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LES/PDF modeling of swirl-stabilized non-premixed methane/air flames with local extinction and re-ignition

Yu, S. LU ; Liu, X. LU ; Bai, X. S. LU ; Elbaz, A. M. and Roberts, W. L. (2020) In Combustion and Flame 219. p.102-119
Abstract

Turbulent non-premixed flames with local extinction and re-ignition exhibit multiple combustion modes including ignition waves, diffusion flames, partially premixed flames, and ignition-assisted partially premixed flames. The mechanisms of local extinction and re-ignition are not well understood and numerical modeling of multi-mode combustion is a challenging task. In this work, a specially designed swirl-burner was used to study local extinction and re-ignition of non-premixed turbulent methane/air flames. High speed Particle Image Velocimetry (PIV) and laser induced fluorescence of OH radicals (OH-PLIF) measurements along with Large Eddy Simulation (LES) were carried out to investigate the mechanisms of extinction and re-ignition... (More)

Turbulent non-premixed flames with local extinction and re-ignition exhibit multiple combustion modes including ignition waves, diffusion flames, partially premixed flames, and ignition-assisted partially premixed flames. The mechanisms of local extinction and re-ignition are not well understood and numerical modeling of multi-mode combustion is a challenging task. In this work, a specially designed swirl-burner was used to study local extinction and re-ignition of non-premixed turbulent methane/air flames. High speed Particle Image Velocimetry (PIV) and laser induced fluorescence of OH radicals (OH-PLIF) measurements along with Large Eddy Simulation (LES) were carried out to investigate the mechanisms of extinction and re-ignition processes in the burner. LES is based on a transported probability density function model within the framework of Eulerian Stochastic Fields (PDF-ESF). It is found that local extinction occurs when the scalar dissipation rate around the stoichiometric mixture fraction is high. The characteristic time scale for local extinction and re-ignition in the present flames is an order of magnitude longer than the characteristic time scale of diffusion/extinction of laminar flamelets. There are two mechanisms for flame hole re-ignition in the present flames. First, under low degree of local extinction conditions (i.e., for small flame holes surrounded by flames) the flame hole re-ignition is due to the mechanism of turbulent flame folding. Second, under high degree of extinction conditions (i.e., with large regions of extinction and lifted flames), re-ignition of the locally extinguished flame is due to the mechanism of ignition assisted partially premixed flame propagation. The results show that the PDF-ESF model is capable of simulating the quenching and re-ignition process found in the experiments.

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author
organization
publishing date
type
Contribution to journal
publication status
published
subject
keywords
LES, Local extinction, Non-premixed swirl flames, PDF-ESF, Re-ignition
in
Combustion and Flame
volume
219
pages
18 pages
publisher
Elsevier
external identifiers
  • scopus:85086085878
ISSN
0010-2180
DOI
10.1016/j.combustflame.2020.05.018
language
English
LU publication?
yes
id
3a7b5a69-fdd0-4b46-9c4a-64adbd04b81a
date added to LUP
2020-06-30 10:09:04
date last changed
2020-07-01 05:34:51
@article{3a7b5a69-fdd0-4b46-9c4a-64adbd04b81a,
  abstract     = {<p>Turbulent non-premixed flames with local extinction and re-ignition exhibit multiple combustion modes including ignition waves, diffusion flames, partially premixed flames, and ignition-assisted partially premixed flames. The mechanisms of local extinction and re-ignition are not well understood and numerical modeling of multi-mode combustion is a challenging task. In this work, a specially designed swirl-burner was used to study local extinction and re-ignition of non-premixed turbulent methane/air flames. High speed Particle Image Velocimetry (PIV) and laser induced fluorescence of OH radicals (OH-PLIF) measurements along with Large Eddy Simulation (LES) were carried out to investigate the mechanisms of extinction and re-ignition processes in the burner. LES is based on a transported probability density function model within the framework of Eulerian Stochastic Fields (PDF-ESF). It is found that local extinction occurs when the scalar dissipation rate around the stoichiometric mixture fraction is high. The characteristic time scale for local extinction and re-ignition in the present flames is an order of magnitude longer than the characteristic time scale of diffusion/extinction of laminar flamelets. There are two mechanisms for flame hole re-ignition in the present flames. First, under low degree of local extinction conditions (i.e., for small flame holes surrounded by flames) the flame hole re-ignition is due to the mechanism of turbulent flame folding. Second, under high degree of extinction conditions (i.e., with large regions of extinction and lifted flames), re-ignition of the locally extinguished flame is due to the mechanism of ignition assisted partially premixed flame propagation. The results show that the PDF-ESF model is capable of simulating the quenching and re-ignition process found in the experiments.</p>},
  author       = {Yu, S. and Liu, X. and Bai, X. S. and Elbaz, A. M. and Roberts, W. L.},
  issn         = {0010-2180},
  language     = {eng},
  pages        = {102--119},
  publisher    = {Elsevier},
  series       = {Combustion and Flame},
  title        = {LES/PDF modeling of swirl-stabilized non-premixed methane/air flames with local extinction and re-ignition},
  url          = {http://dx.doi.org/10.1016/j.combustflame.2020.05.018},
  doi          = {10.1016/j.combustflame.2020.05.018},
  volume       = {219},
  year         = {2020},
}