| Composite Propellant Systems Combustion mechanisms of ammonium nitrate/ammonium perchlorate (AN/AP) mixed oxidizer propellants were investigated in a theoretical manner. The scope of the investigation was to find the way to integrate two independent Granular Diffusion Flame propellant combustion models into one unified model from a fundamental point of view. Two concepts, "oxidizer interaction" and the "scale of the interaction," were introduced. Four different scenarios were created and investigated: (1) a simple superposition of the two independent components, (2) a small-scale interaction model, (3) a large-scale interaction model, and (4) a time-averaging model. These theories were evaluated on experimental results from AN/AP systems by deriving analytical formulae and conducting numerical simulations. Results indicated that (1) there were no common relaxation times between the two components, so that superposition does not satisfy mass conservation, (2) small-scale interaction does not allow the chemical-reaction parameter to decrease rapidly as the AP concentration increases, which is inconsistent with the experimental data, (3) the activation energy averaging (AEA) based on the reaction rate theory and gas pocket mass averaging (GPMA) based on the mass conservation in the gas phase corresponding large scale interaction represent the experimental results very well, and (4) the time-averaging model agrees well only with mass-diffusion while it does not represent the chemical-reaction term. Therefore, a new combustion model for mixed oxidizer composite propellants was verified by using the AEA/GPMA model. |
