Combustion of ammonium perchlorate-polymer sandwiches

This paper reports reacting fluid dynamics calculations for an ammonium percholrate binder sandwichand extracts experimentally observed features including surface profiles and maximum regression rates as a function of pressure and binder thickness. These studies have been carried out by solving the twodimensional unsteady Navier-Stokes equations with energy and species conservation equations and a kinetic model of three reaction steps (ammonium perchlorate decomposition flame, primary diffusion flame, and final diffusion flame) in the gas phase. The unsteady two-dimensional conduction equation is solved in the condensed phase. The regressing surface is unsteady and two dimensional. Computations have been carried out for a binder thickness range of 25–125 μm and a pressure range of 1.4 to 6.9 MPa. Good comparisons at several levels of detail are used to demonstrate the need for condensed-phase two-dimensional unsteady conduction and three-step gas-phase reactions. The choice of kinetic and thermodynamic parameters is crucial to good comparison with experiments. The choice of activation energy parameters for ammonium percholrate combustion has been made with stability of combustion in addition to experimentally determined values reported in literature. The choice of gas-phase parameters for the diffusion flames are made considering that (a) primary diffusion flame affects the low-pressure behavior and (b) final diffusion flame affects high-pressure behavior. The predictions include the low-pressure deflagration limit of the sandwich apart from others noted above. Finally, this study demonstrates the possibility of making meaningful comparisons with experimental observations on sandwich propellant combustion.

Sandwich propellant combustion: Modeling and experimental comparison

The combustion of mixtures of ammonium perchlorate and various inorganic compounds of the following general types was studied: oxides of copper and chromium, oxides of other metals, other perchlorates, other ammonium salts, and darkening agents. The additives were generally added at the 2 and 8 wt% levels. Deflagration rates as a function of pressure (100 <p< 1500 psi) and initial sample temperature (ambient room temperature and 100°C), results from motion picture photography of burning samples are presented and discussed.

Combustion of Ammonium Perchlorate and Various Inorganic Additives

Differences in ammonium perchlorate (AP) combustion behavior as evidenced by the effects of pressure, sample temperature and acceleration environments on burning rate are shown for samples prepared in various manners. The sample preparation parameters investigated include pellet compaction time and pressure, the particle sizes of the AP powder from which samples were pressed, and the type of AP (ultra-pure, propellant grade, and propellant grade with conditioners) from which the pellets were made.

Ammonium Perchlorate Combustion: Effects of Sample Preparation; Ingredient Type; and Pressure, Temperature and Acceleration Environments

The problem of nonmetallized AP/composite propellant combustion is studied with the aim of coherently
interpreting apparently diverse experimental data. Three fundamental hypotheses are introduced: the extent of
propellant degradation at the vaporization step has to be specified through a scientific criterion; condensed phase
degradation of AP to vaporizable fragments is the overall rate-limiting reaction; the rate of combustion in the gas
phase is controlled by diffusive-mixing processes. Theoretical predictions of the regression rates of AP are seen to
match well with experimental observations (both hot-plate pyrolysis and single-crystal deflagration). Theoretical
curves of regression rate are presented for a typical composite propellant. The gas phase processes are discussed
qualitatively. It is seen through analyses that either of the two familiar models for the gas phase (flame sheet
approximation and uniform combustion) describes the general behavior adequately, hence de-emphasizing the
role of gas phase details in propellant combustion.

D. E. Zurn

Papers

The Temperature Sensitivity of the Deflagration Rates of Pure and Doped Ammonium Perchlorate