Global pathway analysis of the extinction and re-ignition of a turbulent non-premixed flame

In the present work, Global Pathway Analysis (GPA) is applied to understand the direct numerical simulation (DNS) data of a 3D turbulent non-premixed syngas/air flame using two different chemical kinetics models, GRI-Mech 3.0 (GRI) and an 11-species syngas model (SKE). This complicated reacting system is analyzed based on several Global Pathways identified by GPA to describe the oxidization process from H₂ to H₂O. GPA finds that GRI contains a major Global Pathway through H₂O₂, which is missing in SKE. In addition, for the major Global Pathways shared by the two models, GRI predicts larger net radical production. These two findings together explain why GRI predicts less local extinction and more reignition. Conditional statistics show that high temperature pathways have significantly higher net radical production rate than low temperature pathways, indicating that the former ones are dominant. Based on the analysis of conversion steps and elementary reactions, it is found that at the same spatial location, the reasons of larger net radical production in GRI could be different at different times. Finally, the scattering plots indicate that turbulence can significantly enhance the low temperature pathways, which makes the DNS data significantly deviating from the 1D steady state solutions.