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 hy- droxyl (OH) radical around 306 nm in the plume of a hybrid rocket motor. Hydroxyl ter- minated polybutadiene (HTPB) was used as the fuel and gaseous oxygen as the oxidizer. The experimental spectra were analyzed by compari- son with known vibrational and rotational lines using a multi-parameter curve-fitting program. OH radical concentration and temperature pro- files of the rocket plume are presented along with details of the spectrometer specifications.