Performance characterization of hybrid rocket fuel grains with complex port geometries fabricated using rapid prototyping technology

Rapid prototyping has developed to the point that it can be used to print solid-fuel grains for hybrid rockets. Multijet modeling has been used by The Aerospace Corporation to print composite cell structures of acrylic filled with paraffin wax, allowing for both structural strength and fast regression rate. Grains of this kind show promise for applications such as small satellite or CubeSat thrusters. These grains, among other printed and cast designs, have been tested in the long grain center-perforated (LGCP) hybrid rocket motor at The Pennsylvania State University. Parameters such as chamber pressure, regression rate, and combustion efficiency were calculated to characterize each solid-fuel grain geometry. Focus was placed on designs in which swirl is induced within the grain through printed channels or vanes, but grains with swirl induced through oxidizer injection were also tested as a means of comparison and to further characterize the LGCP injectors. An experimental reduction technique was developed in SolidWorks to characterize regression rate and oxidizer mass flux for complex port geometries, which would otherwise be impossible to determine using conventional methods. Composite honeycomb grains were found to have regression rates comparable to cast paraffin wax standards and, depending on cell size, potentially much higher combustion efficiency. Swirl injection has been shown to produce increases of fuel regression rate around 30% in pure cast paraffin and 40% in cast paraffin with the addition of aluminum particles. In addition, grains containing turbulator vanes were shown to have regression rate enhancements similar to those of straight-port grains subjected to swirl injection.