Novel hybrid rocket internal ballistic configuration with coaxially located tube injector

Even though hybrid rocket motors offer significant advantages, there are also some drawbacks associated with the systems complications caused by low fuel regression rates. Studies on regression rate enhancement of hybrid rocket motors have been mainly focused on liquefying solid fuels, fuel additives and nonconventional fuel grain – injector designs. It was proven that the liquefied fuels enhance the regression rate by a factor of 3 to 4 compared to the conventional hybrid fuels. This study proposes a new injection concept, tube injector. Rather than injecting the oxidizer axially from the head-end of the motor, oxidizer is introduced radially through a tube injector which is coaxially located on the centreline of the fuel port. Within the scope of this study, an internal ballistic model of the new injection concept was developed. Then, test setup modifications and the manufacturing of the new motor hardware was completed. Finally, three hot firing tests were conducted using a 65 mm diameter N2O motor. The results clearly reveal that a significant enhancement on the regression rate was achieved with this concept compared to the classical axially injected hybrid configuration. When fully matured, this injection scheme along with fast burning liquefying fuels would result in hybrid rocket systems with very short fuel grains, making the packaging much more feasible for operational systems.