Impact of fuel composition on the recirculation zone structure and its role in lean premixed flame anchoring
Name
HongShanbhogueGhoniem_PCI2015_finalManuscript_accepted.pdf
Size
5.73 MB
Format
Adobe PDF
Checksum (MD5)
d57cbfe72e6849a9cd62329bac3e356d
Author(s)
Ghoniem, Ahmed F.
Hong, Seung hyuck
Shanbhogue, Santosh
Date Issued
June 2014
Journal
Proceedings of the Combustion Institute
Publisher
Elsevier
Citation
Hong, Seunghyuck, Santosh J. Shanbhogue, and Ahmed F. Ghoniem. “Impact of Fuel Composition on the Recirculation Zone Structure and Its Role in Lean Premixed Flame Anchoring.” Proceedings of the Combustion Institute 35, no. 2 (2015): 1493–1500.
Version
Author's final manuscript
Abstract
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 C[subscript 3]H[subscript 8]/H[subscript 2]/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 (L[subscript R]), 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 (S[subscript c]). Results indicate that for the flame to remain anchored, the RZ structure should satisfy [L[subscript R,isothermal] over L[subscript R,reacting]] · [S[subscript c] over U[subscript ∞]] ~ 0.1. If this criterion cannot be met, the flame blows off, flashes back or becomes thermoacoustically unstable, suggesting a Damkohler-like criterion for aerodynamic flame stabilization in backward-facing step flows.
MIT Department
Massachusetts Institute of Technology. Department of Mechanical Engineering
Terms of Use
Creative Commons Attribution
Persistent DSpace Link
DOI of Published Version
https://doi.org/10.1016/j.proci.2014.05.150
