The effects of SiO2 and TiO2 on the two-phase burning behavior of aqueous HAN propellant
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2018 The Combustion Institute. Silica and titania nanoparticles were included at mass loadings of 1% and 3% in aqueous HAN propellants to evaluate their effects on liquid- and gas-phase decomposition and combustion. Both the liquid-phase and overall burning rates of propellant formulations were indirectly measured in a constant-volume strand burner filled with Argon from pressures of 3-22 MPa using a novel, pressure-based method developed by the authors in recent work. This approach provides overall burn times for propellants such as aqueous HAN which continue to burn beyond the disappearance of the liquid, making it superior to methods based solely on visual observation which only monitor the liquid surface regression. The presence of silica nanoparticles increased the liquid-phase burning rate in the low- and medium-pressure regimes (<10 MPa) and increased the overall burning rate at all pressures evaluated. The maximum amount of burning rate enhancement was realized at the lowest evaluated pressure (3 MPa) which corresponded to 80% and 670% increases in the liquid-phase and overall burning rates, respectively, for a silica loading of 1%, and 160% and 830% increases in the liquid-phase and overall burning rates, respectively, for a silica loading of 3%. The presence of titania did not measurably affect the liquid-phase burning rate, but it did increase the overall burning rate in the low-pressure regime (<5.7 MPa). This low-pressure overall burning rate enhancement was not amplified by further titania loading from 1% to 3% and was maximized at the lowest evaluated pressure (3 MPa) which corresponded to a 500% increase in the overall burning rate. The observed enhancements of the propellant's liquid-phase and overall burning rates were attributed to the presence of catalytic processes which diminish at higher pressures. This work represents the first time nanoparticle additives have been utilized to tailor the combustion of liquid HAN-based monopropellants.
