Solid propellant diffusion flame structure

Abstract

Laser-supported deflagration of ADN, AP, HNF, TNA, RDX, or HMX in sandwich configurations with various energetic and nonenergetic binders was studied. Planar laser-induced fluorescence (PLIF) was used to measure the two-dimensional NH, OH, and CN species profiles for these sandwiches. For the HNF sandwiches, obvious diffusion flames were present at low pressure, but they were weak, further from the surface than the HNF monopropellant flame, and not expected to be burn-rate controlling. ADN was found to have diffusion flames with energetic binders at low pressures, but they were very far from the surface. The high burn rate of ADN at pressures above 3 atm left the binder behind, and the diffusion flames became weak. AP showed clear evidence for strong close diffusion flames with binders and even with other oxidizers. The combination of HMX or TNA with AP leads to obvious diffusion flame interactions: the highly reactive AP-decomposition products accelerated the nitramine dark zone kinetics and caused the secondary flame to hold on the interface region. This leads to higher heat feedback in the interface region and a somewhat faster nitramine regression rate. TNA, RDX, and HMX were not found to have any diffusion flames with energetic or nonenergetic binders: the monopropellant flame was lifted in the region around the binder. These results imply that ADN, HNF, TNA, RDX, and HMX propellants will not have the clear particle size ballistic tailorability seen with AP propellants, because diffusion flames appear to be strong and close to the surface (and therefore burn-rate controlling) only in AP propellants.