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

A series of static engine firings, thermal pyrolysis experiments, and gas c hromatograph/mass spectrometer tests were conducted to investigate the soli d-fuel regression rate and heat-transfer behavior in a lab-scale hybrid roc ket motor burning hydroxyl terminated polybutadiene/gaseous oxygen. A real- time, X-ray radiography system was used to determine the local, instantaneo us regression rates. A data analysis program was developed to help correlat e the experimental data. The semi-empirical regression-rate correlation sho wed 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 signifi cant under low mass flux and low oxidizer-to-fuel ratio conditions. Radiati on from CO2, H2O, and CO was quite small compared to convection and soot ra diation. The nondimensional regression-rate correlation agreed with the exp erimental data to within +/-13%. Stanton- and Nusselt-number correlations w ere 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 reasona ble accuracy.