Testing of Hybrid Rocket Fuel Grains at Elevated Temperatures with Swirl Patterns Fabricated Using Rapid Prototyping Technology

Abstract

Hybrid rocket fuel grains fabricated with rapid prototyping technology enable the use of complex internal structures and port geometries. Using rapid prototyping to print features that introduce flow disturbances and increased surface area can result in improved regression rate and combustion efficiency without the need for difficult machining and casting procedures. In some small-scale hybrid rocket applications, such as small satellites or CubeSats, a lack of robust environmental control might require the motor be used at elevated temperature. Additional increase in regression rate can result from firing the rocket motor with an elevated initial fuel grain temperature, however, due to slumping in liquefying hybrid rocket fuels this is also typically accompanied by a decrease in combustion efficiency. In order to characterize the performance of various fuel grains at elevated temperatures, printed fuel grains with a heterogeneous paraffin and acrylic matrix supplied by The Aerospace Corporation were compared with cast paraffin grains using the Long-Grain CenterPerforated hybrid rocket motor (LGCP) at the Pennsylvania State University's High Pressure Combustion Laboratory (HPCL). Results from the LGCP testing showed the effects of initial temperature on regression rate and combustion efficiency. The calculated regression rate and combustion efficiency for each fuel grain was compared to previous testing at Penn State and a correlation previously developed for room temperature paraffin fuels. Regression rate increases of over 20% were found for the heated fuel grains, both printed and cast. As expected, the cast paraffin fuel grains experienced a decrease in combustion efficiency as unburned paraffin wax was expelled from the rocket. The printed fuel grains, however, maintained the combustion efficiency of a room temperature cast paraffin fuel grain. The addition of swept honeycomb cell structures utilizing rapid prototyping technology reduced paraffin slumping and allowed more complete combustion at elevated fuel grain temperatures. Nomenclature HC= Honeycomb HPCL = High Pressure Combustion Laboratory LGCP = Long Grain Center-Perforated hybrid rocket motor SP = Straight Port tpi = Turns Per Inch

Testing and Evaluation of a Double-Tube Hybrid Rocket Motor

“…Thereby, a more uniform combustion of the inner and outer fuels is achieved thanks to the addition of inserts. Consequently, future work of the double-tube configuration would encompass the use of "3D printing" for manufacturing [18][19] more complex inner fuel grains with integrated inserts in a single piece. Additionally, a further understanding of the double-tube operating characteristics is needed for exploiting the full potential of this design.…”

Performance of Additively Manufactured Fuels for Hybrid Rockets

“…However, liquifying fuels are brittle and experience "sloughing", which is where chunks of unburned fuel are expelled from the HRE before fully combusting and results in decreased combustion efficiencies. The effects from sloughing have been shown to increase at elevated temperatures [33].…”

A new strategy for the reinforcement of paraffin-based fuels based on cellular structures: The armored grain — Mechanical characterization

“…The firing test results did not match the theoretical predictions suggesting the presence of unburned paraffin fuel expelled from the ABS structure. Armold et al [28,29] investigated paraffin in a twisted honeycomb structure printed in acrylic. The study focused on the enhancement of the r f and combustion efficiency thanks to the increase of the initial fuel grain temperature.…”

“…The study focused on the enhancement of the r f and combustion efficiency thanks to the increase of the initial fuel grain temperature. Neither McCulley et al [27], nor Armold et al [28,29], conducted mechanical tests on their grains and, to the best knowledge of the authors, no quantitative information on the mechanical properties of structure-reinforced paraffin-based fuel grains is available in the open literature.…”

“…The gyroid is produced by additive production (AM) exploiting fuse deposition modeling (FDM). The AM has already been presented as a method for fuel grain manufacturing [24][25][26], and for the creation of scaffold structures embedding paraffin [27][28][29]. In previous open literature works, the 3D printed grain from AM was considered as the main fuel grain component.…”