A Numerical Study of Leading Edge Anchoring Characteristics of Ethanol Sourced Laminar Boundary Layer Diffusion Flames
14 Sep 2011-Combustion Science and Technology (Taylor & Francis Group)-Vol. 183, Iss: 10, pp 1133-1145
TL;DR: In this article, a numerical study of leading edge anchoring characteristics of diffusion flames established over a liquid ethanol film in a confined environment at atmospheric pressure under normal gravity with a forced air flow parallel to its surface is presented.
Abstract: A numerical study of leading edge anchoring characteristics of diffusion flames established over a liquid ethanol film in a confined environment at atmospheric pressure under normal gravity with a forced air flow parallel to its surface is presented. A numerical model, which solves the transient, two-dimensional, gas-phase governing conservation equations with proper interface coupling conditions, is employed. The model uses a global single-step reaction for ethanol–air oxidation to model the finite rate chemical kinetics and an optically thin radiation model to account for thermal radiation losses by absorbing species in a nonluminous flame. Validation of the numerical model is carried out against the available experimental data in terms of temperature profiles. The effect of free stream air velocity on the fuel mass burning rate and the movement of the flame anchoring point is further investigated. The emphasis is on investigating flame anchoring point, located upstream of the leading edge at low air ve...
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01 Jan 1986
TL;DR: In this paper, a theoretical model of a laminar diffusion flame at the leading edge of a fuel plate in a forced convective flow is presented and solved numerically to study the flame stabilization and blowoff phenomena.
Abstract: Abstract A theoretical model of a laminar diffusion flame at the leading edge of a fuel plate in a forced convective flow is presented and solved numerically to study the flame stabilization and blowoff phenomena. The system of governing equations consists of the two-dimensional Navier-Stokes momentum, energy and species equations with a one-step overall chemical reaction and second-order, finite rate Arrhenius kinetics. The computation is performed over a wide range of Damkohler numbers. For large Damkohler numbers, envelope flames are found to exist where the computed fuel evaporation rate, the flame stand-off distance and the velocity profiles show certain similitude. As the Damkohler number is lowered, a transition to open-tip flame takes place where the flame becomes stabilized on the sides of the fuel plate. Further decreasing of the Damkohler number pushes the diffusion flame downstream out of the leading edge region. In this paper, the flame structures of the envelope and the open-tip flames are p...
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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
"A Numerical Study of Leading Edge A..." refers background in this paper
...Subsequent to the earlier studies, T’ien (1986) included the effect of radiative heat loss from the condensed fuel surface in a theoretical analysis of diffusion flame extinction....
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...Chen and T’ien (1986) solved the two-dimensional Navier–Stokes equations including the energy and species conservation equations to study the flame stabilization and blow-off phenomena over a vertically oriented condensed fuel surface placed in a forced convective flow field....
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TL;DR: In this paper, an analysis is developed for predicting extinction of the diffusion flame that is established when an oxidizing gas flows about the nose of a vaporizing fuel body, using the limit of a large ratio of the activation energy to the thermal energy at the flame for the overall combustion process.
105 citations
"A Numerical Study of Leading Edge A..." refers background in this paper
...Spalding (1954) was one of the earliest investigators to present a theory on extinction of diffusion flames based on finite rate Arrhenius-type chemical kinetics....
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...Krishnamurthy et al. (1976) investigated the gas phase extinction at the nose of a vaporizing fuel body....
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TL;DR: In this article, flat diffusion flames were probed and extinguished adjacent to surfaces of poly(methyl methacrylate) and liquid methyl metha-rylate, and the results revealed structural differences attributable to differing thermal properties of the fuels.
Abstract: Since poly(methyl methacrylate) is known to depolymerize largely to its monomer when heated, the chemical kinetics in the gaseous diffusion flame produced by this polymer in a fire may coincide with that of burning liquid methyl methacrylate. To test this hypothesis, flat diffusion flames were probed and extinguished adjacent to surfaces of each of these fuels. Profiles of temperature and of concentrations of stable chemical species are reported, as are gas velocities of approach flow required to produce extinction for various oxygen/nitrogen ratios of the stream. Results revealed structural differences attributable to differing thermal properties of the fuels. Many fuel species were observed in the gas phase, their profiles being partially rationalized on the basis of a suggested decomposition mechanism for gaseous methyl methacrylate. Overall kinetic parameters for gasphase combustion, obtained by use of extinction results in a previously developed theory, are nearly the same for the polymer and monomer but appear to differ by amounts exceeding experimental uncertainties. It is suggested that this may be traced to small differences in fuel species leaving the condensed phase which, for the polymer, is covered by a thin, two-phase region.
81 citations
"A Numerical Study of Leading Edge A..." refers background in this paper
...Seshadri and Williams (1978) conducted extensive experiments on the structure and extinction of diffusion flames above condensed fuels in counterflow configurations....
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TL;DR: In this article, a theoretical model of a laminar diffusion flame at the leading edge of a fuel plate in a forced convective flow is presented and solved numerically to study the flame stabilization and blowoff phenomena.
Abstract: A theoretical model of a laminar diffusion flame at the leading edge of a fuel plate in a forced convective flow is presented and solved numerically to study the flame stabilization and blowoff phenomena. The system of governing equations consists of the two-dimensional Navier-Stokes momentum, energy and species equations with a one-step overall chemical reaction and second-order, finite rate Arrhenius kinetics. The computation is performed over a wide range of Damkohler numbers. For large Damkohler numbers, envelope flames are found to exist where the computed fuel evaporation rate, the flame stand-off distance and the velocity profiles show certain similitude. As the Damkohler number is lowered, a transition to open-tip flame takes place where the flame becomes stabilized on the sides of the fuel plate. Further decreasing of the Damkohler number pushes the diffusion flame downstream out of the leading edge region. In this paper, the flame structures of the envelope and the open-tip flames are p...
72 citations
01 Jan 1975
TL;DR: In this article, the gas velocity and temperature profiles across the laminar boundary layer with a diffusion flame over methanol or ethanol were measured with the free stream, of air parallel to the liquid-fuel surface.
Abstract: The gas velocity and temperature profiles across the laminar boundary layer with a diffusion flame estblished over methanol or ethanol were measured with the free stream, of air parallel to the liquid-fuel surface. The flame stabilizing mechanism and fuel consumption rate are discussed. The results show that the maximum velocity appearing near the blue-flame zone, where the gas stream is accelerated, increases downstream and exceeds the free-stream velocity at a point about 0.2 cm from the leading edge of the fuel vessel. The temperature at the blue-flame zone is found to increase downstream about 1.5 cm from the leading edge of the fuel vessel and then to decrease slightly still farther downstream. The fuel consumption rate is observed to increase monotonically with the increase of the free-stream velocity. It is shown that in order to elucidate the flame stabilizing mechanism, the velocity profile change due to the flame reaction must be taken into account. The diffusion flame over the liquid fuel can be considered to remain stable until the leading flame edge shifts beyond the leading edge of the fuel vessel due to the increase of the free stream velocity.
63 citations