Laser-induced fluorescence measurements and modeling of nitric oxide in counterflow partially premixed flames

Abstract

Quantitative measurements of NO concentration ([NO]) have been obtained along the centerline of atmospheric pressure, methane–air, counterflow partially premixed flames using the laser-induced fluorescence (LIF) technique. The effect of partial premixing was studied by investigating flames with fuel-side equivalence ratios (φ B) of 1.45, 1.6, 1.8, and 2.0 at a constant global strain rate near 20 s −1. Linear LIF measurements of [NO] are corrected for variations in the electronic quenching rate coefficient by using major species profiles generated by an opposed-flow flame code and quenching cross-sections for NO available from the literature. Corrected linear LIF measurements of [NO] and temperatures measured using thin filament pyrometry are compared with numerical predictions from the opposed-flow flame code by utilizing the GRI (version 2.11) mechanism for the NO kinetics. The effect of radiative heat loss on code predictions is accounted for by using an optically thin radiation model. Reasonably good agreement exists between LIF [NO] measurements and predictions in all flames. In particular, all predictions fall within 10% of measurements at peak [NO] locations. Spatial separation was observed between regions where prompt-NO and thermal-NO dominate in the φ B = 1.45 flame. A previously modified rate coefficient for the prompt-NO initiation reaction improved agreement between predictions and measurements in the region dominated by prompt NO.