Burning rate of solid homogeneous energetic materials with a curved burning surface

Abstract

We study experimentally the combustion of a double-based solid propellant NB at a pressure of p = 1 bar, and show that combustion occurs in the cellular-oscillating mode: combustion occurs in the form of separate cells that periodically appear on the burning surface, move along it and disappear. We show that in this mode, a carbonized skeleton is formed on the burning surface, consisting of products of incomplete decomposition of propellant. This skeleton is associated with the burning surface and plays an important role in maintaining the cellular-oscillating mode of combustion of the double-based propellant. To explain the experimental data, we consider a combustion model with a curved burning surface. We show that the burning rate depends on the curvature of the burning surface: with increasing curvature of the burning surface, the local burning rate decreases and combustion becomes impossible if the nondimensional radius of curvature (Michelson-Markstein criterion) of the burning surface becomes less than some critical value. The calculated critical value of the Michelson-Markstein criterion is in good agreement with that obtained in experiments. Using the developed model of combustion of solid homogeneous energetic materials (SHEMs) with a curved burning surface, we calculate the critical combustion diameter of various SHEMs and the shape of stationary cells on the burning surface. The critical combustion diameters of various SHEMs calculated in this way we compare with the available experimental data. A good agreement between the theory and experiments was obtained.