Diffusion flames and diffusion flame-streets in three dimensional micro-channels

S. Mohan, Moshe Matalon

Research output: Contribution to journalArticle

Abstract

Experiments of non-premixed combustion in micro-channels have exhibited different modes of burning. Typically, a diffusion flame is established along or near the axis of a channel spanning the entire mixing layer. It separates a region of fuel and no oxidiser from a region with only oxidiser. Often, however, a periodic sequence of extinction and reignition events, termed collectively as “diffusion flame-streets”, are observed. They constitute a series of separate diffusion flames, each with a tribrachial edge flame structure that is stabilised along the channel. The current work focuses on understanding the underlying mechanism responsible for these unique observations. Numerical simulations were conducted in a thermo-diffusive limit to examine the effects of confinement and heat loss on flames in three dimensional micro-channels with low aspect ratios. An asymptotic analysis was used to reduce the mathematical equations into a two-dimensional problem which effectively captured the three dimensional nature of the combustion process. Two key burning regimes were identified: (i) stable continuous diffusion flames and (ii) stable diffusion flame-streets. The transition between regimes is demarcated primarily by the Damköhler number, defined as the ratio of a diffusion time to a chemical reaction time, but is also influenced by the extent of heat loss. Occasionally within the diffusion flame-street regime, the residual mixture would reignite but would fail to evolve into stationary auxiliary flames. This was generally observed at low flow-rates for Reynolds numbers below a critical value. The behaviour appeared to be periodic in time with a frequency that depended on the removal from criticality.

Original languageEnglish (US)
Pages (from-to)155-170
Number of pages16
JournalCombustion and Flame
Volume177
DOIs
StatePublished - Jan 1 2017

Fingerprint

streets
diffusion flames
flames
Heat losses
low aspect ratio
heat
Asymptotic analysis
reaction time
ignition
Reynolds number
chemical reactions
extinction
flow velocity
Aspect ratio
Chemical reactions
Flow rate
Computer simulation
simulation

Keywords

  • Diffusion flame
  • Diffusion flame-street
  • Edge flame
  • Extinction–reignition
  • Heat loss
  • Micro-combustion

ASJC Scopus subject areas

  • Chemistry(all)
  • Chemical Engineering(all)
  • Fuel Technology
  • Energy Engineering and Power Technology
  • Physics and Astronomy(all)

Cite this

Diffusion flames and diffusion flame-streets in three dimensional micro-channels. / Mohan, S.; Matalon, Moshe.

In: Combustion and Flame, Vol. 177, 01.01.2017, p. 155-170.

Research output: Contribution to journalArticle

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