An experimental study on particle-cloud flames in a microgravity field

Abstract

Flame propagation experiments were conducted for a PMMA particle cloud in a microgravity field provided by the JAMIC (Japan Microgravity Center), whose microgravity level was 10 −4 –10 −5 g and duration was 10 s. PMMA-polymethyl methacrylate sphere particles with various mass-median diameters from 5.0 to 30.4 μm were dispersed in a flame propagation tube with inner diameter of 38 mm, and then the cloud was ignited 6 s after the release of the drop capsule, because vortex-like motions generated at the time of dispersion stopped after several seconds. The results showed that the maximum flame propagation speed decreased and the equivalence ratio at this point moved to the rich side when the particle size increased. When a very small amount of methane was added to the air, the plots of the flame propagation speed versus the equivalence ratio changed greatly for particles with a mass-median diameter of 8.4 μm, which is different from 5.0-μm particles. It was concluded that for 8.4-μm particles, the flame behavior shifted from a nongaseous type of flame to a gaseous type of flame when a very small amount of methane is mixed with the air. Also, the new arrangement of data, based on the nondimensional distance between particles, verified the change of the flame propagation speed for large-particle clouds. This implies that the flame of a large particle cloud propagates basically according to flame spread between particles.