Condensed Phase Product Penetration and Flame Spreading Processes in Granular Propellant Bed

Abstract : Understanding the detailed ignition, flame-spreading, and combustion processes inside of a granular solid-propellant bed is vital for accurate interior ballistic modeling, and for the development of ballistic propulsion systems. Experiments were conducted to investigate both the penetration characteristics of pyrotechnic igniter jets, and the subsequent flame spreading processes in a granular bed. The experiments utilized both live and inert propellant, in conjunction with high-speed photography and photodetectors. A singular igniter jet was discharged axially into an inert granular bed. This setup was designed to study the region of particles coated by the condensed-phase products of the igniter jet. This information is very useful since the ignition behavior of live propellants is dependent upon both convective heating by the igniter jet as well as conductive heating by the deposited condensed-phase products. Three correlations were developed that describe the region of the granular bed coated by the condensed-phase products from the igniter jet; these include: 1) the axial depth of penetration, 2) maximum radial penetration, and 3) the volume of the coated region. These parameters were found as functions of the Reynolds number based on the operating conditions of the igniter jet and granular bed.