A revisit to the validity of flamelet assumptions in turbulent premixed combustion and implications for future research

Abstract

The flamelet assumption has been widely used for analysis and modeling of turbulent premixed flames over the past decades. Despite its popularity, validity of this assumption has been challenged originally by Borghi [1] in 1985. After Borghi [1], results of several research groups from, for example, the Universities of Toronto, Sydney, British Columbia, and Lund University showed that the reaction zone of turbulent premixed flames can in fact become relatively thick, disagreeing with the flamelet assumption. In contrast with the results of these research groups, those from, for example, the University of Michigan disagree and suggest the premixed flames reaction zone remains relatively thin. In this article, first, we compile the results from several different research groups and argue why turbulent premixed flames may in fact feature thick reaction zones, and what may be the underlying reason for existence of such discrepancy in the literature. Then, we aim to review two ongoing questions related to how fast turbulent premixed flames burn, and how this is related to the flamelet/non-flamelet behavior. It is reviewed that relaxing the flamelet assumption and considering that premixed flames can thicken allow to reconcile the difference between the local and global consumption speeds of turbulent premixed flames as well as to understand/model a premixed flame behavior, which is referred to as the bending behavior in the literature.