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Effects of pressure and Karlovitz number on the turbulence-flame interactions in lean premixed H2/air flames

Wang, X; Jin, T; Xie, Y; Luo, KH; (2018) Effects of pressure and Karlovitz number on the turbulence-flame interactions in lean premixed H2/air flames. Fuel , 234 pp. 1293-1300. 10.1016/j.fuel.2018.07.158. Green open access

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Abstract

This paper presents three-dimensional direct numerical simulations of lean premixed turbulent H2/air flames in the thin and distributed reaction zones, with the Karlovitz numbers at 60, 110, 150 and 1000, and pressures at 1 and 5 atm, respectively. Flame front structures and chemical pathways are examined in detail to investigate the effects of pressure and turbulence on flames. There is an increasing number of finer structures on the flame front with increased Karlovitz number. Eddy structures are observed downstream of the reaction zone under high turbulence intensity and thus Karlovitz number, indicating that the turbulent eddies are small and energetic enough to break through the distributed reaction zone. Statistical analysis indicates that the probability of high curvatures increases with increasing Karlovitz number at a constant pressure. When the Karlovitz number is kept constant, the probability of high curvatures is significantly higher at the atmospheric pressure than at elevated pressure. The approximation of Schmidt number (Sc = 1) in theoretical analysis introduces errors in the estimation of the smallest flow scale and the Karlovitz number. Accordingly, in the turbulent flame regime diagram, the boundary between the thin reaction zone and the distributed reaction zone should be modified at the elevated pressure. Moreover, the decorrelation of heat release and H2consumption is directly related to turbulence intensity, and the decorrelation is reduced at the elevated pressure. Due to the enhanced radical transport at high Karlovitz number, chemical pathways can be locally changed, which is more significant at elevated pressure.

Type: Article
Title: Effects of pressure and Karlovitz number on the turbulence-flame interactions in lean premixed H2/air flames
Open access status: An open access version is available from UCL Discovery
DOI: 10.1016/j.fuel.2018.07.158
Publisher version: http://dx.doi.org/10.1016/j.fuel.2018.07.158
Language: English
Additional information: © 2018 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY license
Keywords: Premixed turbulent flame, Elevated pressure, Turbulence intensity, Flame front structure, Chemical pathway
UCL classification: UCL > Provost and Vice Provost Offices
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Engineering Science
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Engineering Science > Dept of Mechanical Engineering
URI: https://discovery.ucl.ac.uk/id/eprint/10054560
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