Diode laser atomic fluorescence temperature measurements in low-pressure flames

Temperature measurements have been performed in a low-pressure flame by the technique of diode laser induced atomic fluorescence. The experiments were done in a near-stoichiometric flat-flame of premixed methane, oxygen and nitrogen, at a pressure of 5.3 kPa. Indium atoms were seeded to the flame and probed using blue diode lasers; the lineshapes of the resulting fluorescence spectra were used to determine the flame temperature at a range of heights above the burner plate. The particular issues associated with the implementation of this measurement approach at low pressure are discussed, and it is shown to work especially well under these conditions. The atomic fluorescence lineshape thermometry technique is quicker to perform and requires less elaborate equipment than other methods that have previously been implemented in low-pressure flames, including OH-LIF and NO-LIF. There was sufficient indium present to perform measurements at all locations in the flame, including in the pre-heat zone close to the burner plate. Two sets I.S. Burns · C.F. Kaminski · J. Hult Department of Chemical Engineering, University of Cambridge, Pembroke Street, Cambridge CB2 3RA, UK Present address: I.S. Burns ( ) Department of Chemical and Process Engineering, University of Strathclyde, Montrose Street, Glasgow G1 1XJ, Scotland e-mail: [email protected] Fax: +44-141-5522302 N. Lamoureux · P. Desgroux PC2A Lille, UMR 8522, USTL, 59655 Villeneuve d’Ascq, France C.F. Kaminski SAOT School of Advanced Optical Technologies, Max Planck Research Group, Division III, Universität Erlangen-Nürnberg, Erlangen, Germany of temperature measurements have been independently performed by using two different diode lasers to probe two separate transitions in atomic indium. The good agreement between the two sets of data provides a validation of the technique. By comparing thermocouple profiles recorded with and without seeding of the flame, we demonstrate that any influence of seeding on the flame temperature is negligible. The overall uncertainty of the measurements reported here is estimated to be ±2.5% in the burnt gas region. PACS 42.55.Px · 32.50.+d · 42.62.Fi