Temperature measurement in flames using TLAF, alkali emission and OH UV absorption

Abstract: There is a continued need for reliable and convenient nonintrusive thermometric techniques for better understanding and effective control of combustion related processes. In this thesis, three spectroscopic thermometric methods were studied to evaluate the hot flue gas temperatures provided by a multi-jet burner. These methods include the two-line atomic fluorescence (TLAF) thermometry, the Na/K two-line emission method, and the thermometry using OH absorption spectroscopy. The temperature distribution along the long-side of the burner was measured using the TLAF method with an estimated uncertainty of ± 50 K. The emission intensity ratios between the Na 589 nm and the K 766 nm lines were investigated, which showed strong temperature dependence at lean flames with an excess oxygen content higher than 2.2%. The emission intensity ratios between the K 404 nm and 766 nm spectral lines were also investigated and found to be strongly dependent on the OH concentration instead of the temperature due to the effect of chemi-excitation. The feasibility of thermometry using OH absorption spectrum was studied by two spectral fitting methods: the direct fitting method and the second derivative fitting method. Both methods were able to evaluate the temperature within an accuracy of 60 K, while the latter method provided better accuracy due to the proper elimination of the baseline deviations. A comparison of the three thermometric methods was discussed in the end.