Performance Comparison of Paraffin/Ethanol Fuel Blends in a Laboratory-Scale Hybrid Rocket Motor

This paper discusses the performance characteristics of a paraffin-based blend of liquid ethanol with paraffin as compared to pure paraffin in a hybrid rocket motor. Since the disclosure of the high regression rates of liquefying fuels as compared to classic fuels such as hydroxyl-terminated polybutadiene (HTPB), many studies using paraffin have been reported in the literature. Although pure paraffin regresses three to four times faster than HTPB, it is not an ideal fuel for launcher applications for the following reasons: it does not provide the optimum mechanical strength, it may suffer from combustion instability, and it offers low combustion efficiency. The proposed blend is biphasic, with drops of liquid ethanol trapped in a paraffin binder; and a nonionic surfactant was employed to emulsify the ethanol into paraffin wax. The results indicated that at a mean prefiring O/F of 0.6 and a G(ox) of 60, both the P95E05 and P90E10 fuels demonstrated no significant statistical difference compared to pure paraffin in terms of thrust, specific impulse, fuel mass flow rate, characteristic velocity, and combustion efficiency. However, the P95E05 and P90E10 fuels did show damping in the pressure oscillations relative to paraffin, indicating a reduction in the low-frequency combustion instability observed in the ballistic responses of paraffin.