Excessive Subsurface Heat Release As a Possible Cause of the Negative Erosion Effect during Combustion of Homogeneous Solid Propellants

An increase in the burning (gasification) rate of solid propellants exposed to a sufficiently intense gas crossflow was discovered experimentally in the 1940s and called erosive burning. Later it was found that for some propellants at relatively low crossflow velocities, there may be a decrease in the burning rate, called negative erosion. Attempts to theoretically study negative erosion have been made since 1971 and focused on analyzing changes in the intensity of heat transfer on the burning surface with the leading role of gas-phase reactions taking into account the effect of large-scale fluctuations in gas velocity and temperature, the effect of differences in diffusion coefficients and thermal diffusivity of the gas, and the flame stretching effect. This paper presents an analysis of propellant combustion under crossflow conditions in the presence of intense subsurface heat release due to exothermic reactions in the condensed phase. In the case where the surface temperature is limited by the boiling point, local temperature maxima can form in the subsurface layer, resulting in nonuniform reaction on the surface and the occurrence of intrinsic turbulence in the adjacent gas layer. The presence of this turbulence leads to a change in heat transfer to the propellant and allows a qualitative explanation of the negative erosion effect.