Measurements and Prediction of Nitrogen Oxide Formation in Flickering Flames

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Abstract - Miller CTS - 9729578 A numerical model for a flickering, or time-varying, flame is developed; this model is intended to accurately and efficiently predict emission levels for nitrogen oxides. The model consists of three sections: (1) prediction of flame structure through solution of conservation equations in mass, momentum, energy, and mixture fraction; (2) application of a flamelet library approach to predict concentrations of carbon, hydrogen, and oxygen species; and (3) post-processing nitrogen chemistry to predict local levels and emissions of nitrogen oxide species. The unsteady flame structure is predicted using an adaptive spectral element discretization of the conservation equations on both serial and parallel machines. The existing incompressible spectral element code is revised to permit variable density. At each step in the process, model predictions are compared with measurements of concentration from tunable-diode laser absorption spectroscopy (TDLAS) on a methane-fueled flame, including in situ measurements of carbon monoxide, carbon dioxide, and methane and conditional sampling of the flame using a pulsed quartz microprobe to determine concentrations of trace nitrogen species including nitric oxide, nitrogen dioxide, ammonia, and hydrogen cyanide. This effort introduces a new computational approach for the modelling of pollutant formation and flame behavior.