Quantitative temperature measurements in high-pressure flames with multi-line nitric oxide (NO)-LIF thermometry
A versatile and accurate temp. measurement technique for steady, high-pressure flames is investigated using excitation wavelength-scanned laser induced fluorescence (LIF) within the NO A-X(0,0) band, and demonstration expts. are performed in premixed methane/air flames at pressures between 1 and 60bar with an equivalence ratio of 0.9. Excitation spectra are simulated with an efficient computational spectral simulation and fit to the exptl. data to ext. gas temp. The LIF scan range was chosen to provide sensitivity over a wide temp. range and minimize interference from oxygen. The fitting method is robust against elastic scattering and broadband LIF interference from other species, and yields abs., calibration-free temp. measurements. A NO addn. method is used to det. the intensity of background signals and simultaneously to det. nascent NO concn. in the post-flame gases. The NO-LIF temps. are in good agreement with intrusive single color pyrometry of a platinum/rhodium bead. The proposed thermometry method will provide a useful tool to study high-pressure flame chem. and also to evaluate fast-imaging thermometry techniques for practical diagnostics of high-pressure combustion systems.
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