Experimental evaluation of strategies for quantitative laser-induced-fluorescence imaging of nitric oxide in high-pressure flames (1–60 bar)

Nitric oxide laser-induced-fluorescence (NO-LIF) 2-D imaging measurements using a new multi-spectral detection strategy are reported for high-pressure flames (1–60 bar). This work builds on previous research that identified interference LIF from O2 and CO2 in high-pressure flames and optimized the choice of excitation strategies as a function of application conditions. In this study, design rules are presented to optimize the LIF detection wavelengths for quantitative 2-D NO-LIF measurements over a wide range of pressures (1–60 bar) and temperatures. Simultaneous detection of LIF in multiple wavelength regions enables correction of the NO signal for interference from O2 and CO2 and allows simultaneous imaging of all three species. New experiments of wavelength-resolved 1-D LIF in slightly lean (ϕ = 0.9) and slightly rich (ϕ = 1.1) methane/air flames are used to evaluate the design rules and estimate the NO detection limits for a wide range of flame conditions. The quantitative 2-D measurements of NO in the burnt gas are compared with model calculations (using GRI-Mech 3.0) versus pressure for slightly lean and slightly rich flames. The discussions and demonstrations reported in this study provide a practical guideline for application of instantaneous 1-D or 2-D NO-LIF imaging strategies in high-pressure combustion systems.