Measurements of Soot and Model Assessment for Energetic Material Intermediaries at Fireball-Relevant Conditions

Soot is a by-product formed from the incomplete combustion of hydrocarbon-based fuels. As a result, the detonation of common highly explosive (HE) compounds produces some level of soot particulate. These particulates are of interest due to their effect on the formation of the resultant fireball via changes in fluid dynamics and internal radiative heating. In the case of a fireball initiated by a nuclear event, soot particles can act as nucleation sites for radionuclides through absorption and adsorption. Soot particles also contribute to the fallout in the form of a propagating ash cloud or by acting as sites for water or ice condensation, producing additional cloud cover and precipitation that may spread radioactive material more readily. These aspects make soot an important target to track in the case of long-term fallout analysis. However, predictive uncertainties related to particle size distributions, inception, growth, and chemical composition can make fallout modeling difficult, especially at fireball conditions. In this work, high-temperature experiments were conducted using shock tube and laser absorption to measure soot time-histories, volume fraction, and induction times for fireball intermediates. A comparative baseline is established between a Lawrence Livermore National Laboratory mechanism developed for n-C12 and i-C12 fuels and a University of Central Florida mechanism initially created for studying soot production from biofuels. The current research provides insights into the deficiencies of nuclear fallout models.