Effects of gas-phase thermal expansion on the stability of deflagration through a porous energetic material

Conference · Sun Jan 01 04:00:00 EST 1995

OSTI ID:6154026

Margolis, S B ^[1]; Williams, F A ^[2]

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1. Sandia National Labs., Livermore, CA (United States)
2. California Univ., San Diego, La Jolla, CA (United States). Dept. of Applied Mechanics and Engineering Sciences

The propagation of a deflagration wave through porous energetic materials, as in the case of strictly condensed-phase combustion, is subject to intrinsic diffusional/thermal instabilities that can lead to various oscillatory modes of burning. Under the assumption that the gas phase may be regarded as ideal but quasi-steady, asymptotic analyses are developed for the nonsteady, nonplanar deflagration of porous energetic solids, such as degraded nitramine propellants, that experience significant gas flow in the solid preheat region and are characterized by the presence of exothermic reactions in a bubbling melt layer at their surfaces. Relative motion between the gas and condensed phases is taken into account in both regions, and the derived asymptotic model is analyzed to obtain an explicit solution for steady, planar deflagration and a dispersion relation describing its linear stability. The present analysis parallels a similar study by the authors that allowed for a fully nonsteady gas phase, but neglected the effects of gas-phase thermal expansion. Nonetheless, qualitatively similar results are obtained, predicting a pulsating neutral stability boundary in the nondimensional activation energy - disturbance wavenumber plane beyond which nonsteady, nonplanar solutions are anticipated. Focusing on the realistic limit of small ratios of gas-phase to condensed-phase density and thermal conductivity, it is demonstrated that the effect of a nonzero porosity a, of the unburned solid material is generally destabilizing. The effect of gas-phase thermal expansion is also shown to be destabilizing, further suggesting that degraded propellants, which exhibit greater porosity than the pristine material, may be especially prone to nonsteady deflagration.

• Research Organization: Sandia National Labs., Livermore, CA (United States)
• Sponsoring Organization: DOE; DOD; USDOE, Washington, DC (United States); Department of Defense, Washington, DC (United States)
• DOE Contract Number: AC04-94AL85000
• OSTI ID: 6154026
• Report Number(s): SAND-95-8456C; CONF-950720--1; ON: DE95004382
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400800* -- Combustion
Pyrolysis
& High-Temperature Chemistry
ASYMPTOTIC SOLUTIONS
CHEMICAL REACTIONS
COMBUSTION
DISPERSION RELATIONS
EXPANSION
FLUID FLOW
FLUIDS
GAS FLOW
GASES
INSTABILITY
MATERIALS
OXIDATION
POROUS MATERIALS
THERMAL EXPANSION
THERMOCHEMICAL PROCESSES
TWO-PHASE FLOW