Experimental Study on Radiative Ignition of Filter Paper with Near Infrared Radiation Under Microgravity

Experiments with radiative ignition were performed in microgravity to elucidate the events arising during the ignition process in a quiescent field. Filter paper was irradiated by Diode laser light (800.1 nm), which is little absorbed in the gas phase, at various oxygen concentrations (0-50%). The ignition delay was measured for various experimental conditions. The density changes of the gas phase before ignition was observed in detail by a Mach-Zehnder interferometer. The results showed that heat conduction from the sample surface induced a weak chemical reaction in the vicinity of the sample surface, and this propagated outward to achieve combustion. The ignition delay decreased with increases in O_2 concentration because the mixture near the sample surface contained more oxygen causing an immediate transition from the weak chemical reactions to the strong reactions of the combustion.