Demko, Andrew Robert (2017-05). Advancements in Composite Solid Propellant Testing and Evaluation for Formulations Containing Novel Nano-Additives. Doctoral Dissertation.
Composite solid propellants are typically used in rocket propulsion systems due to their simplicity and relatively low cost. They are mixtures of the fuel, oxidizer, and various catalysts. Oftentimes, bonding agents and plasticizers are added to improve the mixture and propellant qualities. The advent of the nano-particle synthesis revolution allows for customized particle synthesis. This dissertation outlines two innovative experiments developed at Texas A&M University to study the combustion efficiency and the ignition properties of composite propellants with and without advanced nano-additives. This study first presents new insight and possible advantages unique only to closed-bomb strand burners for the testing of composite solid propellants. However, little information on the combustion efficiency has been reported with strand burner testing. The advantages of a closed-bomb burner is revealed in the present work for the first time by relating the observed pressure rise to a quantitative measure of combustion efficiency through the use of temperature change approximations. The pressure rise is an indication of the flame temperature from the propellant combustion products that mix with the inert gas (argon) in the chamber. Baseline propellants of diverse ammonium perchlorate (AP) particle size distributions were tested at 80% AP and 20% HTPB by weight. Then, using the highest-performing AP, propellants of 85% mono- and bi-modal AP distributions were tested, resulting in a clear comparison of their relative effects on the propellant burning efficiency. The pressure rise study concluded with comparing combustion efficiencies of the synthesis methods of metal oxide catalysts in both aluminized and non-aluminized AP and hydroxyl-terminated polybutadiene (HTPB) propellants. Plotting a normalized pressure rise compared and the mean test pressure indicated that the propellants with narrow AP particle size distributions burn more efficiently. Using simplified models, changes in flame temperature were calculated, and corresponding changes in the relative combustion efficiency were found. Chemical c* efficiency changes were approximated using the constant-volume strand burner for different AP particle sizes and titania synthesis methods. The second focus is on developing a method to evaluate the ignition delay times of similar propellant formulations. Ignition delay time measurements on solid energetic materials lead to better fundamental understanding of the ignition process and provide benchmark data for improving models of the ignition process. This study focused on the validation of ignition delay times of AP/HTPB-based solid propellants with and without aluminum and compared various metal-oxide nanoparticle catalysts. A CO2 laser with a wavelength of 10.6 ?m was operated to obtain a quantifiable and reliable ignition event over a power range of 30 to 100 W. This study developed a method to measure the ignition delay time for AP/HTPB propellants at elevated pressures. The ignition delay time results were compared to literature values for similar conditions. Additional studies to examine the effects of in-situ titania nanoparticles on the ignition delay times demonstrated that the nano-additives only appeared to alter the ignition behavior of the aluminized APCP. From the results of these ignition experiments, it can be concluded that additives, which aid in the low-temperature decomposition of AP, such as Fe2O3, are believed to impact the ignition delay times the most