Line-of-sight profiling of temperature and species in propellant flames using FTIR spectroscopy

The purpose of this work is to deduce line-of-sight variation of temperature and species concentrations in high-pressure, solid-propellant flames by using spectral transmittances acquired by Fourier transform infrared spectrometry. To deduce these variations, an inverse technique was implemented based on the Marquardt- Levenberg method. Two approaches were used to validate the inverse algorithm. First, the average temperature and species concentrations were determined of a series of calibration gases. Second, temperature and relative mole-fraction profiles within nitramine-composite propellant flames at low pressures were compared with similar measurements made by using fine-wire thermocouples and a micro-probe mass spectrometer. Having validated the data-reduction algorithm, it was applied to spectral transmittance data acquired for a highpressure, self-sustained solid-propellant flame. It was concluded that: 1) at about 3-4 mm above the surface, one must account for line-of-sight variations; 2) the deduced centerline temperatures agreed to within 50 K of those measured using fine-wire thermocouples; and 3) the deduced centerline concentrations of CO and NO established a dark-zone behavior which is expected of nitramine-composite propellant flames. However, to deduce the line-of-sight variation of other IR-active species, further improvements in the data base of the spectral absorption coefficients must be made