Prediction of flame structure and pollutant formation of Sandia flame D using Large Eddy Simulation with direct integration of chemical kinetics

Large Eddy Simulation (LES) with direct integration of reduced chemical kinetics including NO chemistry is performed on the Sandia flame D. This approach allows a detailed analysis of the flame structure and pollutant formation. The Analytically Reduced Chemistries (ARCs) are obtained using Directed Relation Graph method with Error Propagation (DRGEP) and Quasi-Steady-State (QSS) approximation. Two ARCs containing both 22 species are derived for methane-air oxidation, from GRI 2.11 and GRI 3.0 detailed mechanisms. They correctly predict fuel consumption speed, as well as NO and CO concentrations in laminar premixed and non-premixed flames at atmospheric conditions. It is found that the NO production strongly depends on the detailed mechanism, being significantly higher with GRI 3.0 in rich premixed flames and in diffusion flames. The two ARCs are then used in highly-resolved LES of the Sandia flame D. The numerical results are in very good agreement with the experiment in terms of aerodynamics, mixture fraction and temperature profiles. The CO concentration is also well predicted with the two ARCs. For NO, a satisfactory agreement with the measurements is obtained with the ARC based on GRI 2.11, while a significant over-prediction is obtained with the GRI 3.0-based ARC, consistently with the differences observed in laminar cases between the two GRI versions. A detailed investigation of the flame structure including a comparison with reference laminar flames reveals that the flame structure is essentially non premixed. The presence of the pilot jet alters the mixing process, leading to a flame structure that falls between two extreme non-premixed combustion regimes corresponding to the interaction of the rich central jet with either the hot gases from the pilot, or the coflow of fresh air. The associated laminar diffusion flamelets indicate that this particular flame structure influences the formation of pollutants, with a strong impact on CO production. (C) 2017 The Combustion Institute. Published by Elsevier Inc. All rights reserved.