chemical and physical processes involved in self-sustained propagation of smoldering and conclude that even for the most-studied case of cellulose, the chemical mechanisms involved in these processes are both too complex and too poorly understood to be included in a smolder propagation model.
Abstract: Smoldering combustion of various natural and synthetic solid materials constitutes a substantial fire hazard; the process itself produces copious toxic gases and it can lead to flaming combustion. This review focuses on the coupled chemical and physical processes involved in self-sustained propagation of smoldering. The potential heat sources (gas-phase oxidation, oxidative polymer degradation. char oxidation) are examined, along with the heat sinks (polymer pyrolysis, water vaporization). It is concluded that, even for the most-studied case of cellulose, the chemical mechanisms involved in these processes are both too complex and too poorly understood to be included in a smolder propagation model. Greatly simplified kinetic schemes are currently inevitable; the kinetic parameters are empirical and of restricted usefulness. A general model of the thermophysics of propagation (for arbitrary chemistry) is presented as a benchmark against which to compare existing models. The general case, with gradients both on the scale of the particles that comprise the fuel and on the scale of the overall combustion wave moving through the fuel bed, is too complex to be tractable. The general model equations are non-dimensionalized: simplifications are noted in the limit of small or large values for certain dimensionless groups. Existing smolder propagation models in the literature are reviewed; all represent great simplifications of the general case and none closely describes a realistic smoldering fire hazard. The principal usefulness of existing models is in rationalizing certain experimentally-observed trends. Truly useful predictive models of realistic hazard situations remain to be developed.
427 citations