Soot Patterns Around Suspended n-Heptane Droplet Flames in a Convection-Free Environment

Abstract

Thetrappingandtransportofsootaggregatesbetweenaburningsuspendeddropletanditse ameinaconvectionfree (microgravity ) environment are discussed. Many researchers have utilized the suspended droplet method for studying droplet combustion in microgravity where the intentis to createa spherically symmetric burning process. In the ideal case, soot particles are trapped in a spherical shell-like structure between the droplet and the e ame. Resultspresented showthatthee bersupport canpreventtheformation of spherical sootshellsifthee berdiameter is large relative to the droplet diameter are presented for suspended droplets burning in microgravity. The effect of the e ber is conjectured to arise by its ine uence on the gas-phase temperature and Stefan velocity e elds around the burning droplet. Droplets with initial diameters between 700 and 850 µm were mounted on silica quartz e bers with diameters of 57, 110, 220, and 330 µm, and the droplets were ignited with sparks generated from two retractable electrodepairs. Photographic records of the burning process show soot aggregatesinside the e ame forming ashell-likestructure, whichevolvesinto anonsymmetriccone guration dueto anonsymmetricdistribution of thermophoretic and Stefan drag forces around the droplet caused by e ame/e ber interactions. For the four e ber diameters examined, the burning rates (extracted over a large portion of burning process )appear to approach the free droplet value as the ratio of the initial droplet diameter to the e ber diameter increases.