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

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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.