Opposed flow flame spread over an array of thin solid fuel sheets in a microgravity environment

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 oxygen starvation the flame spread rate decreased and eventually at some interspace distance the flame extinguished. With fuel emittance (equal to absorptance) reduced to ‘0’ the flame spread rate was nearly independent of the interspace distance, except at very small distances where the flame spread rate dropped due to oxygen starvation. A flame extinction plot with the extinction oxygen level was constructed for the multiple-fuel configuration at various interspace distances. The default fuel with an emittance of 0.92 was found to be more flammable in the multiple-fuel configuration than in a single fuel sheet configuration. For a fuel emittance equal to zero, the extinction oxygen limit decreases for both the single and the multiple fuel sheet configurations. However, the two flammability curves cross over at a certain fuel separation distance. The multiple-fuel configurations become less flammable compared to the single fuel sheet configuration below a certain separation distance.