| This research was directed toward clarification of the combustion of oxidizer-fuel complexes in heterogeneous solid propellant combustion. Earlier studies used edge burning of oxidizer-fuel laminae as a means to geometrically simplify the details of solid propellant combustion. In the present studies, different sizes of AP particles (10 {dollar}mu{dollar}m, 33.5 {dollar}mu{dollar}m, and 41 {dollar}mu{dollar}m) were included in the binder lamina to investigate how individual AP particles burn and how their combustion couples with the rather well studied sandwich results. In such experiments, the oxidizer laminae played the role of large AP particles, and the AP-filled lamina corresponds to the AP-filled matrix between large particles in the solid propellant. It was relatively easy to test the effects of AP to binder ratio in the lamina (5:5 and 7:3), the effect of AP particle sizes, and of thickness of the matrix lamina.; Combustion photography was used for the measurement of sample burning rates at different pressures for several AP-filled binder thicknesses. Optical and scanning electron microscopes were employed to provide information on the surface details of AP particles in the AP-filled binder, the interface region between the oxidizer and AP-filled binder, and surface profiles of the samples. It was observed that the establishment of individual oxidizer-binder flames does not occur for small AP particles and/or low pressure, whereas the AP particle flame was established for large AP particles and/or high pressure. Roles of the LEFs in more complex systems than conventional sandwiches and flamelet interaction were also investigated. Insights into the different modes of burning of heterogeneous systems resulting from pressure effects, AP particle size effects, and different AP/binder mix ratios were also investigated. The burning rates of 5:5 (10 {dollar}mu{dollar}m), 5:5 (33.5 {dollar}mu{dollar}m), 7:3 (10 {dollar}mu{dollar}m), and 7:3 (33.5 {dollar}mu{dollar}m) AP-filled sandwiches were plotted as a function of matrix thickness, and compared with each other at 300, 500, and 1000 psi. Considering the role of the LEFs, flamelet interaction between large and small AP particles, different modes of burning of heterogeneous systems resulting from pressure effects, AP particle size effects, and different AP/binder mix ratios, the qualitative theory of a flame complex described earlier for PBAN binder was developed for the case of AP particles in the binder. This new expanded flame theory is able to qualitatively predict the burning rate trends, overall surface profiles, and multidimensional flame structures at each pressure and matrix thickness combination. |
