The effect of diluent type in atmosphere on flame spread over thermally thin combustibles in microgravity

The effects of diluent type on flame spread over thermally thin combustibles for different diluents in atmospheres have been bivestigated computationally. The re-absorption effect is incorporated in the problem by solving the Radiative Transfer Equation ( RTE). The calculated results show that the diluent type in atmosphere has significant effect on the flame spread. For N(2) diluent, the radiation re-absorption in combustion zone and the surrounding atmosphere has little effect on the flame spread rate and the flame structure, thus the flame can be treated as optically thin flame, and the re-absorption can be neglected in the analysis. In this cam, at low flow velocity the radiation cooling effect becomes significant and manifests in lowered flame spread rate and flame temperature. In contrast, for CO(2) diluent the re-absorption of radiation has strong effect on the flame structure and flame spread rate. Due to re-absorption, the surrounding atmosphere near the flame will absorb the thermal radiation emitted from the combustion zone. Under such conditions the conductive and radiative heat transfer from flame to fuel surface is enhanced, the radiative heat transfer plays almost equally important role in flame spread mechanism, and the flame spread rate reaches its maximum value in quiescent microgravity. With the increase of the opposed flow velocity, the heated layer around the flame is removed, and the effect of the radiation re-absorption declines, and the flame spread rate decreases monotonically