Effects of the Lewis number and radiative heat loss on the bifurcation and extinction of CH₄/O₂-N₂-He flames

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TypeArticle
Journal titleJournal of Fluid Mechanics
ISSN0022-1120
Volume379
Issue1
Pages165190; # of pages: 26
AbstractEffects of the Lewis number and radiative heat loss on flame bifurcations and extinction of CH₄ /O₂-N₂-He flames are investigated numerically with detailed chemistry. Attention is paid to the interaction between radiation heat loss and the Lewis number effect. The Planck mean absorption coeffcients of CO, CO₂, and H₂O are calculated using the statistical narrow-band model and compared with the data given by Tien. The use of Tien's Planck mean absorption coeffcients overpredicts radiative heat loss by nearly 30% in a counterflow configuration. The new Planck mean absorption coeffcients are then used to calculate the extinction limits of the planar propagating flame and the counterflow flame when the Lewis number changes from 0.967 to 1.8. The interaction between radiation heat loss and the Lewis number effect greatly enriches the phenomenon of flame bifurcation. The existence of multiple flames is shown to be a physically intrinsic phenomenon of radiating counterflow flames. Eight kinds of typical patterns of flame bifurcation are identified. The competition between radiation heat loss and the Lewis number effect results in two distinct phenomena, depending on if the Lewis number is greater or less than a critical value. Comparisons between the standard limits of the unstrained flames and the flammability limits of the counterflow flames indicate that the flammability limit of the counterflow flame is lower than the standard limit when the Lewis number is less than the critical value and is equal to the standard limit when the Lewis number is higher than this critical value. Finally, a G-shaped curve and a K-shaped curve which respectively represent the flammable regions of the multiple flames for Lewis numbers lower and higher than the critical value are obtained. The G- and K-shaped curves show a clear relationship between the stretched counterflow flame and the unstrained planar flame. The present results provide a good explanation of the physics revealed experimentally in microgravity.
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Copyright noticeCambridge University Press prefers to provide access to full text through the publisher's site. The Publisher's version/PDF may be used
Linkhttp://adsabs.harvard.edu/abs/1999JFM...379..165J
LanguageEnglish
AffiliationNRC Institute for Chemical Process and Environmental Technology; National Research Council Canada
Access conditionavailable
unlimited
public
Peer reviewedYes
Identifier10012813
NRC number50912
NPARC number2994869
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Record identifier040d3a8d-4b35-426d-94e7-2405413c95ed
Record created2009-08-07
Record modified2017-03-23
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