|M.Sc Student||Castaneda David|
|Subject||Hypergolic Ignition of a Hybrid Rocket Motor|
|Department||Department of Aerospace Engineering||Supervisor||Professor Benveniste Natan|
Hybrid rocket systems have the potential to high performance and wide operational capabilities, as well as throttling and shutdown. An essential component in any rocket system is the ignition mechanism. The ignition mechanism should allow initiation of proper burning, as well as ignition-shutdown-re-ignition capabilities. Currently, the ignition of hybrid motors is generally achieved by the addition of an external source or by a consumable catalytic bed (CCB), resulting in more complex and heavy systems.
In the present work, a hypergolic hybrid rocket motor is proposed to obtain a more efficient ignition system. The hypergolic ignition proposed, i.e., ignition of the fuel upon contact with the oxidizer, allows very short ignition delay times and shutdown - re-ignition capabilities without any need of external systems that add weight, length and complexity to the motor. The hypergolic ignition is achieved by embedding a catalyst or a promoter, which is hypergolic with the liquid oxidizer, into the solid grain. The hypergolic reaction between the catalyst and the oxidizer is highly exothermic and enough to cause the ignition and combustion of the solid fuel together with the oxidizer. In the present study, different catalysts and fuels were tested with high concentration hydrogen peroxide, via drop-on-solid tests and radial injection, to prove the feasibility of such ignition. Sodium borohydride was used as the main catalyst, since it led to the best results.
The idea of a hypergolic ignition between a solid fuel and a liquid oxidizer was proven under different ambient conditions for various fuels. For the drop-on-solid tests, average ignition delay times at ambient conditions and under pressure, were always less than 10 ms, depending on the fuel and catalyst loading within the solid matrix. Using a hollow cylindrical fuel grain and radial injection, combustion delay times, i.e., the time between injection and complete burning of the fuel, were lower than 30 ms. This geometry allowed proper ignition of the fuel, as it contributed to mixing, flame expansion and buildup, while also simulating the inner port of a hypergolic hybrid motor.