This Is AuburnElectronic Theses and Dissertations

Development of a Two Dimensional, Optically Accessible, Hybrid Rocket Motor




Boyle, Sadie

Type of Degree

Master's Thesis


Aerospace Engineering


Traditionally, launch vehicles and in-space vehicles use solid rocket motors (SRM) and liquid rocket engines (LRE) to propel them into and through space. However, there are many drawbacks to both propulsion systems. Hybrid rocket motors (HRM) present a viable alternative and have many advantages over LREs and SRMs as they are safe, simple, comparatively lower cost, have a relatively high specific impulse, and have relight and throttle capabilities. This unique combination of qualities makes HRMs a desirable propulsion choice for launch vehicle upper stages, sounding rockets, boosters, tactical systems, and in-space applications. However, during the development of any new high pressure combustion system, combustion instabilities are likely to occur. HRMs have four unique mechanisms that drive combustion instabilities. The four mechanisms that lead to combustion instabilities in hybrids are (1) oxidizer vaporization, (2) chuffing, (3) pressure coupled regression, and (4) vortex shedding. This study focuses on the design, development, and testing of a two dimensional, optically accessible, HRM. This thesis outlines the importance of HRMs, the history and previous studies, the design and safety of the HRM, and the initial testing conducted. The initial testing consisted of looking at how the hybrid rocket motor performed using hydroxyl-terminated polybutadiene (HTPB) and high-density polyethylene fuels (HDPE) as well as 0.05 inch, 0.07 inch, and 0.08 inch oxidizer injector diameters. Higher pressures earlier in the burn were seen during the tests that used HTPB as the fuel compared to the tests that used HDPE as the fuel. The burn became more stable with increased oxidizer injector diameters and the burn time decreased with increasing oxidizer injector diameter. This process resulted in a test bed that will allow the Auburn University Combustion Physics Lab to conduct further research. The hope is that in future studies this HRM can be used to investigate vortex shedding as a driving mechanism for combustion instabilities.