Section B Fire and Explosion - Extinguishment Characteristics of a Jet Diffusion Flame with Inert-Gas Vortex Ring

Abstract

For firefighting, we propose a Jet Diffusion Flame…?>the vortex-ring transport method using a gaseous fire-extinguishing agent. The vortex ring formed with a gaseous extinguishing agent has a possibility to transport the extinguishing gas more effectively and over longer distance than jet flows which issue from conventional extinguishers. To clarify the extinguishing characteristics of the inert-gas vortex ring, blowout experiments using a methane-air jet diffusion flame have been performed. Nitrogen, carbon dioxide, argon, and air are used for forming a vortex ring with a round orifice. The extinguishing velocity limit has been measured. The extinguishing velocity limit is defined as the lowest displacement velocity of the vortex ring which can blow the jet diffusion flame off perfectly. From the experimental results, it is found that all inert-gas vortex rings indicate the lower extinguishing velocity limit than the air vortex ring. This means that the inert-gas vortex ring can travel in air while keeping its extinguishing ability. All inert-gas vortex rings retain extinguishing effectiveness over a distance longer than seven times that of the orifice diameter. Significantly, after a distance larger than four times the orifice diameter, the extinguishing velocity limits of all inert gases show constant values independent of the traveling distance of the vortex ring. Furthermore, the order of the extinguishing effectiveness of the inert-gas vortex ring is CO₂ > Ar > N₂. This result is different from the extinguishing effectiveness ranking determined by a cup-burner method, and it is considered that the extinguishing effectiveness ranking is influenced by the transport process of the inert gas to the flame. When the extinguishing velocity limit is scaled by the Peclet number which is defined as the ratio between displacement velocity of vortex ring at extinguishment limit and mass diffusion rate of inert gas, the data of the Peclet number can be expressed as a single curve as a function of the normalized traveled distance of the vortex ring.