摘要:

Filtered Rayleigh Scattering (FRS) has been investigated to determine the feasibility of the technique to obtain instantaneous two-dimensional temperature measurements in reacting flows. The laser frequency, of an injection seeded Nd:YAG laser, is tuned to an absorption line of iodine which is contained in an optical cell. The iodine filter is placed in front of an intensified CCD camera recording the scattered light. Background scattering from solid surfaces and particles is strongly absorbed by the iodine, while much of the Doppler broadened Rayleigh scattering is transmitted by the filter. The gas temperature can then be deduced from the measured transmission of the molecular Rayleigh scattering. Two different premixed flames were investigated, a hydrogen-air flame created using a Hencken burner and a methane-air flame. The accuracy of the FRS measurements was investigated by comparing FRS-derived temperatures with calculated values and temperatures recorded with coherent anti-Stokes Raman spectroscopy. For the hydrogen-air flames, the FRS method gave temperatures within 2% of the expected value (from measurement and/or calculation). Methane-air flames were investigated to demonstrate the effectiveness of FRS to measure temperatures near surfaces (within 300 μm) and to obtain “large field” two-dimensional temperature information in a buoyantly driven flame. A detailed uncertainty analyses is provided to show the strengths and limitations of the FRS technique for temperature measurements in reacting flows.

ISSN:0010-2202    

DOI:10.1080/00102209708935663

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Previous planar imaging measurements in lifted, turbulent jet flames provide evidence for the three-dimensionality of these flows and the importance of flame propagation in the azimuthal direction normal to the image plane. The primary objective of the present paper is to obtain data in a plane normal to the flow direction that will provide a better understanding of the three-dimensional features of the flow. In addition, the results of the previous measurements were limited to a Reynolds number of 7,000. imaging data at a Reynolds number of 12,100 will be presented to extend the previous findings to a higher Reynolds number regime. Images of the radial cross section in the low Reynolds number flame show that considerable asymmetry and structure exist. At upstream locations, the flame is typically not continuous around the circumference of the jet but consists of multiple flame segments. Farther downstream, the flame extends over a larger percentage of the circumference with breaks confined to smaller lengths along the circumference. The CH chemiluminescence images show numerous breaks in the flame sheet. These breaks coincide with outward bulges in the flame sheet that result from the formation of vortical structures in the jet shear layer. The images clearly show the three-dimensionality of the flow, since the breaks in the flame are localized to the area of the bulges and do not extend around the circumference of the central jet. Many of the same features found in the lower Reynolds number flame are also seen at the higher Reynolds number. Consistent with the larger turbulence scales existing farther downstream where this flame is stabilized, the flame surface is more convoluted and breaks in the flame sheet are more extensive. Rapid discontinuous jumps upstream by the flame are seen considerably more often than in the lower Reynolds number flame, which is indicative of the higher turbulence levels and greater three dimensionality of this flame.

ISSN:0010-2202    

DOI:10.1080/00102209708935664

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor