Combustion of Liquefying Fuels with 3D-printed Reinforcement: Metallized Cellular Structures and Loaded Formulations

The armored grain is a heterogeneous fuel formulation consisting of a paraffin-wax matrix reinforced by a 3D-printed cellular structure. The printed structure provides plastic deformability and leads to faster regression rates of the paraffin-based fuels. This study analyzes the influence of metal additives on the regression rate of the armored grain. Two different strategies are considered for loading the armored grain with metal powders: (i) a conventional approach with metal powder dispersion within the liquefying fuel matrix and (ii) loading of the printing material to create 3D-printed metallized structures. Aluminum and magnesium powders are selected as fillers to contrast different combustion mechanisms when a similar particle size (micrometer-size range, 30 − 44 um) is considered. For aluminum, a study of the influence of powder particle sizes and morphology is performed: spherical micron-sized powder is contrasted with its nano-sized counterpart and with flake-Al from mechanical activation. When dispersed in the paraffin-wax matrix, nano-aluminum provides a 43 % regression rate enhancement with respect to the non-metallized armored grain. Similar regression rates are achieved by incorporating spherical 15um aluminum in the printed structure, when burning in oxygen with an oxidizer mass flux in the range 28 − 40 kgm-2s-1. Results from the metalloaded reinforcing structure are promising: significant regression rate increases are achieved with micron-sized powders which are easier to handle and exhibit relatively low reactivity in conventional fuel formulations.