| Practical diagnostic strategies for detection of temperature and nitric oxide (NO) in high pressure (p<60bar) combustion systems using Laser-Induced-Fluorescence (LIF) of nitric oxide are investigated. NO-LIF, when applied to elevated pressures, suffers from a decrease of signal due to pressure broadening and attenuation of the propagating laser beam/fluorescence signals. In addition, overlapping of neighboring excitation lines and interference from LIF of other species (mainly O2 and CO2) can significantly influence the overall signal. The main purpose of this study is to investigate NO-LIF strategies which minimize the impact of these complications or allow for correction of their effects. A comprehensive study of NO-LIF in a laboratory high-pressure flame was carried out for various flame stoichiometries, pressures and excitation wavelengths to develop optimized excitation and detection strategies for high-pressure applications. Four main issues are addressed in this study. First, optimized excitation strategies are investigated for high-pressure applications in the A2Sigma+ - X2pi (0,0), (0,1) and (0,2) bands of NO. Second, CO2-LIF is identified as a major source of interference in the detection of NO-LIF in high-pressure combustion systems involving hydrocarbon chemistry. Third, an accurate multi-line thermometry technique for steady, high-pressure flames is proposed by fitting wavelength-scanned NO-LIF with computational simulations. Finally, measurements optimizing the detection strategies of 2-D NO-LIF imaging in high-pressure flames are reported. The discussion and demonstrations reported in this study provide a practical guideline for application of instantaneous 1-D or 2-D NO-LIF imaging in high-pressure combustion systems. |
