Effect of Different Injectors on Performance of Hybrid Rocket Motor by Varying the L/D Ratio

The present study aimed to compare the effect of swirl injection on the regression rate and combustion efficiency of a hybrid rocket using two different lengths to diameter (L/D) ratios for the motor: 9.5 and 17. The fuel used was HTPB, and the oxidizer used was GOX. The significance of using a swirl injector is that it introduces an additional tangential velocity component, in addition to the axial component of conventional showerhead injectors, in the hybrid rocket motor. For the larger motor of 340 mm, it was observed that the improvement in regression rate was achieved only up to a length of 210 mm. This implies that the head end swirl injector was not capable of providing a swirling flow all the way to the nozzle end. When comparing the regression rates of the showerhead and swirl injectors for the 190 and 340 mm motors, an increase was observed in the case of swirl injection. Study revealed that in terms of combustion efficiency, the showerhead injector and the swirl injector exhibited contrasting results for the 190 mm motor. Specifically, the swirl injector demonstrated an 11% increase in combustion efficiency compared to the showerhead injector. However, for the 340 mm motor, the increment in combustion efficiency was comparatively lower at 6%.