Time-resolved size, velocity, and temperature statistics of aluminum combustion in solid rocket propellants

Abstract

The study of time-resolved aluminum combustion mechanisms is essential for understanding the deflagration of ammonium perchlorate-based metalized solid rocket propellants. In order to gain further insight into the performance of solid propellants, spatially and temporally resolved aluminum agglomerate particle dynamics are obtained by combining digital in-line holography (DIH) and two-color imaging pyrometry with high-speed acquisition at up to 20 kHz. Holography is used to find the size, three-dimensional position, and three-dimensional velocity evolution of agglomerates over time. Then, the temperature of individual particles is extracted from the high-speed imaging pyrometry. This diagnostic technique not only produces joint size, position, velocity, and temperature statistics over time, but also captures the combustion histories for thousands of particles per experiment. For the first time, these spatial and temporal dynamics of individual aluminum particulates are examined while they travel away from the propellant surface. Initial results demonstrate how aluminum agglomerates of similar size exhibit varying initial acceleration but similar steady-state velocities. Average velocity also decreases as particle size increases, which is consistent with viscous flow dynamics of small particles in convective flow. As they move further away from the propellant surface, large agglomerates also show a convergence to an average projected temperature between the melting point of aluminum oxide and the boiling point of aluminum. The average projected particle surface temperatures were measured to be 2494 ± 231 K. The method outlined in this work demonstrates a new capability for gathering the evolution of joint statistics for aluminum agglomerates in solid-rocket propellants. Future applications of this technique can be used to evaluate the detailed combustion mechanisms of existing or new propellant formulations.