Temperature measurements in gases by use of planar laser-induced fluorescence imaging of NO.

Two techniques based on planar laser-induced fluorescence of NO are applied to the measurement of two-dimensional temperature fields in gaseous flows. In the single-line technique, the NO fluorescence signal, which is in general a function of temperature, pressure, and mole fraction, can be reduced to a function of temperature alone. In this limit, a single measurement of fluorescence can be directly related to temperature. In contrast, in the two-line thermometry technique the ratio of fluorescence signals resulting from excitation of two different rovibronic states is related to the fractional populations in the initial states, which are solely a function of temperature. The one-line method is applied to the study of a laminar heated jet, and the two-line technique is used to measure temperature in a supersonic underexpanded jet. In addition, energy transfer in NO laser-induced fluorescence is analyzed with multilevel rate equation models. Finally, an accurate model is developed for prediction of the temperature dependence of the NO fluorescence signal.