Nonideal regimes of deflagration and detonation of black powder
ABSTRACT The explosive and deflagration properties of black powder differ significantly from those of modern propellants and compositions
based on ammonium nitrate or ammonium perchlorate. Possessing a high combustibility, black powder is capable of maintaining
stable combustion at high velocities in various shells, be it steel shells or thin-walled plastic tubes, without experiencing
deflagration-to-detonation transition. It is extremely difficult to detonate black powder, even using a powerful booster detonator.
The results of numerical simulations of a number of key experiments on the convective combustion and shock initiation of black
powder described in the literature are presented. The calculations were performed within the framework of a model developed
previously for describing the convective combustion of granulated pyroxylin powders, with small modifications being introduced
to allow for the specific properties of black powder. The thermophysical properties of the products of combustion and detonation
and the parameters of the equation of state of black powder were determined from thermodynamic calculations. The calculation
results were found to be in close agreement with the experimental data. The simulation results were used to analyze the regularities
of the wave processes in the system and their relation to the properties of black powder and the experimental conditions.
It was demonstrated that the effects observed could be explained by a weak dependence of the burning rate of black powder
on the pressure.
- SourceAvailable from: Ashwani K. Kapila[Show abstract] [Hide abstract]
ABSTRACT: The two-phase mixture model developed by Baer and Nunziato (BN) to study the deflagration-to-detonation transition (DDT) in granular explosives is critically reviewed. The continuum-mixture theory foundation of the model is examined, with particular attention paid to the manner in which its constitutive functions are formulated. Connections between the mechanical and energetic phenomena occurring at the scales of the grains, and their manifestations on the continuum averaged scale, are explored. The nature and extent of approximations inherent in formulating the constitutive terms, and their domain of applicability, are clarified. Deficiencies and inconsistencies in the derivation are cited, and improvements suggested. It is emphasized that the entropy inequality constrains but does not uniquely determine the phase interaction terms. The resulting flexibility is exploited to suggest improved forms for the phase interactions. These improved forms better treat the energy associated with the dynamic compaction of the bed and the single-phase limits of the model. Companion papers of this study [Kapila et al., Phys. Fluids 9, 3885 (1997); Kapila et al., in preparation; Son et al., in preparation] examine simpler, reduced models, in which the fine scales of velocity and pressure disequilibrium between the phases allow the corresponding relaxation zones to be treated as discontinuities that need not be resolved in a numerical computation.Physics of Fluids 01/1999; 11(2):378-402. · 1.94 Impact Factor