A Numerical Study of Flame Spread Over Thin Cellulosic Fuels in Microgravity PDF Download
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Author: Yang Long
Publisher:
ISBN:
Category : Cellulose
Languages : en
Pages : 348
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Author: Yang Long
Publisher:
ISBN:
Category : Cellulose
Languages : en
Pages : 348
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Author: Ama R. Carney
Publisher:
ISBN:
Category : Aerospace engineering
Languages : en
Pages : 125
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Book Description
Microgravity experiments are performed to study wind-assisted flame spread over discrete fuel elements. Ultra-thin cellulose-based fuel segments are distributed uniformly in a low-speed flow and flame spread is initiated by igniting the most upstream fuel segment. Similar to continuous fuels, flame spread over discrete fuels is a continual process of ignition. Flame propagation across a gap only occurs when a burning fuel segment, before it burns out, ignites the subsequent segment. During this process, gaps between samples reduce the fuel load, increasing the apparent flame spread rate and decreasing the heat transfer between adjacent segments. The reduction in heat transfer decreases the solid burning rate. In this study, sample segment length, gap size, and imposed flow velocity are varied to study the impacts on burning characteristics, including propensity of flame spread, flame spread rate, and solid burning rate. Detailed profiles of the transient flame spread process are also presented.
Author: Takashi Kashiwagi
Publisher:
ISBN:
Category :
Languages : en
Pages : 4
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Author: Jeanhyuk Park
Publisher:
ISBN:
Category : Flame spread
Languages : en
Pages : 131
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Book Description
Building fire, Forrest fire, and warehouse compartment fire are some of the most frequently occurring practical fire hazards in modern world. Although these types of hazards seem irrelevant from one another, they have some things in common from the perspective of fire protection engineering, in that they all have a very similar fundamental fuel-gap configuration, or discrete fuel configuration. There has been some studies in the past regarding the subject, yet it is not the most popular in the field. Furthermore, there is even fewer, if not any, numerical analysis done to fires in discrete fuel configuration. Discrete fuel arrangements represent some practical fire hazard situations, such as compartment fires in enclosed vehicles. In this study, an unsteady two-dimensional numerical model (Fire Dynamics Simulator) was used to simulate concurrent flame spreadover paper-like thin solid fuels in discrete configurations in microgravity (0g, where a20cm/s flow is imposed) and in normal gravity (1g). An array of ten 1cm-long fuel segments is uniformly distributed in the flow direction (0g) or in the vertical direction (1g).A hot spot ignition source is applied at the upstream leading edge of the first fuel seg-ment. The separation distance between the fuel segments is a parameter in this study, ranging from 0 (corresponding to a continuous fuel) to 3cm. Using this setup, the spread rate of the flame base and the fuel burning rate were studied. The spread rate in 1g and 0g increases with increasing separation distance. This is due to the gaps in the discrete fuel that force the flame base to jump to the subsequent fuel segment when the upstream segment burns out. On the other hand, the fuel burning rate behaves differently in 1g versus 0g. At a flow velocity of 20 cm/s in 0g, the flame reaches a limiting length and the flame length is approximately the same ( 4cm) for all fuel configurations. Therefore, as the separation distance increases, the preheating length (the fuel area exposed to the flame) decreases, resulting in a smaller burning rate. In 1g, the buoyancy driven flow accelerates as it rises, resulting in a longer flame as the separation distance increases. In all simulated configurations, the flame extends to the last fuel segment before the first fuel segment burns out and the flame spans the entire set of fuel segments. However, flame standoff distance reduces at the gaps between fuel segments, and in some con-figurations, the flame breaks into multiple flamelets. The shorter standoff distance and intense burning at each flamelet base result in a larger total burning rate as the separation distance increases.
Author: Tatsuya Arai
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Author: Stefanus A. Tanaya
Publisher:
ISBN:
Category : Flame spread
Languages : en
Pages : 432
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Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 62
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The purpose of this thesis is to simulate the downward flame spread over thin fuel (Cellulose and Polymethylmethacrylate) in a natural convection environment. Flame spread over thermally thin fuels in quiescent and opposed-flow environment condition is studied. The study of the flame geometry, size of domain, grid points in x and y directions and boundary conditions are considered. For PMMA fuel comparison of the computational and experimental result for quiescent environment is performed. Effect of fuel half thickness, opposed flow velocity, ambient oxygen concentration and ambient pressure level on the flame spread rate was studied. Comparison of flame spread rate of complete combustion model, equilibrium model and experiments with different half thicknesses for PMMA and cellulose was performed. For cellulose fuel velocity fields and pressure field plots are plotted to understand the flow behavior near the leading edge of the flame. Two dimensional Navier-Stokes equations were implemented in a FORTRAN code which was used for numerical simulation and later on the code is modified. A Matlab code is implemented for plotting the pressure field, temperature field, reaction rate contours, fuel mass fraction and other kind of plots.
Author:
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ISBN:
Category : Electronic books
Languages : en
Pages : 70
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The purpose of this research is to investigate how oxygen concentration, opposed flow velocity and thickness of a thin PMMA fuel affect the flame spread rate and flame extinction in microgravity. The flame spread rate increases with an increase in oxygen concentration. The critical oxygen level, which is the minimum concentration for a flame to spread, is inversely related to the fuel thickness. For fuel thickness above and below a critical thickness, the flame spread rate increases and decreases with a decrease in fuel thickness, respectively. Also, an unexpected extinction is discovered. The critical fuel thickness is inversely related to the opposed flow velocity. The flame spread rate decreases when the opposed flow velocity decreases. Unexpected extinction is discovered when oxygen level is low and opposed flow is absent or weak. The simulation results are consistent with the available experimental results obtained by NASA. For a quiescent environment in microgravity, the critical oxygen level increases with the fuel thickness while the critical oxygen level decreases with the fuel thickness for environments with an opposed flow. The research on how a flame extinguishes reveals that the flame temperature in the anomaly region is lower than the flame temperature in the normal region. A flame extinguishes when the percentage surface radiation loss, which is the ratio of the surface radiation loss to heat generated from combustion, is higher than 45% with an opposed flow and 48% in quiescent environment.
Author:
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ISBN:
Category :
Languages : en
Pages :
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Author:
Publisher:
ISBN:
Category :
Languages : en
Pages :
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