Experimental assessment and enhancement of planar laser-induced fluorescence measurements of nitric oxide in an inverse diffusion flame

We have experimentally assessed the quantitative nature of planar laser-induced fluorescence (PLIF) measurements of NO concentration in an atmospheric-pressure, laminar, inverse diffusion flame (IDF). The PLIF measurements were assessed relative to a two-dimensional array of separate laser-saturated fluorescence (LSF) measurements. Furthermore, we have proposed, demonstrated and evaluated several experimentally-based procedures for enhancing the quantitative nature of PLIF concentration images. Because these experimentally-based PLIF correction schemes require only the ability to make PLIF and LSF measurements, they produce a more broadly applicable PLIF diagnostic compared to numerically-based correction schemes. Prior to the PLIF assessment, we experimentally assessed the influence of interferences on both narrow-band and broad-band fluorescence measurements at atmospheric and high pressures. On this basis, optimum excitation and detection schemes were determined for the LSF and PLIF measurements. As a result, a new methodology has been established for excitation/filter selection for broad-band detection measurements. An LSF/PLIF optical-diagnostics facility and a unique axial IDF burner were developed for the PLIF assessment. We found that $\sim$84% of the uncorrected PLIF measurements were equivalent to the corresponding LSF measurements to within the uncertainty in the LSF measurements. Single-input and multiple-input, experimentally-based PLIF enhancement procedures were developed for application in test environments with both negligible and significant error gradients due to variations in the electronic quenching rate coefficient. A minimal-input procedure was also demonstrated which uses existing knowledge of the test environment to optimize the design of the correction procedure. Each experimentally-based procedure provides a $\sim$50% enhancement in the quantitative nature of the PLIF measurements, and results in concentration images that are nominally as quantitative as a single LSF point measurement. Furthermore, these experimentally-based PLIF correction procedures can be applied to other species, including radicals, for which no experimental data are available from which to implement numerically-based PLIF enhancement procedures