Sootshell formation in microgravity droplet combustion

The formation of the sootshell in microgravity droplet combustion can influence many aspects of droplet burning. Soot formation is believed to influence the burning rate through (1) changes in thermophysical properties since sootshell serves asa heat sink, (2) physical barrier effects as sootshell can reduce fuel mass flux, and (3) through reduction in the effective heat of combustion. In an effort to better understand the mechanism leading to sootshell formation, experiments were performed in the NASA 2.2 See droptower and JAMIC 10 See dropshaft. In these experiments, rapid insertion of a blunt plunger was used to blowoff the symmetric sootshell formed after the quasi- steady period. This allowed for the disruption of the original sootshell allowing for the observation of the re-formation of a new sootshell, from initiation near the flame followed by transport towards the equilibrium location. The measured sootshell velocity ( with nearly constant magnitude at the various radial position), which can be used to infer thermophoretic velocity, are similar in magnitude to the velocities of carbon particles measured in environments of imposed linear temperature profiles under microgravity conditions. These observations are in contrast to the recent modeling results that suggest photophoretic transport as an important mechanism in the transport of soot agglomerates