Validation of Numerical Simulations for Nano-Aluminum Composite Solid Propellants

Abstract

Nano-Aluminum is of interest as an energetic additive in composite solid propellant formulations for its demonstrated ability to increase combustion efficiency and burning rate. However, due to the current cost of nanoaluminum and the safety risks associated with propellant testing, it may not always be practical to spend the time and effort to mix, cast, and thoroughly evaluate the burning rate of a new formulation. To provide an alternative method of determining this parameter, numerical methods have been developed to predict the performance of nanoaluminum composite propellants, but these codes still require thorough validation before application. For this purpose, six propellant compositions were formulated, fully characterized, and burning rates were measured at several pressures between 34.0 and 129.3 atmospheres at room temperature, 20 C, and at an elevated temperature of 71.1 C to test the code's ability to predict pressure-dependent burning rate and temperature sensitivity. To ensure the most accurate model possible, special emphasis was placed on characterizing the size distribution of the constituent nano-aluminum and ammonium perchlorate powders through optical diffraction or optical imaging techniques. Experimental burning rate is compared with the propellant combustion model and shows excellent agreement within 5% for a range of formulations and pressures, however, under other conditions the model deviates by as much as 21%. An analysis of the results suggests that the current framework of the numerical model is unable to accurately simulate all the combustion physics of high-aluminum content propellants, and suggestions for improvements are identified.

MD-DFT Calculations on Dissociative Absorption Configurations of FOX-7 on (001)- and (101)-Oriented Crystalline Parylene Protective Membranes

“…The -NH-and -O=N-Obonds in the decomposition products have unsaturated orbitals and thus high electrostatic potentials that attract the surface electrons of the exposed toluene and methyl groups of the (101)-and (001)-oriented parylene membranes [11], as illustrated in Figure 12. Thus, active electrons are transferred from the highest occupied molecular orbitals (HOMOs) on the -NH-and -O=N-O-groups of the decomposition products to the lowest unoccupied molecular orbitals (LUMOs) on the active adsorption sites on the parylene surfaces [13]. Therefore, the high-energy -NO 2 bonds in the decomposition products of FOX-7 are passivated by the toluene and methyl groups, which is consistent with the results for FOX-7.…”

“…These electrostatic interactions cause the FOX-7 surface electrons to overlap with the parylene membranes, leading to the formation of new short-range intermolecular H-bonds. The adjacent -NH 2 groups continue to interact with the π-bonds to provide the missing electrons to the -NO 2 -benzene unit until the O-H bonds break [13]. The corresponding energy differences (∆E) between the adsorption models and single systems are the lowest (parylene C: −11 kcal•mol −1 ; parylene F: −130 kcal•mol −1 ; parylene AF4: −7.5 kcal•mol −1 ; parylene AF8: −10 kcal•mol −1 ), as shown in Figure 5b.…”

“…The FOX-7 molecule decomposes into -ONO and -OC(NO 2 )=CN 2 H 4 , which have unsaturated bonds with high electrostatic potentials that can attract or repel the surface electrons of protective membranes [12]. Hence, a dissociative adsorption mechanism is possible, depending on the particular surface sites involved [13]. Therefore, the protective membranes required for this compound should have low sensitivity, good flexibility, and mechanical strength, and should be incompatible with organic molecules [14].…”

A mechanism for shattering microexplosions and dispersive boiling phenomena in aluminum–lithium alloy based solid propellant

“…The ammonium perchlorate (ATK, 20 μm and 200 μm, size distributions can be found in Ref. [30]) was added in an 80/20 wt.% coarse to fine ratio, and the hydroxyl-terminated polybutadiene binder (Firefox, R45M) was cured with 11.5 wt.% aromatic polyisocyanate curative (Desmodur, E744). The two additives that were compared were: A.)…”