Effect of multi-location swirl injection on the performance of hybrid rocket motor

Abstract

An attempt has been made in the present study to realize the effect of multi-location swirl injection on the improvement of regression rate and combustion efficiency of hybrid rocket by using two different length to diameter (L/D) ratio of the motor. It is 12 and 24. The fuel used for the study was Polyvinyl chloride (PVC)-Dibutyl Phthalate (DBP) in the ratio of 50:50. The gaseous oxygen was used as the oxidizer. The significance of this method is that a single swirl injection at the head end of the hybrid rocket is not sufficient to provide swirling flow till the nozzle end, if the length of the motor is sufficiently long and the regression rate decreases beyond certain length. In the present study, it has been observed that the 220 mm length is sufficient to get the improvement with single swirling injection. For the 24 L/D motor, the use of multi-location swirl injector motor gave twice the improvement in regression rate compare to the conventional hybrid rocket motor where showerhead injector has been used. Combustion efficiency obtained with multi-location swirl injection gave lower improvement with 24 L/D motor (from 70% to 76%), but the improvement was significant with 12 L/D motor with single swirl injector (from 50% to 74%). Improvement in regression rate as well as the efficiency was observed to be significant, if the mid injector was used as the cavity instead of supplying oxygen through it. The value of mass flux exponent (n) was observed to be 0.51 with multi-location swirl injection and the relatively uniform regression rate from head end to the nozzle end was observed.