Fundamental Processes in Solid Propellant Ignition

Abstract
Analytically and numerically determined behaviour of the diffusion equations, with chemical reactions, describing a gas phase ignition process for homogeneous and composite solid propellants, suddenly exposed to an ignition stimulus, are reported. Stimuli considered are a high pressure and temperature, stagnant gas of specified oxidizer content, or a radiant heat flux impinging on a non-opaque propellant exposed to a low temperature gas phase of specified pressure and composition. The results, assuming a radiant stimulus, indicate that purely gas phase reaction processes play only a minor role in the overall ignition behaviour. Qualitative agreement with experiments is found for several flux and pressure levels. Most interesting are the results using a hot ga stimulus. In homogeneous propellants, ignition involves consecutive development of a primary flame between propellant pyrolysis products, and a secondary flame using unburned fuel from the primary flame and any ambient oxidizer present. A unique calculation of light emission during ignition development allowed direct theoretical/experimental comparison of results. Composite propellants ignite via pyrolysis of the propellant and reaction of fuel species with any ambient oxidizer present, followed by reaction with propellant produced oxidizer species. Matching of gas phase ignition processes produce ignition behaviour in excellent, quantitative agreement with experiments using a hot gas stimulus, regarding effects of ambient gas phase pressure and composition on the ignition delay.

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