Surface Pyrolysis of High Energy Materials

Abstract

The Arrhenius zero-order phenomenological pyrolysis law, commonly used in conjunction with the Vieille ballistic law to study pressure-driven burning of energetic materials, is revisited. Motivated by experimental and theoretical work performed in 1984 in this Laboratory, a relationship among several interplaying parameters is found under steady-state conditions. This relationship corresponds to the Jacobian of the pyrolysis sensitivity parameters used in the Zeldovich-Novozhilov approach. The Arrhenius pyrolysis is still expressed in terms of a global surface activation energy, but consistency with the experimental ballistic law may require an explicit pressure dependence as well. This conclusion is supported by a variety of arguments drawn from different areas. The linear dependence of the pre-exponential factor on surface activation energy (known as kinetic compensation) is proved and extended to the pressure exponent, for any given experimental data set under steady burning. Experimental results are reported for about a dozen solid propellants of different nature. The effects of surface pyrolysis explicit pressure dependence, although modest on steady-state burning, are potentially far -reaching for unsteady regime and/or unstable burning. The paper is mainly focussed on pressure-driven burning and Arrhenius pyrolysis, but the implemented method is believed to apply in general. Thus, enforcing KTSS zero-order, phenomenological pyrolysis with the Vieille ballistic law yields similar results and requires an explicit pressure dependence. In case, the Zeldo\Lich ballistic law is enforced instead of the classical Viei!le law, no explicit pressure dependence is required. The unifying concept for these different trends is the pyrolysis Jacobian as a consistency requirement between the implemented steady pyrolysis and ballistic laws.

Global classical solutions for a free-boundary problem modeling combustion of solid propellants

“…Typically, we may suppose r(ξ ) is a function vanishing below some given ignition temperature T 0 and increasing for ξ > T 0 , as in general observed for onestep, irreversible gasification processes. Specific examples include the standard Arrhenius law or similar [5]. Also, we may assume the conductive heat feedback q g = q g (r) to be a function vanishing as r → ∞ (flame blow-off) and as r → 0 (no burning) and positive for r > 0 (gas phase heats up condensed phase during burning), as observed for one-phase, laminar, nonviscous, low-subsonic, thermal flames.…”