Regression-Rate and Heat-Transfer Correlations for Hybrid Rocket Combustion

Abstract

A series of static engine Ž rings, 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, instantaneousregression rates. A dataanalysisprogramwas developedto help correlate the experimental data. The semi-empirical regression-rate correlation showed that, in addition to convection, radiation from soot and variable  uid properties across the boundary layer had signiŽ cant effects on regressionrate behavior. The radiant heat  ux from sootwas relativelymore signiŽ cant under lowmass  ux and low oxidizerto-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 § 3%. Stantonand Nusselt-number correlations were also developed and found to depend on both  ow regime and radiant heat  ux. 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.