Scale-Up Tests of High Regression Rate Paraffin-Based 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 three to four times that of conventional hybrid fuels. The approach involves the use of materials that form a thin, hydrodynamically unstable liquid layer on the melting surface of the fuel. Entrainment of droplets from the liquid-gas interface substantially increases the rate of fuel mass transfer, leading to much higher surface regression rates than can be achieved with conventional polymeric fuels. Thus, 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 multiport 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 nonhazardous commodity. At the present time, grains up to 0.19 m [19.1 cm (7.5 in.)] in diameter and 1.14 m [114.8 cm (45.2 in.)] 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. Data from these tests are in agreement with the small-scale, low-pressure, and low mass flux laboratory tests at Stanford University and confirm the high regression rate behavior of the fuels at chamber pressures and mass fluxes representative of commercial applications.