Diagnostics and Modeling of Stagnation Flames for the Validation of Thermochemical Combustion Models for NO_<i>x</i> Predictions

Abstract

This article presents a combined experimental and modeling approach for the study of NO formation in premixed stagnation flames. In the experiments, one-dimensional (1-D) Particle Image Velocimetry (PIV), 1-D spectrally resolved Planar Laser-Induced Fluorescence (PLIF), and 1-D NO-LIF thermometry are used to measure high resolution profiles, which are directly compared to numerical simulations. The simulations are performed with Cantera using 1-D hydrodynamics, transport, and detailed thermochemical models. Accurate measurements of premixed gas composition, gas velocity, temperature, and spread rate yield all necessary inlet boundary conditions. Use of a temperature-controlled stagnation plate allows for first-order heat loss effects to be imposed on the numerical simulation, rather than relying on external temperature corrections. The experiments provide a sensitive test of NO formation, result in multiple validation targets which do not rely on extrapolations, and allow for accurate specification of measurement uncertainties when comparing experiments to simulations. This article provides a discussion of the diagnostic techniques and compares experimental results for methane–air flames to numerical predictions using a number of natural gas thermochemical models (GRI-Mech 3.0, GDF-Kin 3.0, CRECK 1212, and Konnov 0.6) and their associated submodels for NOx formation. The reported results indicate that further adjustments to thermochemical combustion models are needed to accurately predict NOx pollutant formation in small hydrocarbons under atmospheric-pressure conditions.