Line-of-Sight Variations of Temperature and Species in Solid Propellant Flames

The purpose of this work is to deduce line-of-sight variations 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 developed. For its validation, temperature and mole-fraction profiles within nitramine-composite propellant flames at low pressures were compared with similar measurements made by using fine-wire thermocouples and a microprobe mass spectrometer. Subsequently, it was applied to spectral transmittance data acquired for a high-pressure, self-sustained solid-propellant flame. Several conclusions were made. First, at about 3-4 mm above the surface, one must account for line-of-sight variations. Second, the deduced centerline temperatures were within 50 K of those measured using fine-wire thermocouples. Finally, 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 infrared-active species, further improvements in the database of the spectral absorption coefficients must be made.