Formulation and Characterization of Paraffin-based Solid Fuels Containing Swirl Inducing Grain Geometry And/or Energetic Additives

Open Access
Armold, Derrick Michael
Graduate Program:
Mechanical Engineering
Master of Science
Document Type:
Master Thesis
Date of Defense:
April 11, 2014
Committee Members:
  • Kenneth K Kuo, Thesis Advisor
  • swirl injection
  • 3-D printing
  • regression rate
  • combustion efficiency
  • port modeling
Rapid prototyping has developed to the point where polymers or waxes can be printed to serve as solid-fuel grains for hybrid rockets. Complex grain geometries inconceivable with any other method can be fabricated with no additional manufacturing or machining cost. This process has been manipulated to produce composite grains structures of paraffin wax and acrylic or other geometries containing swirl channels or protruding vanes. Printed grains of this size show great promise for applications such as small satellite or CubeSat thrusters. Numerous printed and cast grains have been tested in the Long Grain Center-Perforated (LGCP) hybrid rocket motor at The Pennsylvania State University. Test parameters including regression rate, chamber pressure, and combustion efficiency were calculated to characterize each grain. Focus was placed on grains inducing swirl with internal channels or vanes, although multiple tests were performed using swirl injection as a means of comparison and to further characterize the LGCP injectors. To determine regression rate and oxidizer mass flux for unconventional and complex port geometry a novel modeling method utilizing SolidWorks® was developed. Using this method star-swirl grains of acrylic polymer were found to have regression rate enhancements of up to 250%. Composite honeycomb grains were found to have regression rates similar to those of cast paraffin and, depending on cell size, potentially much higher combustion efficiency. Swirl injection has been shown to produce increases of fuel regression rate around 30% for cast paraffin grains and around 40% in cast paraffin grains with dispersed micron-size aluminum particles. Additionally, turbulator designs were used with cast wax to produce regression rate enhancements similar to those grains straight-port grains subjected to swirl injection.