Impact of fuel composition on the recirculation zone structure and its role in lean premixed flame anchoring

Handle URI:
http://hdl.handle.net/10754/598564
Title:
Impact of fuel composition on the recirculation zone structure and its role in lean premixed flame anchoring
Authors:
Hong, Seunghyuck; Shanbhogue, Santosh J.; Ghoniem, Ahmed F.
Abstract:
© 2014 The Combustion Institute. Published by Elsevier Inc. All rights reserved. We investigate the dependence of the recirculation zone (RZ) size and structure on the fuel composition using high-speed particle image velocimetry (PIV) and chemiluminescence measurements for C3H8/H2/air lean premixed flames stabilized in a backward-facing step combustor. Results show an intricate coupling between the flame anchoring and the RZ structure and length. For a fixed fuel composition, at relatively low equivalence ratios, the time-averaged RZ is comprised of two counter rotating eddies: a primary eddy (PE) between the shear layer and the bottom wall; and a secondary eddy (SE) between the vertical step wall and the PE. The flame stabilizes downstream of the saddle point of the dividing streamline between the two eddies. As equivalence ratio is raised, the flame moves upstream, pushing the saddle point with it and reducing the size of the SE. Higher temperature of the products reduces the velocity gradient in the shear layer and thus the reattachment length. As equivalence ratio approaches a critical value, the saddle point reaches the step and the SE collapses while the flame starts to exhibit periodic flapping motions, suggesting a correlation between the RZ structure and flame anchoring. The overall trend in the flow field is the same as we add hydrogen to the fuel at a fixed equivalence ratio, demonstrating the impact of fuel composition on the flow field. We show that the reattachment lengths (LR), which are shown to encapsulate the mean RZ structure, measured over a range of fuel composition and equivalence ratio collapse if plotted against the strained consumption speed (Sc). Results indicate that for the flame to remain anchored, the RZ structure should satisfy lR,isothermal/L R,reacting · S c/U ∞ ∼ 0.1. If this criterion cannot be met, the flame blows off, flashes back or becomes thermoacoustically unstable, suggesting a Damköhler-like criterion for aerodynamic flame stabilization in backward-facing step flows.
Citation:
Hong S, Shanbhogue SJ, Ghoniem AF (2015) Impact of fuel composition on the recirculation zone structure and its role in lean premixed flame anchoring. Proceedings of the Combustion Institute 35: 1493–1500. Available: http://dx.doi.org/10.1016/j.proci.2014.05.150.
Publisher:
Elsevier BV
Journal:
Proceedings of the Combustion Institute
KAUST Grant Number:
KUS-110-010-01
Conference/Event name:
30th International Symposium on Combustion
Issue Date:
2015
DOI:
10.1016/j.proci.2014.05.150
Type:
Conference Paper
ISSN:
1540-7489
Sponsors:
This work was funded by the KAUST Grant No. KUS-110-010-01.
Appears in Collections:
Publications Acknowledging KAUST Support

Full metadata record

DC FieldValue Language
dc.contributor.authorHong, Seunghyucken
dc.contributor.authorShanbhogue, Santosh J.en
dc.contributor.authorGhoniem, Ahmed F.en
dc.date.accessioned2016-02-25T13:32:14Zen
dc.date.available2016-02-25T13:32:14Zen
dc.date.issued2015en
dc.identifier.citationHong S, Shanbhogue SJ, Ghoniem AF (2015) Impact of fuel composition on the recirculation zone structure and its role in lean premixed flame anchoring. Proceedings of the Combustion Institute 35: 1493–1500. Available: http://dx.doi.org/10.1016/j.proci.2014.05.150.en
dc.identifier.issn1540-7489en
dc.identifier.doi10.1016/j.proci.2014.05.150en
dc.identifier.urihttp://hdl.handle.net/10754/598564en
dc.description.abstract© 2014 The Combustion Institute. Published by Elsevier Inc. All rights reserved. We investigate the dependence of the recirculation zone (RZ) size and structure on the fuel composition using high-speed particle image velocimetry (PIV) and chemiluminescence measurements for C3H8/H2/air lean premixed flames stabilized in a backward-facing step combustor. Results show an intricate coupling between the flame anchoring and the RZ structure and length. For a fixed fuel composition, at relatively low equivalence ratios, the time-averaged RZ is comprised of two counter rotating eddies: a primary eddy (PE) between the shear layer and the bottom wall; and a secondary eddy (SE) between the vertical step wall and the PE. The flame stabilizes downstream of the saddle point of the dividing streamline between the two eddies. As equivalence ratio is raised, the flame moves upstream, pushing the saddle point with it and reducing the size of the SE. Higher temperature of the products reduces the velocity gradient in the shear layer and thus the reattachment length. As equivalence ratio approaches a critical value, the saddle point reaches the step and the SE collapses while the flame starts to exhibit periodic flapping motions, suggesting a correlation between the RZ structure and flame anchoring. The overall trend in the flow field is the same as we add hydrogen to the fuel at a fixed equivalence ratio, demonstrating the impact of fuel composition on the flow field. We show that the reattachment lengths (LR), which are shown to encapsulate the mean RZ structure, measured over a range of fuel composition and equivalence ratio collapse if plotted against the strained consumption speed (Sc). Results indicate that for the flame to remain anchored, the RZ structure should satisfy lR,isothermal/L R,reacting · S c/U ∞ ∼ 0.1. If this criterion cannot be met, the flame blows off, flashes back or becomes thermoacoustically unstable, suggesting a Damköhler-like criterion for aerodynamic flame stabilization in backward-facing step flows.en
dc.description.sponsorshipThis work was funded by the KAUST Grant No. KUS-110-010-01.en
dc.publisherElsevier BVen
dc.subjectBackward-facing stepen
dc.subjectFlame anchoringen
dc.subjectParticle image velocimetry (PIV)en
dc.subjectRecirculation zone lengthen
dc.subjectStrained consumption speeden
dc.titleImpact of fuel composition on the recirculation zone structure and its role in lean premixed flame anchoringen
dc.typeConference Paperen
dc.identifier.journalProceedings of the Combustion Instituteen
dc.conference.date2004-07-25 to 2004-07-30en
dc.conference.name30th International Symposium on Combustionen
dc.conference.locationChicago, IL, USAen
dc.contributor.institutionMassachusetts Institute of Technology, Cambridge, United Statesen
kaust.grant.numberKUS-110-010-01en
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