Scale-up Tests of High Regression Rate Liquefying Hybrid Rocket Fuels

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 to 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 and the use of oxidizing additives or other regression rate enhancement schemes is not required. 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 hazardous components and can be shipped by commercial freight as a non-hazardous commodity. At the present time, grains up to 8.4 inches in diameter and 45 inches long are fabricated in a general-purpose laboratory at Stanford University. To further demonstrate the feasibility of this approach, a series of scale-up tests with gaseous oxygen have been carried out using a new Hybrid Combustion Facility (HCF) at NASA Ames Research Center. The data from these tests are in agreement with the small scale, low pressure and low mass flux laboratory tests at Stanford and confirm the high regression rate behavior of the fuels at chamber pressures and mass fluxes representative of commercial applications.