Regression-rate and heat-transfer correlations for hybrid rocket combustion

A series of static engine firings, thermal pyrolysis experiments, and gas chromatograph/mass spectrometer tests were conducted to investigate the solid-fuel regression rate and heat-transfer behavior in a lab-scale hybrid rocket motor burning hydroxyl terminated polybutadiene/gaseous oxygen. A real-time, X-ray radiography system was used to determine the local, instantaneous regression rates. A data analysis program was developed to help correlate the experimental data. The semi-empirical regression-rate correlation showed that, in addition to convection, radiation from soot and variable fluid properties across the boundary Layer had significant effects on regression-rate behavior. The radiant heat flux from soot was relatively more significant under low mass flux and low oxidizer-to-fuel ratio conditions. Radiation from CO2, H2O, and CO was quite small compared to convection and soot radiation. The nondimensional regression-rate correlation agreed with the experimental data to within +/-13%. Stanton- and Nusselt-number correlations were also developed and found to depend on both how regime and radiant heat flux, The regression-rate correlations predicted independent data from both a lab-scale tube burner and the 11-in. (28 cm) JIRAD motor to very reasonable accuracy.