Quantitative laser-saturated fluorescence measurements of nitric oxide in counter-flow diffusion flames under sooting oxy-fuel conditions

Abstract

We report quantitative, spatially resolved, laser-saturated fluorescence measurements of nitric oxide ([NO]) concentration in sooting, high-temperature, oxygen-methane, counter-flow diffusion flames at atmospheric pressure. Six different flames containing 1%, 3%, and 10% N2 in either the oxidizer or fuel streams are investigated at a global strain rate of 20 s−1. Excitation of NO is obtained at 224.45 nm in the γ(0,0) band and detection is performed in a 2-nm region centered at 235.78 nm in the γ(0,1) band. Numerical computations for all counter-flow diffusion flames are conducted using OPPDIF with GRI Mech-3.0. The effect of gas-phase radiation is considered in the modeling. Excitation scans indicate no significant change in background for oxygen-rich as compared to air-rich flames and detection scans verify the absence of interferences from other species. Quantitative axial profiles of [NO] are presented for all six flames. Comparisons with modeling indicate good agreement in those regions of each flame having predicted temperatures below 2600 K. Enhanced radiative heat loss caused by soot formation leads to poorer agreement between predicted and measured NO concentrations in regions at higher flame temperatures (T > 2600 K), thus indicating the need for a combined soot formation and radiation model.