Regression and combustion characteristics of boron containing fuels for solid fuel ramjets

Abstract

A windowed, two-dimensional solid-fuel-ramjet motor was used with high-speed motion picture cameras to study the effects of fuel composition, pressure, and air mass flux on the surface behavior of metallized fuels within both the recirculation and boundary-layer combustion regions. Surface behavior and near-surface combustion characteristics were examined to help explain the regression rate/performance characteristics observed in actual motor hardware. Fuels containing no combustion catalyst exhibited the characteristic of extending the combustion envelope to lower pressures with lower values of Shore A hardness. Ignition/flammability limits appeared to be a strong function of surface pyrolysis within the recirculation region. Most metallized fuels exhibited shedding of flakes of (unburned) material from the fuel surface. Flake thickness for boron fuels was typically 200 /*, independent of pressure, and surface areas varied from less than 1 mm2 to approximately 22 mm2. The mass losses attributable to the flaking process play a major role in the overall fuel mass loss mechanism. Bimetallic fuels and fuels containing a combustion catalyst apparently had surface reactions which increase the surface temperature. This should be beneficial for obtaining more complete combustion of the metals within the motor.