Distributed-tube-injector-configured hybrid rocket motor with high thrust density

Abstract

The instability of combustion and low rate of fuel regression of the traditional hybrid rocket motor limit its applications. The distributed tube injector (DTI) presents a promising solution by significantly enhancing average fuel regression rates up to 8 mm/s, while maintaining stable combustion, particularly at the laboratory scale. In this study, we investigate the DTI at high fluxes to determine the characteristics of stability of combustion in hybrid rockets. We conducted tests by using motors with paraffin-based fuel and nitrous oxide in the blowdown mode. They were configured to run at fluxes of around 800 kg/(m2 & sdots). Data from 13 hot-fire tests showed that pressure oscillations in the chamber did not exceed 0.5 bar, thus demonstrating that the DTI-configured hybrid motor could operate smoothly even at motor fluxes that were nearly four times higher than those of traditional hybrid motors. We also verified the capability of the DTI to improve the regression rate. The average regression rate of DTI-configured motors exceeded 6 mm/s, while classically configured hybrid motors achieved a rate of only about 1.5 mm/s at similar fluxes. The insights obtained from the tests can inform the design of hybrid motors that require a high thrust density.