<title>Simultaneous measurements of soot formation and hydroxyl concentration in various oxidizer diffusion flames</title>

Abstract

This research work studied the effects of oxidant constitution on soot formation in diffusion flames by simultaneously measuring the soot properties and the species concentration. The soot properties are measured by the laser light scattering and extinction method and the hydroxyl concentration is measured by the laser-saturated fluorescence (LSF) method. The temperature distributions in the flames were measured by the two-line LSF technique and by fine wire thermocouple. . The hydroxyl fluorescence profiles for all four flames presented here show that the OH fluorescence intensities peak near the flame front. The OH fluorescence intensity drops sharply towards the dark region of the flame and continues declining to the sooting region. The OH fluorescence profiles also indicate that OH fluorescence decreases with increasing height in the flames for all flames investigated. Varying the oxidizer composition resulted in corresponding variation in the maximum OH concentration and flame temperature. Furthermore, it appears that the maximum OH concentration for each flame increases with increasing flame temperature. Soot particles are formed on the fuel side of the flame front where the number density is high for all four flames. The fuel/oxygen/argon flame (Flame C) shows the largest soot particle size, and shortest flame height. In the higher portion of the Flame C, the soot volume fraction was observed to decrease indicating that soot is being oxidized before leave the flame. The fuel/oxygen/carbon dioxide flame (Flame B) shows the least soot formation in the flame. The experiment demonstrated that soot formation can be reduced by changing the inert of the oxidant while keeping the fuel flow rate and oxygen flow rate constant. The carbon dioxide dramatically reduced the soot formation in the flames. The temperature effect may play the major role in this reduction. Some researchers have doubted that the hydroxyl radical is the dominant oxidizer of the soot particles in flames. In this investigation, both calculation and measurement data show that the highest OH concentration flame has the most soot formation inside the flame.