Innovativa metallized nanosized additives for hybrid rocket propulsion

The ballistics of solid fuel formulations loaded with innovative nano-sized Aluminum-Copper (Al-Cu) composite powders was investigated. The tested powders were produced by electrical explosion of wire. Different powders were produced in order to evaluate composition and coating effects. In order to evaluate composite metal effects on fuel regression rate, Copper mass fraction in the starting exploding wire ranged from 0% to 100%. Coating effects were evaluated comparing uncoated particles with coated variants. The coating was realized with FluorelTM and Telomer n5. The produced powders were characterized by SEM,TEM, and DSC-TGA. Tested solid fuels were based HTPB loaded with 10 % additive (by mass). Combustion tests were performed using GOX as oxidizer, with combustion chamber pressure of 1.0 MPa and initial oxidizer mass flux (Gox) of ~390 kg/(m2s). Cured HTPB was considered as baseline for the relative grading of the loaded fuel formulations. Formulations loaded with Al15-Cu85, and Al74-Cu26 showed regression rate enhancement with respect to baseline. Fuel regression rate percent increase for both formulations is higher than 15% for Gox = 350 kg/(m2s) and 23 % for Gox = 150 kg/(m2s). Due to the increased density of the Al-Cu powders with respect to ALEXTM, mass burning rate enhancement of Al-Cu loaded fuels is even higher. For HTPB + 10% Al15-Cu85, mass burning rate enhancement at Gox = 350 kg/(m2s) is 49 %. The ballistics of tested Al-Cu powders exhibit no clear relationship between Cu content and achieved regression rate variations. When compared to the uncoated counterparts, coated variants of the tested powders exhibit performances characterized by a general reduction of the regression rate at high oxidizer mass fluxes. On the other hand, regression rate of coated powders shows a reduced Gox sensitivity. The fuel formulation based on HTPB + 10% Coated Al15-Cu85 exhibits r_f ~ G_ox^0.5. The latter feature appears particularly interesting for hybrid fuel ballistic performance improvement since reduced Gox sensitivity could reduce performance shift during burning