Solid propellant combustion zone structure from analysis of hydroxylradical chemiluminescence

Hydroxyl radical Chemiluminescence spectra have been obtained in the combustion zone above ammonium perchlorate composite solid propellant burning at multiatmospheric pressures in a laboratory scale strand burner. These semiresolved (.13 nm) spectra were analyzed by constructing OH synthetic spectra and employing a best-fit technique to determine the rotational temperature and vibrational population distribution in the A!, electronic state of OH in the flame. Values for rotational temperature and vibrational population distribution were obtained for pressures from 0.2 to 7.0 MPa at three positions above the propellant surface. Quantitative comparison of results over a range of pressures for a given spatial position is mitigated by the potentially significant effects of self absorption on the measured spectra. Comparisons at a given pressure for various positions above the propellant surface should not be affected by self-absorption, and show a fairly constant rotational temperature and vibrational population distribution from near the surface out to the maximum position investigated (12 mm). These results indicate that a chemical combustion environment involving short lived radical species exists at distances very far from the propellant surface even at elevated pressures. Interpretation of the spectral characteristics of the emission data also indicates highly nonequilibrium vibrational populations and possible non-Boltzmann rotational distributions which increasingly diverge from equilibrated distributions with increasing pressure.