A method for performing high accuracy temperature measurements in low-pressure sooting flames using two-line atomic fluorescence

We demonstrate a step change in the capability of diode laser excited two-line atomic fluorescence (TLAF) thermometry and show it is well-suited to the study of low-pressure sooting flames. The new developments to the technique reported here were essential to achieve the accuracy (+/-41 K) and precision (+/-8 K) required for useful measurements in such systems. This represents the first application of TLAF thermometry to the investigation of low-pressure sooting flames, an environment in which other thermometry techniques perform poorly. We thus demonstrate a practical application of diode laser TLAF to a burner that is the subject of a coordinated experimental and computational investigation of soot formation. The TLAF technique requires no calibration measurement and is compact and economical to set up in comparison with traditional laser thermometry methods. Temperature profiles were recorded in a laminar flat-flame operating on O-2, N-2 and CH4 at fuel equivalence ratio of 2.32 and pressures ranging from 18.7 to 26.7 kPa. Almost identical temperature profiles were observed at different pressures despite the fact that soot volume fractions changed by more than an order of magnitude between the lowest and highest operating pressures. The data will contribute to modelling efforts to understand the surprisingly strong dependence of soot volume fraction on pressure that has previously been observed under the range of conditions studied here and will be included in an openly available database on this flame, which includes species profile measurements obtained by other methods. In the current contribution we emphasise the technical implementation of diode TLAF as a new temperature diagnostic with near optimal characteristics for the study of low pressure, sooting flames. (C) 2010 The Combustion Institute. Published by Elsevier Inc. All rights reserved.