To successfully build a rocket engine with variable thrust you must devise a reliable and robust oxidizer flow control system. The goal of this thesis is to contribute to the goal of building a variable thrust (throttled) hybrid rocket engine, which could eventually be used to power scientific sounding rockets. A variable thrust hybrid engine would increase reusability, flexibility, and capability of almost any small rocket.
Specifically, this thesis work regards the development of the closed loop oxidizer flow control system. To do this, a small test rig was built in the lab that consists of all the components in an actual rocket engine except for the combustion chamber. Using this apparatus the behavior of water in the system was analyzed, including the characterization of the oxidizer flow control valve and the response of the system to various controller parameters. By having a process perfected for characterizing a system with water it makes the process much easier when done with the more exotic oxidizer materials such as nitrous oxide and carbon dioxide.
Saindon, Luke, "Development of Oxidizer Flow Control for use in Hybrid Rocket Motors of the Scientific Sounding Rocket Scale" (2012). Honors College. 33.