Date of Award
Doctor of Philosophy
James B Michael
Solid propellants are widely utilized in rocket motors due to their high mass fraction. Recently, alkali-doped aluminized solid propellants have been demonstrated for enhancing burning rate using microwave-based plasma, where a significant increase in atomic sodium and aluminum particulate emission was observed. The details of energy deposition during microwave-field and plasma-enhancement remain unclear but require measurements of both gas-phase species and condensed phase particulates to understand the degree of deposition and avenues for optimizing controlvia field applications. In this dissertation, an optically accessible microwave test section for propellant strand burning was instrumented with several optical emission techniques for thermometry. These optical techniques in microwave-enhanced propellant flames were applied to measure Na electronic temperature, AlO vibrational temperature, and both Al droplet and product plume condensed-phase temperatures. This set of measurements detailed the degree of temperature rise for species, showing increases in the Na electronic temperature of > 1200 K, and a more modest increase of 120 K in the AlO vibrational temperature. Droplet temperatures were found to be unchanged, as the droplet temperature is fixed to the boiling point of the liquid aluminum. However, significant increases of ∼ 700 K were measured in the product plume, suggesting that deposition to condensed phase metal-oxide species might take place for a range of electric field frequencies outside of any plasma formation process. Based on these temperature increases, approximately ∼ 50 W of energy was deposited in this subset of constituents. To support the thermometry measurements of plasma-enhanced propellant combustion, several laser-induced fluorescence studies were undertaken. A novel two-photon laser-induced fluorescence of sodium showed the advantages of reducing particle scattering and improved signal-to-noise ratio imaging. In addition, a rate equation numerical model was developed, including the calculation of the multiphoton absorption and ionization cross-sections, and results matched well with experiments. Another two-photon excitation of the CN radical was explored in gas-phase flames utilizing an ultrafast broadband 1 kHz laser system that has the potential to capture flame dynamics. Finally, digital in-line holography was utilized to measure aluminum agglomerate sizes and velocities in different propellant formulation flames. Improved velocity correlations can result in better numerical models and a better understanding of the aluminum combustion mechanisms in propellants.
Zhu, Keke, "Optical measurements in multiphase combustion" (2021). Graduate Theses and Dissertations. 18651.