Regression rate of paraffin-based fuels in hybrid rocket motor

Abstract

Paraffin-based fuels are regarded as a promising solid fuel for hybrid rocket motor (HRM) owing to high regression rate, excellent mechanical performance, and high dropping point. The regression rate of paraffin-based fuels was characterized by static fire test with nitrous oxide (N2O) and gaseous oxygen (GOX) as oxidizer, and the effect of combustion catalyst, injector and chamber pressure on the regression rate was evaluated in this study. The results show that the average regression rates of paraffin-based fuel with GOX and N2O are similar under the optimal oxidizer/fuel (O/F) ratio, and the exponent n is larger with GOX as the oxidizer, indicating high sensibility to oxidizer mass flux. The average regression rate increased with the increase in swirling number Sg, and the tangential injector with Sg of 6.83 improved the regression rate significantly. The local regression rate unchanged with axial position when a jet injector was used, but a complex local regression rate appeared at the first half of fuel grain for tangential injector. Both copper chromite and cobalt stearate obviously increased the regression rate; however, only copper chromite could be used as a preferable regression rate improver owing to significant curing acceleration of fuels by cobalt stearate. The average regression rate slightly increased with the increase in chamber pressure with GOX as the oxidizer, but a noticeable positive relationship could be found for the cases of N2O.