Development and Preliminary Testing of Paraffin Hybrid Rocket Fuel Grains with Helical Port Structures

Hybrid rockets can be good propulsion alternatives to solid and liquid rockets due to their combined safety, controllability, and high energetic performance attributes. However, their characteristic low fuel regression rates, implying low thrust, may be a significant drawback in the application of hybrid rocket systems. In this research study, we experimentally investigated employing a fuel grain with a helical-shape port as a method to increase motor thrust. A series of static firing tests using gaseous oxygen as the oxidizer and polyester fuel grain with a helical port showed an increase up to 2.5-fold in the regression rate compared to a regular straight cylindrical port. Moreover, the addition of 5% expandable graphite (EG) to the fuel revealed a threefold increase in the regression rate. By relating the fuel consumption solely to the gain size (length), an even further increase in the apparent regression rate was observed-up to fourfold for plain polyester and sixfold for polyester with the 5% EG additive. The enhancement in the regression rate along with the longer internal flow path implies a substantially higher fuel mass flow rate from a given fuel grain, enabling a remarkable increase in the motor thrust or noticeable shortening of the fuel grain and motor, which results in a lighter and smaller rocket motor with improved performance.

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

Martins,

de Souza,

Boschi

et al. 2023

Journal of Propulsion and Power

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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 [Formula: see text] of 0.6 and a [Formula: see text] 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.

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Development and Preliminary Testing of Paraffin Hybrid Rocket Fuel Grains with Helical Port Structures

Cited by 6 publications

References 20 publications

Three-dimensional printed metal-nested composite fuel grains with superior mechanical and combustion properties

Three-dimensional printed metal-nested composite fuel grains with superior mechanical and combustion properties

Enhancing Hybrid Motor Thrust by a Helical-Port Fuel Grain

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

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