Protrusion effect on the performance of hybrid rocket with liquefying and non-liquefying fuels

In the present study, attempts were made to compare the influence of protrusion method on the performance of liquefying and non-liquefying fuels which has different combustion processes in a hybrid rocket motor. The wax and PVC (Polyvinyl Chloride)-DOP (Dioctyl Phthalate) in the 50:50 ratios were used as the liquefying and non-liquefying fuel, respectively with gaseous oxygen as the oxidizer. The regression rate and combustion efficiency of a laboratory scale hybrid rocket motor were determined for the single, double and multi-protrusion cases. The nylon protrusion that regress with burn time was used as protrusion for liquefying fuel and graphite protrusion that do not burn were used as the protrusion for the non-liquefying fuel. The selection of these protrusions was such that the protrusion heights between them are comparable for the given experimental time. It has been observed that the use of three protrusions (0.2–0.5–0.8X/L) gave the highest improvement in regression rate for both fuels. The percentage improvement in regression rate was relatively similar for both the fuels with all the combinations of protrusion used and a minor difference was observed that was due to the difference in the height of protrusion. The improvement in combustion efficiency was observed to give the highest for both the fuels, when the protrusion was placed at 0.8X/L. The relative improvement with single protrusion in non-liquefying fuel was significant (around 42%) while with liquefying fuel it was only 8%. The use of double or three protrusion gave a minor improvement in the efficiency of liquefying fuel but reduction in efficiency was observed with non-liquefying fuel compare to the single protrusion.