Extinction of Jet Diffusion Flames by Water Mist

Abstract

In the present study, effect of water mist on the stabilizing and extinction mechanisms of a jet diffusion flames developing in a coaxial-flow burner was investigated experimentally, using propane as fuel. Water mists were generated by a commercial ultrasonic humidifier (Toyotomi-TUH-A9). The characteristics of water mist were measured by a PDPA. The mist sizes were found to have nearly normal distribution and ranged from 1 to 44 μm. The arithmetic and the Sauter mean diameters are D₁₀ ≒ 15 μm, D₃₂ ≒ 21 μm, respectively. When water mist was added into air flow, the flame stability limits and the distributions of flame temperatures, soot concentrations, flame brightness were measured. As a result, it was shown that the flame stability limits and flame temperatures are reduced as the water mist flow rates are increased because of the extinguishment due to evaporation which causes the cooling and depletion of oxygen in the flame zone. Likewise, soot concentrations and the flame brightness decrease with the increase of the mist flow rates. Furthermore, it was shown that extinction of the attached flame was caused by increase of the heat transfer from flame to mist. On the other hand, it was found that the local extinction of turbulent flame was spread with the increase of the water mist flow rates. Also it was confirmed that the structure of the turbulent diffusion flame varied with the mist flow rates which flowed into in a turbulent flame.