Thermometry of post detonation fireball environments
Date
2022-12
Authors
LoCurto, Anthony Cecil
Major Professor
Advisor
Michael, James B
Sippel, Travis R
Lu, Meng
Sarkar, Soumik
Ward, Thomas
Committee Member
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Abstract
Metal additives have been shown to improve performance in energetic materials, however, improved thermochemical information within the post-detonation fireball environment is necessary to understand the thermal damage of novel energetic formulations, provide higher fidelity modeling, and predict the defeat of chemical and biological warfare agents. These environments are extremely challenging for diagnostics due to their fast timescales, violent energy release, complex turbulent flow, and high optical densities. Optical diagnostics are well suited for these environments due to their remote sensing capabilities and fast acquisition rates. Absorption spectroscopy measurements offer the potential of measuring both temperature and species concentration, which is important for better understanding the kinetics within various parts of the fireball (interior, combustion front, and exterior).
In this dissertation, two broadband absorption spectroscopy systems were developed. The first utilizes the visible portion of a supercontinuum laser source for metal oxide absorption thermometry. This system was validated in a benchtop fireball environment produced by metal/ammonium perchlorate powder beds, and measured temperatures of AlO and TiO, key intermediate species to metal combustion. The mean AlO (?2Σ+−?2Σ+, Δ?=0) temperature was 3010 K, whereas TiO had a mean temperature of 2095 K; agreeing well with previous studies. Additionally, single laser-shot and 100 kHz acquisitions were demonstrated.
The second system uses a MEMS-VCSEL source, coupled with a booster optical amplifier, in the near-infrared for water vapor absorption of clean and metalized charges initiated in an 8 cubic meter blast chamber. Hardened laser absorption gauges were constructed to protect the optical components in the explosive environment. Beam steering effects were analyzed for these gauges. The late generation gauges provided sufficient signal retention, and water absorption spectra of clean and metalized charges were obtained. Measured temperatures were lower than expected, however, the peak temperatures of charges with 60 wt. % H-5 aluminum were 200 K higher. Lower peak temperatures were attributed to the flow impediment of the laser absorption gauge, which prevent sufficient mixing in the laser probe volume, and a small charge relative to the large blast chamber volume. Water column densities were independent of time and energetic material formulation; these measurements were validated with equilibrium calculations and a collocated fine-wire thermocouple. This work demonstrates the feasibility of broadband absorption measurements in metalized fireballs.
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Type
dissertation