Abstract
We have recently shown that premixed CH4/air flames anchored behind flame holders can stabilize in two flame stabilization regimes characterised by the presence or absence of a recirculation vortex [1]. Focus of the present work is on the underlying mechanisms governing flames anchored without the presence of a vortex for methane-air flames. We revisit the definition of the flame anchoring location and define a new anchoring location which results from flame stretch considerations rather than heat loss considerations. This location can be unambiguously defined for flame holders of different sizes. It is argued that such an anchoring location is more relevant for flames stabilized behind flame holders with sharp corners and do take into account the multi-dimensional nature of heat transfer with the flame holder as well. A quantitative assessment of heat transfer, stretch and preferential diffusion effects is then carried out at the anchoring location for elucidating their impact on the flame speed as a function of the flame holder size. New insights into flame blow-off, flashback and emergence of a recirculation vortex are obtained as a result of this investigation.
Highlights
The manner in which a premixed CH4/air flame stabilizes is crucial for our understanding and the design of burners for different fuels
We have recently shown that premixed CH4/air flames anchored behind flame holders can stabilize in two flame stabilization regimes characterised by the presence or absence of a recirculation vortex [1]
Our objective is to investigate in detail the flame anchoring mechanisms in the absence of a recirculation zone (RZ) for the cases presented in Ref. [1] in the case of CH4-air flames and this will contribute to the formation of a generalized overview of the flame anchoring process
Summary
The manner in which a premixed CH4/air flame stabilizes is crucial for our understanding and the design of burners for different fuels. We discussed trends of heat loss to the flame holder, flame curvature and flow strain for each of the stabilization regimes. [1] in the case of CH4-air flames and this will contribute to the formation of a generalized overview of the flame anchoring process. This motivation follows the pioneering works by Lewis and von Elbe [14] on the stabilization of premixed flames on flame holders of various sizes. Critical velocity gradient theory of Lewis and von Elbe, did not take into account the effects of flow strain, flame curvature, conjugate heat transfer with the flame holder and preferential diffusion effects. Researchers are focusing on numerical simulations for extracting detailed information and understanding the flame anchoring process
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