Hybrid rockets produce fuel regression rates typically 25% lower than solid fuel motors of the same thrust level. These lowered regression rates produce unacceptably high oxidizer-to-fuel (O/F) ratios that produce a potential for motor instability, nozzle erosion, and reduced motor duty cycles. To achieve O/F ratios that produce acceptable combustion characteristics, traditional cylindrical fuel ports are fabricated with very long length-to-diameter ratios. These high aspect ratios result further reduced fuel regression rate and thrust levels, poor volumetric efficiency, and presents the potential for lateral structural loading issues during high thrust burns. Results from a development campaign that uses additive manufacturing to fabricate hybrid rocket fuel grains with embedded helical fuel port structures are presented. Both gaseous oxygen and nitrous oxide were used as the oxidizer with acrylonitrile butadiene styrene as the fuel material. Centrifugal flow patterns introduced by the embedded fuel port structures dramatically increase fuel regression rates by enhancing surface skin friction, and reducing the effect of boundary layer "blowing" to enhance convective heat transfer to the fuel surface. Regression rate increases by a factor approaching 3 were observed. The helical fuel port also increases the volumetric efficiency of the fuel grain by lengthening the internal flow path.
展开▼
