Flame quenching performance of ceramic foams

Quenching of gaseous hydrocarbon-air and hydrocarbon-oxygen flames in porous media has been investigated. Experiments were conducted in a vertical Plexiglas flame tube and in a horizontal steel tube. The flammable mixture is ignited by a spark and failure or successful transmission of the flame through the porous media was determined by visual observation. Ceramic foams of different porosities and ceramic spherical beads were tested in both apparatus. The quenching composition limits were determined as a function of effective channel diameter of the porous media. The Peclet number for the quenching limit mixtures were calculated in order to gain some insight into the mechanism of flame extinction. The results have direct application to the design of flame arresters using ceramic foams and spherical beads as flame arresting elements.; The flame quenching limits are found to be dependent on the characteristic length scale that describes the effective channel diameter of the porous media. It is found that the ceramic foam is slightly less effective than the spherical beads in quenching flames and much less effective than using straight channels with the same diameter. Analysis of the experimental results show there is a large disparity of the calculated Peclet number from the value predicted by the thermal quenching theory. While the thermal theory of heat loss is an important mechanism responsible for flame quenching, the analysis indicates that the preferential diffusion and flame stretch may play a role in the flame quenching process. In particular, for the rich limits there is evidence of flame stretch effects for the tests done in the horizontal closed-ignition end tube.