Simulation and Analysis of the Ignition Flow Field at the Bottom of a Small Cartridge with Densely Packed Granular Propellant

To address the issue of point ignition efficiency caused by the dense packing of granular propellant in miniaturized ejection devices, this study determined that the ignition efficiency at the bottom of the small cartridge is sufficient to meet requirements. By combining the Blender physics engine with ANSYS SpaceClaim scripting and modeling technology, a three-dimensional random packing model was constructed. Fluent fluid-structure interaction simulations analyzed the effects of vertical, horizontal, and mixed drop methods on ignition characteristics. The Realizable k-epsilon turbulence model was used to simulate the transient flow of high-pressure gas, quantifying ignition efficiency by the fuel surface ratio. At a certain ignition pressure, it was found that the fuel surface ratio growth rate for vertical and mixed drop filling methods was higher (with differences < 3% within 0.25 ms). Further analysis indicated that horizontal drop filling led to an 8.7% reduction in the internal hole fuel surface ratio due to the axial alignment of the propellant particles with the ignition direction. The temperature field and flow velocity cloud diagrams showed that under the bottom ignition structure, gas can form a continuous high-temperature zone in disordered gaps, with a uniform propagation speed gradient in the vertical direction. The fuel surface formation time (0.25 ms) is much shorter than the combustion cycle (> 10 ms), and the differences in fuel surface ratio among the three filling methods have a limited impact on overall combustion.