The hybrid rocket concept has been around for more than seventy-five years. The idea is to store the oxidizer as a liquid and the fuel as a solid producing a design that is immune to large-scale chemical explosion. The fuel is contained within the combustion chamber in the form of a cylinder with one or more channels called ports hollowed out along its axis. Combustion takes place between vaporized oxidizer flowing through the ports and fuel evaporating from the solid surface.
While the hybrid rocket enjoys many safety and environmental advantages over conventional systems, large hybrid rockets have not been commercially viable. The reason is that traditional systems use polymeric fuels that evaporate too slowly making it difficult to produce the high thrust needed for most applications. To compensate, the surface area for burning must be increased, and as the size of a hybrid rocket increases the number of required ports also increases leading to poor volumetric loading and poor fuel structural characteristics.
Recent research at Stanford University has led to the development of a class of paraffin-based fuels that burn at surface regression rates that are several times that of conventional polymeric fuels. These new fuels form a thin, hydro-dynamically unstable liquid layer on the melting surface of the fuel grain. Entrainment of droplets from the liquid-gas interface can substantially increase the rate of fuel mass transfer leading to much higher surface regression rates than can be achieved with conventional polymeric fuels. This permits the design of a high volumetric loading single-port hybrid rocket system with a density impulse comparable to a conventional hydrocarbon fueled liquid rocket propulsion system. Since the start of this work more than 800 tests have been carried out using a variety of oxidizers including LOx, GOx and Nitrous Oxide.
Dr. Cantwell will show the analysis and performance of these fast burning systems along with comparisons with conventional solid and liquid systems.