On the ambiguity of premixed flame thickness definition of highly pre-heated mixtures and its implication on turbulent combustion regimes

Abstract

Freely propagating, one-dimensional, laminar, premixed flames of ethylene–air are analysed at standard temperature and pressure (STP) and at elevated temperature and pressure conditions to reveal the differences in flame structure. For high-temperature and low-pressure conditions, there is a significant contribution to the total heat release in the post-flame region leading to an ambiguity in the definition of the characteristic flame structure thickness. The potential implications on the identification of the appropriate turbulent flame regime in Borghi or Re-Da regime diagrams are highlighted. The contributions of individual reactions to the total heat release across the entire flame structure are analysed to understand the impact of turbulence–chemistry interactions.

Keywords:

• Laminar premixed flame structure
• high-temperature combustion
• heat release structure
• turbulent combustion regimes
• ethylene–air flames

Disclosure statement

No potential conflict of interest was reported by the author(s).

Supplemental data

Supplemental data for this article can be accessed at https://doi.org/10.1080/13647830.2020.1722857.

Notes

1 Flame structure analysis of hydrogen–air mixtures were also performed using the H${}_2$ kinetic model of Burke et al. [23] (13 species and 27 reactions) and results are given as Supplementary Material (S.2). The discussion focuses on the ethylene–air mixtures due to its increased relevance to real fuel combustion.

Additional information

Funding

This work was supported by the National Science Foundation [grant number NSF-1511791]; Air Force Office of Scientific Research [grant number FAA FA9550-15-1-0440], with Dr Song-Charng Kong and Dr Chiping Li as Technical Monitors.