Turbulence effects on the chemical pathways for premixed methane/air flames

This paper investigates the influence of turbulence-chemistry interactions on kinetic pathways in turbulent premixed CH4-air flames. It compares the relative roles of the different reactions in CH4 oxidation to laminar flame models, and assesses the degree to which these interactions alter the well-established oxidation pathway in laminar flames. This is accomplished by utilizing the turbulent lean (ϕ = 0.7), CH4-air flame DNS database from Aspden et al. (Combust. Flame 166 (2016) 266–283). The roles of dominant reactions to heat release and radical formation/consumption are analyzed with increasing turbulence and compared with stretched flame calculations from counterflow flames and perfectly stirred reactors. The turbulent DNS results show relatively little change in the fractional contributions toward heat release or key species’ consumption/production over the Ka=1-36 range, when averaged over the entire flame. In contrast, the laminar results show some sensitivity to stretch, although this sensitivity is not large for the dominant reactions. These fractional contributions for the turbulent flames are quite similar to laminar stretched flame calculations, when averaged over the entire flame. Larger changes are observed in reactions of secondary importance, or when looking at more localized measures. For example, negatively curved elements show a different dominant heat release reaction compared to overall flame chemistry. These results suggest that kinetic mechanisms that are optimized using laminar flame targets can adequately describe turbulence-chemistry interactions under in the presence of significant turbulent intensity