A thrust augmented nozzle for hybrid rocket systems is investigated. The design leverages 3-D additive manufacturing to embed a helical fuel port into the thrust chamber of a hybrid rocket burning gaseous oxygen and ABS as propellants. The helical port significantly increases fuel regression rate, resulting in a fuel-rich plume exiting the nozzle throat. When a secondary gaseous oxygen flow is injected into the nozzle downstream of the throat, the hot unburned, pyrolyzed hydrocarbons in the plume spontaneously ignite. This secondary decomposition produces additional high pressure gasses that are captured by the nozzle and significantly increases the exit pressure. Secondary injection and combustion allows a high expansion ratio nozzle to be effective at low altitudes where there would normally be significantly flow separation and possibly an embedded shock wave. The result is a 15% increase in produced thrust level with no loss in specific impulse due to secondary injection. Core flow specific impulse levels were increased significantly. Control tests performed using cylindrical fuel ports with secondary injection, and helical fuel ports without secondary injection did not exhibit this performance increase. Clearly, both the fuel rich plume and secondary injection are essential features allowing the hybrid thrust augmentation to occur. Techniques for better design optimization are discussed.
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