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Nanoaluminum powder (nAl, nominal size of particles 50 nm and 100 nm), obtained by electrical explosion of wires, was passivated by air and coated by several different protective organic reagents to assess the effects on ballistics of nAl-loaded hydroxyl-terminated polybutadiene (HTPB)-based solid fuel with respect to pure HTPB baseline. The nAl samples were characterized by transmission electron microscopy (TEM), Brunauer–Emmett–Teller (BET), and chemical analysis on active aluminum content (Al°) content and added to HTPB-based solid fuels for hybrid propulsion. Combustion tests were carried out burning central-perforated single-port cylindrical samples in a 2D radial burner. Data analysis was performed to obtain a continuous time-resolved regression rate. Coated nAl particles may significantly improve the ballistics of HTPB + nAl formulations burning in gaseous oxygen, with respect to pure HTPB. All investigated formulations with nAl exhibit increase of instantaneous regression rate (up to 89% maximum), depending on coatings and oxidizer mass flux G ox . Fluoroelastomer and fluorine-containing chemicals used for coating show a good compromise between increase in regression rate and low sensitivity to G ox variation under the implemented operating conditions

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Low regression rates limit application of hybrid rocket engines (HREs). In this paper, combustion of HTPB-and solid para©n wax-based fuels is investigated in a lab-scale burner by a time-resolved optical technique. The e¨ects of pressure are explored over the range 7 to 16 bar. Nanosized (ALEX TM , 100 nm, uncoated) and micronsized (MgB composite, 5 µm) metal additives are tested. For all runs, the instantaneous regression rate is not constant but higher at the beginning of tests. Overall, MgB performance and relatively ease of manufacturing enable to consider this additive as an interesting novel candidate to enhance hybrid rocket engines performance. NOMENCLATUREA space-averaged value (of parameter A) A time-averaged value (of parameter A) 2D two-dimensional a multiplicative factor [Eqs. (1) and (5)