Application of Hydroxyl (OH) Radical Ultraviolet Absorption Spectroscopy to Rocket Plumes

A spectrometer system was constructed for measurement of transient species in flames by absorption of ultraviolet radiation. The output of a xenon arc lamp was used as the source of radiation, which was focused through the flame and onto a monochromator equipped with an intensified silicon diode array detector. The system was used to measure absorption by hydroxyl (OH) radical around 306 nm in the plume of a hybrid rocket motor. Hydroxyl terminated polybutadiene (HTPB) was used as the fuel and gaseous oxygen as the oxidizer. The experimental spectra were analyzed by comparison with known vibrational and rotational lines using a multi-parameter curve-fitting program. OH radical concentration and temperature profiles of the rocket plume are presented along with details of the spectrometer specifications.