Near Wall Dynamics of Premixed Flames

Highly-resolved numerical simulations employing detailed reaction kinetics and molecular transport have been applied to flame-wall interaction (FWI) of laminar premixed flames. A multiple plane-jet flame (2D) has been considered, which is operated with premixed methane/air mixtures at atmospheric conditions and with different equivalence ratios. Free flame (FF) and side-wall quenching (SWQ) conditions have been accomplished by defining one lateral boundary as either a symmetry plane for FF or a cold wall with fixed temperature for SWQ. An equidistant grid with a resolution of 20 mu m is used to resolve the FWI zone. The GRI-3.0 mechanism is used for computing chemical reaction rates. The flame is tangentially compressed when approaching the cold wall, and elongated in the FF case, causing an inversion of the sign of the tangential strain rate Ka(s) and a considerable decrease of the total stretch rate K-a tot for the SWQ flame. The flame consumption speed S L decreases with decreasing normal stretch due to curvature K-c while approaching the cold wall, but it increases with decreasing Ka (c) for the FF case, leading to an inversion of the Markstein number Ma tot based on Ka tot from positive in FF to negative in the SWQ case. The results reveal a strong correlation of flame dynamics during transitions from FWI to freely propagating flames, which may bring a new perspective for modeling FWI phenomena by means of flame dynamics. To do this, the quenching effect of the wall may be reproduced by an inversion of the Markstein number from positive to negative in the FWI zone and applying the general linear Markstein correlation, leading to a decrease of the flame consumption speed. In addition, the quenching distance evaluated from S-L has been found to be almost equal to the unstretched laminar flame thickness, which compares quantitatively well with measured data from literature. (c) 2020 The Combustion Institute. Published by Elsevier Inc. All rights reserved.

Automated summary

Highly-resolved numerical simulations are used to study flame-wall interaction of laminar premixed flames, revealing changes in flame dynamics as the flame approaches a cold wall or operates as a free flame. The flame is compressed tangentially near the cold wall and elongated in the free flame case, leading to variations in flame consumption speed based on normal and tangential strain rates. This research provides new insights for modeling FWI phenomena and demonstrates a strong correlation of flame dynamics during transitions from FWI to freely propagating flames.