The aging of propellants in PMDs is considered to be one of the primary factors affecting the performance of PMDs. Thus, studies on the aging mechanism of propellants, which have not yet been addressed extensively, pose a solution to securing the sustainable operation of PMDs. We characterized one of the most commonly used commercial propellants (boron potassium nitrate (BKNO3)) and investigated its aging mechanism rigorously. Based on thermal analyses, we demonstrate that the decomposition of laminac, a polymer binder, is the fastest spontaneous reaction. However, it will not self-initiate at a storage temperature as high as 120 °C. The effect of the humidity level was examined by characterizing BKNO3 samples prepared. The heat of reaction and the reaction rate decreased by 18% and 67% over 16 weeks of aging, respectively. This is attributed to the oxide shells on the surface of boron particles. The formation of oxide shells could be confirmed using X-ray photoelectron spectroscopy and transmission electron microscopy–energy dispersive spectroscopy. In conclusion, surface oxide formation with the aging of BKNO3 will decrease its propulsive efficiency; oxidation reduces the potential energy of the system and the resulting oxide decreases the reaction rate.

The combustion of zirconium potassium perchlorate (ZPP) in a closed vessel is modelled and validated through a numerical simulation. Because the extremely high pressure oscillation occurs in less than a millisecond, an in-house computational fluid dynamics (CFD) code is used to observe the detailed flow structures and determine the adequate burning characteristics, including the burning rate. A hybrid RANS/LES scheme with a 5 th order upwind weighted essentially non-oscillatory (WENO) is implemented to capture complex, strong shock waves in highly turbulent combustion. A two-way coupled Eulerian-Lagrangian scheme tracks the combusting ZPP granules reasonably well. Monodisperse and Rosin-Rammler assumptions are applied to the ZPP granule distribution. The monodisperse assumption reveals that the diameter of the ZPP (17 mm) achieves marginal agreement with the measurements. However, the Rosin-Rammler distribution improves the transient and dynamic combustion characteristics in that the small granules contribute to a faster burning rate and stronger shock waves. These results are more analogous to the closed vessel tests used as validation data.

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A parametric study based on an unsteady mathematical model of a pyrotechnically actuated device was performed for design optimization. The model simulates time histories for the chamber pressure, temperature, mass transfer and pin motion. It is validated through a comparison with experimentally measured pressure and pin displacement. Parametric analyses were conducted to observe the detailed effects of the design parameters using a validated performance analysis code. The detailed effects of the design variables on the performance were evaluated using the one-at-a-time (OAT) method, while the scatter plot method was used to evaluate relative sensitivity. Finally, the design optimization was conducted by employing a genetic algorithm (GA). Six major design parameters for the GA were chosen based on the results of the sensitivity analysis. A fitness function was suggested, which included the following targets: minimum explosive mass for the uniform ignition (small deviation), light casing weight, short operational time, allowable pyrotechnic shock force and finally the designated pin kinetic energy. The propellant mass and cross-sectional area were the first and the second most sensitive parameters, which significantly affected the pin's kinetic energy. Even though the peak chamber pressure decreased, the pin kinetic energy maintained its designated value because the widened pin cross-sectional area induced enough force at low pressure.

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