Flame temperature diagnostics with water lines usingmid-infrared degenerate four-wave mixing

The feasibility of using degenerate four-wave mixing (DFWM) for hot gas thermometry in the mid-infrared spectral region is, for the first time, demonstrated by probing molecular ro-vibrational transitions of water. DFWM spectra of hot water were recorded in specially designed flames, providing a series of temperatures varying from 1000 to 1900 K and, the dramatic spectral structure variations were used as temperature indicator. The intensity ratios between two hot water line groups at around 3231 cm(-1) were especially studied and composed into a calibration table for flame temperature measurement using DFWM spectra. The saturation properties of different lines were also studied by recording the line intensity ratios as a function of laser power, and the results indicated that saturated excitation was in favor of reliable temperature measurements. As validation, infrared DFWM spectra in phi = 1.52 flat premixed methane/air flame were recorded, and a good temperature value was obtained. Moreover, the recently released HITEMP2010 database as well as its previous version HITEMP2000 were adopted to simulate the hot water spectra and to analyze the line intensity ratios. Copyright (C) 2011 John Wiley & Sons, Ltd.