Microwave enhancement of energetic materials combustion through gas-phase flame interactions
Traditionally, energetic materials’ energy output has been limited to being controlled via formulations and, once an energetic material is manufactured, dynamic change of energy output during combustion is difficult. These limitations are specific to all types of energetic materials, including propellants and pyrotechnics. Thus, a new robust method is needed to control energetic materials' energy release. This work explores microwave interactions with energetic material multiphase flames through interaction with the gas-phase of an energetic material to address these limitations. This dissertation discusses three studies on microwave enhancement of combustion of both composite solid propellants and Mg-based pyrotechnics. First, solid propellant flames were studied in microwave fields at atmospheric pressure. Through doping of the composite solid propellant with alkali metal (i.e., sodium nitrate, NaNO3), flame ionization and free-electron population were able to be enhanced, allowing more efficient collisional microwave energy transfer to the flame and higher steady-state propellant burning rate enhancement of up to 60%. The second study examined the use of microwave energy to modulate the light emission intensity and/or light emission color of a pyrotechnic flame. Microwave field interaction with pyrotechnics comprised of magnesium (Mg) fuel and an oxidizer (alkali-nitrate of sodium, potassium, or cesium) is studied. Light emission enhancement of up to 120 % in the visible range is demonstrated, which has little effect on flame emission chromaticity. The third investigation area explored the color-shifting abilities of an Mg/PTFE pyrotechnic with low free-electron populations. Color shifting was demonstrated in the diffusion flame of the pyrotechnics, where this emission enhancement primarily occurs from excitation of molecular electronic transitions and continuum emission. Gray body continuum temperature fits showed an increase in flame temperatures of ~100-300 K. These studies illustrate the many different mechanisms through which microwave energy can interact with the multiphase flame environment of energetic material and several different useful combustion responses produced from microwave illumination.