One of the primary parameters in the analysis of the performance of the hybrid rocket engine is the regression rate of the solid fuel. Many studies in the past few years have theoretically claimed, or experimentally shown, a possible dependence between the regression rate itself and the chamber total pressure, but no agreement has
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
A closed-loop pulsating heat pipe made of a copper tube (1.1 mm/2 mm I.D./O.D.) and filled with FC-72 has been tested in a large-diameter centrifuge (LDC) of the European Space Agency in Noordwijk at different hypergravity levels up to 20 g, different heat input levels, and different orientations with respect to the gravity direction (vertical bottom heated and horizontal position). The results show that both in the horizontal and vertical orientation the device operation depends on the combined effect of gravity and heat input level. For the horizontal orientation, fluid stratification and the consequent thermal crisis occur at different acceleration levels depending also on the heat input power level and on the heating/gravity history. During the vertical operation, the pulsating heat pipe (PHP) thermal performance is slightly enhanced by the lower hypergravity levels (up to 3 g at 50 W, up to 4 g at 70 W, and up to 6g at 100 W), while two different local thermal crises affect the PHP thermal behavior at higher acceleration levels
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