Observation of soot agglomeration process with aid of thermophoretic force in a microgravity jet diffusion flame

Abstract

Soot agglomeration process in a jet diffusion flame was observed under microgravity condition. Laser shadow method was applied to measure the change of soot agglomerates diameter as well as laser attenuation ratio to give a volume fraction of soot in the flame. According to the experimental results, soot agglomerate size became much larger than that in normal gravity flame and its maximums size was more than 100 μm in the flame. Further, the size of the soot agglomerates increased with increase in the distance from the burner exit. To explain the large soot agglomerates formation, the importance of thermophoretic force as well as longer residence time in microgravity was pointed out based on the motion analysis of the individual soot agglomerates determined from the laser shadow method. That is, the soot particle near the flame zone tends to move away from the flame zone because of thermophoretic force and to concentrate at a certain narrow area inside of the flame. This phenomenon in combination with longer residence time in microgravity leads to high concentration of soot particle in a diffusion flame and caused the larger soot agglomerates formation.