A series of experiments were conducted in the 3.6-s microgravity drop tower and normal gravity to investigate the effect of solid fuel curvature, conduction, and reradiation on the flame extinction of spherical polymethyl methacrylate (PMMA). In the semi-quiescent microgravity environment, flame extinction was observed if the PMMA diameter was larger than 40 mm, because of a smaller flame conductive heating in larger diameter (i.e., the curvature effect). Compared to the droplet combustion with a low evaporation point and fast heat convection in the liquid phase, the solid fuel has a high pyrolysis point and large transient heat conduction. Thus, the large surface reradiation effectively cools down the fuel surface to promote extinction. Also, as the initial burning duration increases, the conductive cooling into the solid fuel decreases, which delays or prevents the flame extinction in microgravity. The extinction criterion for microgravity flame is explained by the critical mass flux and mass-transfer number. This work helps to understand the curvature effect of solid fuel on flame extinction and the material fire safety in the microgravity spacecraft environment.

在3.6 s微重力下降塔和法向重力下进行了一系列实验，以研究固体燃料曲率，传导和再辐射对球形聚甲基丙烯酸甲酯（PMMA）的火焰熄灭的影响。在半静态微重力环境中，如果PMMA直径大于40 mm，则会观察到火焰熄灭，这是因为较大直径的火焰传导加热较小（即曲率效应）。与具有低蒸发点和液相快速对流的液滴燃烧相比，固体燃料具有较高的热解点和较大的瞬态热传导。因此，大的表面辐射有效地冷却了燃料表面，从而促进了熄灭。而且，随着初始燃烧持续时间的增加，进入固体燃料的传导性冷却也会降低，在微重力作用下延迟或阻止了火焰的熄灭。微重力火焰的熄灭标准由临界质量通量和传质数解释。这项工作有助于了解固体燃料对熄灭的曲率影响以及在微重力飞船环境中的材料防火安全性。