Abstract:

Recent research at Stanford University has led to the identification of a class of paraffin-based fuels that burn at surface regression rates that are 3-4 times that of conventional hybrid fuels. The approach involves the use of materials that form a thin, hydro-dynamically unstable liquid layer on the melting surface of the fuel. 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. Thus a high regression rate is a natural attribute of the fuel material avoiding the need for oxidizing additives or other regression rate enhancement schemes. The fuels provide specific impulse performance comparable to kerosene but are approximately 20% more dense than kerosene. This permits the design of a high volumetric loading single-port hybrid system with a density impulse comparable to or greater than a hydrocarbon fueled liquid system. The high regression rate hybrid removes the need for a complex multi-port grain and most applications up to large boosters can be designed with a single port configuration. The fuel contains no toxic or oxidizing components and can be shipped by commercial freight as a non-hazardous commodity. To further demonstrate the feasibility of this approach, a series of scale-up tests using several oxidizers including gaseous Oxygen, Liquid Oxygen and Nitrous Oxide have been carried out on intermediate scale motors. The data from these tests are in agreement with small scale, low pressure and low mass flux laboratory tests and confirm the high regression rate behavior of the fuels at chamber pressures and mass fluxes representative of commercial applications.