Combustion of solid material under microgravity -In case of porous material-

重力场引起的自然对流使燃烧现象复杂化。由于固体燃烧是由许多物理过程组成的，微重力场通过消除自然对流对固体燃烧过程的研究是很有帮助的，在本项目的第一年，我们采用了三种落塔（5m、50m和500m落塔）发展了微重力实验技术。成功地测量了棉线和纸张的火焰传播速度，并在第二年研究了氧气浓度、试样尺寸等参数对火焰传播速度的影响。所需氧气量越少，传播速度越高。氧浓度越高，传播速度越快。模拟多孔材料的纸张基质也进行了燃烧，以检查材料内部的孔径大小、通风可用性和氧气浓度的影响。在微重力条件下，除氧浓度外，其他参数对火焰传播速度影响不大，而在正常重力条件下，这些参数对火焰传播速度影响较大。这是因为这些参数是通过改变材料内部的自然对流强度来影响燃烧的。在最后一年中，我们研究了由单一化学成分制成的聚苯乙烯泡沫珠的燃烧，以找出多孔材料燃烧的主导因素。结果表明，固体材料的火焰传播现象主要受未燃区供热率和燃烧区供氧率的控制。在微重力条件下，当热供应占主导地位时，火焰传播更容易，因为热量不会被自然对流带走。当后一因素占主导地位时，火焰传播在正常重力下借助自然对流来供应氧气更快。

Natural convection caused by gravity field makes the combustion phenomena complicated. Since solid combustion is constituted by many physical processes, microgravity field is quite helpful to study its combustion processes through the elimination of natural convection.In the first year of this project microgravity experimental technique have been developed by using three types of drop tower, 5m, 50m and 500m drop towers. The flame propagation speed of cotton strings and paper sheet has been successfully measured.In the second year, the effect of various parameters, such as oxygen concentration, and dimension of test pieces have been investigated. The smaller amount of required oxygen, the higher propagation velocity. The higher oxygen concentration also gave the higher propagation velocity. The matrix of paper sheet, simulation of porous material, has also burned to examined the effect of pore size inside of the material, ventilation availability and oxygen concentration. Under microgravity these parameters except oxygen concentration did not affect to the flame propagation speed while they had strong effect under normal gravity. This is because these parameters have effect on the combustion through the change of natural convection strength inside the material.In the final year, the combustion of polystirene foam beads, which is made from a single chemical component have been investigated to hnow the dominant factors of porous material combustion. The results showed that flame spread phenomena of solid material is mainly dominated by the rates of heat supply to the unburned region and oxygen supply to combustion region. When the former factor, heat supply, is more dominant flame propagation is easier under microgravity because heat is not taken away by natural convection. When the later factor is dominant, flame propagation is faster under normal gravity with aid of natural convection to supply oxygen.