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. (c) 2020 The Combustion Institute. Published by Elsevier Inc. All rights reserved.

Aluminum particle combustion is a critical component in solid propellant operation. Understanding these processes is essential for improving specific impulse and other performance metrics. Prior studies of aluminum particle combustion in the literature have focused on spatial and temperature statistics for a single propellant strand size, which is typically significantly smaller than the full grain size used in aerospace and defense applications. In this work, we aim to determine the effect of increasing propellant strand size on several key properties of aluminum particle combustion at atmospheric pressure. To accomplish this, we use simultaneous high speed holography and imaging pyrometry to obtain temporally resolved spatial and temperature information. Here, we discuss how agglomerate size, velocity, and temperature statistics vary as a function of propellant strand size from 6 mm up to 19 mm in diameter. By understanding how the statistics scale as a function of strand size, we can determine how to extrapolate lab-scale experimental data to full-scale propellant burns.

Holography is a powerful tool for three-dimensional imaging. However, in explosive, supersonic, hypersonic, cavitating, or ionizing environments, shock-waves and density gradients impart phase distortions that obscure objects in the field-of-view. Capturing time-resolved information in these environments also requires ultra-high-speed acquisition. To reduce phase distortions and increase imaging rates, we introduce an ultra-high-speed phase conjugate digital in-line holography (PCDIH) technique. In this concept, a coherent beam passes through the shock-wave distortion, reflects off a phase conjugate mirror, and propagates back through the shock-wave, thereby minimizing imaging distortions from phase delays. By implementing the method using a pulse-burst laser setup at up to 5 million-frames-per-second, time-resolved holograms of ultra-fast events are now possible. This technique is applied for holographic imaging through laser-spark plasma-generated shock-waves and to enable three-dimensional tracking of explosively generated hypersonic fragments. Simulations further advance our understanding of physical processes and experiments demonstrate ultra-high-speed PCDIH techniques for capturing dynamics.

Laser diagnostics are essential for time-resolved studies of solid rocket propellant combustion and small explosive detonations. Digital in-line holography (DIH) is a powerful tool for three-dimensional particle tracking in multiphase flows. By combining DIH with complementary diagnostics, particle temperatures and soot/smoke properties can be identified.

Combustion of aluminum droplets in solid rocket propellants is studied using laser diagnostic techniques. The time-resolved droplet velocity, temperature, and size are measured using high speed digital in-line holography and imaging pyrometry at 20 kHz.