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

The trappingandtransport of sootaggregatesbetween a burningsuspendeddroplet and its  ame in a convectionfree (microgravity) environment are discussed. Many researchers have utilized the suspended droplet method for studyingdroplet combustion in microgravitywhere the intent is to create a spherically symmetric burning process. In the ideal case, soot particles are trapped in a spherical shell-like structure between the droplet and the  ame. Results presented show that the Ž ber support can prevent the formationof spherical soot shells if the Ž ber diameter is large relative to the droplet diameter are presented for suspended droplets burning in microgravity. The effect of the Ž ber is conjectured to arise by its in uence on the gas-phase temperature and Stefan velocity Ž elds around the burning droplet. Droplets with initial diameters between 700 and 850 μm were mounted on silica quartz Ž bers with diameters of 57, 110, 220, and 330 μm, and the droplets were ignited with sparks generated from two retractable electrode pairs. Photographic records of the burning process show soot aggregates inside the  ame forming a shell-like structure, which evolves into a nonsymmetric conŽ gurationdue to a nonsymmetricdistribution of thermophoretic and Stefan drag forces around the droplet caused by  ame/Ž ber interactions. For the four Ž 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 Ž ber diameter increases.