Abstract
An experimental study of radiative ignition of sheet paper has been performed in microgravity to determine the events occurring in ignition processes in a quiescent field. Experiments were conducted on filter paper using a CO2 laser with a mean incident flux of about 5.8 W/cm2 in various oxygen concentrations (0%–35%) and at various pressures (0.5–2 atm). The laser beam was irradiated perpendicular to the sample surface. The ignition delay was measured for various experimental conditions with high-speed video images or Hi-8 video images taken in microgravity. The gas-phase and solid-surface temperature changes were observed by a Mach-Zehnder interferometer and an infrared camera. The results showed that the ignition delay became shorter with increases in oxygen concentration, and it was observed that the gas-phase temperature increased more than that of the solid surface. Further, the increase in gas-phase temperature was larger with oxygen than without oxygen, though there were increases in the gas-phase temperature even without oxygen. The results showed that chemical processes, such as gas-phase reactions, are essential in the ignition mechanism, as are physical processes, such as heating the solid material, and gas-phase laser absorption. The research clearly showed the importance of each process by utilizing a non-convective flow field where gravitational forces were not acting.
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