Investigation of injector system and gas generator propellant for aft-injected hybrid propulsion

This research consisted of investigate a novel aft-injected hybrid (AIH) rocket propulsion system. An AM motor operates with the use of a fuel-rich solid propellant (gas generator) which is then mixed in a post combustion chamber with additional oxidizer. The first portion of this dissertation was focused on the development of the gas generator propellant. This included propellant ingredient selection through use of theoretical chemical equilibrium analysis. This was supplemented with mixing of propellant batches and hot-fire testing to obtain ballistic data. The final gas generator propellant used ammonium perchlorate as the oxidizer, HTPB, as the binder, and polyethylene as the fuel. It was discovered that below approximately 400-550 psi the gas generator propellant would self-extinguish, thereby providing the required safety aspects under ambient conditions. Three larger propellant batches with slight ingredient changes were mixed and casted so 4" diameter BATES grains could be hot-fire tested. The final selected propellant batch achieved a burn rate of 6.5 mm/s at 800 psi and was used for experimental injector testing in the sub-scale aft-injected motor. The second portion of this research was focused on the fabrication and experimental testing of a sub-scale aft-injected motor, specifically aimed at investigating the injector. This sub-scale motor used water as a substitute oxidizer in order to obtain temperature measurements in the post combustion chamber due to the cooler temperatures (≈ 890°C). This motor demonstrated the feasibility of the aft-injected concept, and six different injectors were tested. With this it was shown that the momentum ratio plays a significant role in determining how efficient the injector mixes the liquid and gas. To further supplement the injector research a numerical model was developed and presented.