A 3D Numerical Study on Opposed Flow Flame-Spread over Thin Parallel Fuel Sheets of Finite Widths in Microgravity
01 Jan 2017-pp 551-558
TL;DR: In this article, a model of flame spread over an array of fuel sheets of finite width size has been modeled and numerically investigated for opposed, low convective flows in microgravity, and steady flame spread rates were observed for all separation distances up to the separation distance of flame extinction.
Abstract: Flame spread over an array of fuel sheets of finite width size has been modeled and numerically investigated for opposed, low convective flows in microgravity. As opposed to the previous studies based on 2D models, steady flame spread rates were observed for all separation distances up to the separation distance of flame extinction. The flame spread rate increased with decrease in separation distance up to a point where it was maximum, further reduction in separation distance, reduced the flame spread rate. The flammability map as a function of separation distance was also obtained for different fuel widths. While the extinction map qualitatively matches with the flammability map obtained from the 2D model, the flame extinguished at higher oxygen levels with the decrease in fuel width due to radiation heat losses.
References
More filters
TL;DR: In this paper, a flame spread model is formulated in three dimensions to simulate opposed flow flame spread over thin solid fuels, coupled with a three-dimensional gas radiation model to assess the role of radiation and effect of dimensionality on the prediction of the flame spread phenomena.
Abstract: In this work a flame-spread model is formulated in three dimensions to simulate opposed flow flame spread over thin solid fuels. The flame-spread model is coupled to a three-dimensional gas radiation model. The experiments [1] on downward spread and zero gravity quiescent spread over finite width thin fuel are simulated by flame-spread models in both two and three dimensions to assess the role of radiation and effect of dimensionality on the prediction of the flame-spread phenomena. It is observed that while radiation plays only a minor role in normal gravity downward spread, in zero gravity quiescent spread surface radiation loss holds the key to correct prediction of low oxygen flame spread rate and quenching limit. The present three-dimensional simulations show that even in zero gravity gas radiation affects flame spread rate only moderately (as much as 20% at 100% oxygen) as the heat feedback effect exceeds the radiation loss effect only moderately. However, the two-dimensional model with the gas radi...
35 citations
01 Jan 1979
TL;DR: In this paper, the authors concenred with the steady, two-dimensional vertical downward spread of flame along two parallel sheets of paper placed in air, and correlated experimentally the flame spread rate, the distance separating, the two sheets and the width of the paper.
Abstract: This paper is concenred with the steady, two-dimensional vertical downward spread of flame along two parallel sheets of paper placed in air. The purpose of the present study is to correlate experimentally the flame spread rate, the distance separating, the two sheets and the width of the paper, and to model theoretically the flame spread in the presence of interaction of multiple flames. The flame spread rate depends more on the separation distance between the two sheets of paper than on the width of the paper. Within the narrow space region, C≤0.3 cm, the flame spread rate is reduced to about a half of that for burning of a single sheet of paper. On the other hand, in the wider space region, C≥0.5 cm, the flame spread rate increases and becomes greater than that of a single sheet. It reaches the maximum value at a finite separation distance, C=1.5∼2.0 cm. A simple theoretical model was used to explain the experimental results. The theoretical flame spread rates predicted from the model were found to be in good agreement with the experimental data. It is concluded from the experimental and theoretical results that in the narrow space region between the burning sheets of paper the convective heat transfer predominates and controls the flame spread rate, whereas in the wider space region the radiative heat transfer from the opposite flame and ember plays an important role in controlling the flame spread rate.
24 citations
TL;DR: In this article, a model for the analysis of heat transfer to the unburned paper is employed to predict the flame spread rate in the presence of multiple flames in the air.
Abstract: This paper is concerned with the steady, two-dimensional vertical downward spread of flame along several, parallel sheets of paper in air. The flame spread regime is divided into the following classes according to the separation distance. In the wider space region, C ≥ 5 mm, the flame spread rate is greater than a single sheet of paper and passes through a maximum value at a finite separation distance. It also increases with the number of sheets and approaches asymptotically a constant value. A simple model for the analysis of heat transfer to the unburned paper is employed to predict the flame spread rate in the presence of multiple flames. On the other hand, within the narrow space region, C ≤ 3 mm, the flame is unable to spread vertically downward over three parallel sheets of paper because no flame can exist in the narrow space between sheets of paper.
23 citations
TL;DR: In this paper, a steady, two-dimensional flame-spread model with flame radiation was employed and adapted in this work and some of the features were presented, including flow channelling effect and flame radiation interactions.
Abstract: Flame spread in an array of thin solids in low-speed concurrent flows was investigated and numerical solved. A previous steady, two-dimensional flame-spread model with flame radiation was employed and adapted in this work. The flame structures of spreading flames between parallel solids were demonstrated and some of the features were presented, including flow channelling effect and flame radiation interactions. The channelling effect is caused by flow confinement by the presence of the other solids; the flows through the hot combustion gases are accelerated downstream drastically. Radiation interactions between flames and solids contributed to a less heat-loss system, and radiation re-absorption by flames resulted in a larger flame with higher temperature, which increased the conductive heat fluxes to the solids and flame spread rate. Consequently, the extinction limit for the interacting flames is extended beyond the low-speed quenching limit for a single flame. The influence of the separation distance o...
17 citations
TL;DR: In this paper, a numerical study has been carried out to gain physical insight into the phenomena of opposed flow flame spread over an array of thin solid fuel sheets in a microgravity environment.
Abstract: In this work a numerical study has been carried out to gain physical insight into the phenomena of opposed flow flame spread over an array of thin solid fuel sheets in a microgravity environment. The two-dimensional (2D) simulations show that the flame spread rates for the multiple-fuel configuration are higher than those for the flame spreading over a single fuel sheet. This is due to reduced radiation losses from the flame and increased heat feedback to the solid fuel. The flame spread rate exhibits a non-monotonic variation with decrease in the interspace distance between the fuel sheets. Higher radiation heat feedback primarily as gas/flame radiation was found to be responsible for the increase in the flame spread rate with the reduction of the interspace distance. It was noted that as the interspace distance between the fuel sheets was reduced below a certain value, no steady solution could be obtained. However, at very small interspace distances, steady state spread rates were obtained. Here, due to...
13 citations