Quantitative temperature measurements in high-pressure flames with multi-line nitric oxide (NO)-LIF thermometry
A versatile and accurate temperature 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 experiments 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 (LIFSim) and fit to the experimental data to extract gas temperature. The LIF scan range was chosen to provide sensitivity over a wide temperature range and minimize interference from oxygen. The fitting method is robust against elastic scattering and broadband LIF interference from other species, and yields absolute, calibration-free temperature measurements. A NO addition method is used to determine the intensity of background signals and simultaneously to determine nascent NO concentration in the post-flame gases. The NO-LIF temperatures 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 chemistry and also to evaluate fast-imaging thermometry techniques for practical diagnostics of high-pressure combustion systems.
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