Characteristics of counterflow premixed flames with low frequency composition fluctuations

Takuya Tomidokoro, Takeshi Yokomori, Hong G. Im, Toshihisa Ueda

Research output: Contribution to journalArticle

Abstract

The response of laminar methane/air counterflow premixed flames under sinusoidal equivalence ratio oscillation was investigated numerically. The timescales of the oscillation were chosen to be sufficiently longer than the flame timescale so that the flame responds quasi-steadily. The response of periodically stratified flame (SF) with a detailed reaction mechanism exhibited the “back-support” effect, in that the consumption speed Sc response deviated increasingly from Sc of steady homogeneous flames (HFs) at higher oscillation frequencies. It was shown that even when the imposed oscillation timescale is much longer than the flame timescale, the flame response can still be delayed under a sufficiently large equivalence ratio gradient. Subsequently, the above results were compared with those obtained with a global four-step mechanism that omits back-diffusion radicals into the reaction zone. As a result, SFs with the global mechanism displayed a much smaller back-support effect in both lean and rich mixtures. Further analysis with modified diffusion coefficients revealed the dominant roles of H2 and radical species diffusion in inducing the back-support effect. Contrary to the previous findings, variations in burned gas temperature were found to play a negligible role in modifying Sc. Additionally, the hysteresis of the back-support effect under periodical stratification was found to be more prominent on the richer side because of the presence of a larger H2 pool.

Original languageEnglish
Pages (from-to)13-24
Number of pages12
JournalCombustion and Flame
Volume212
DOIs
Publication statusPublished - 2020 Feb

Fingerprint

counterflow
premixed flames
flames
low frequencies
Chemical analysis
oscillations
Methane
equivalence
Hysteresis
Gases
species diffusion
gas temperature
Air
stratification
methane
diffusion coefficient
hysteresis
gradients
Temperature
air

Keywords

  • Back-support effect
  • Consumption speed
  • Quasi-steady response
  • Stratified combustion
  • Unsteady flames

ASJC Scopus subject areas

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

Cite this

Characteristics of counterflow premixed flames with low frequency composition fluctuations. / Tomidokoro, Takuya; Yokomori, Takeshi; Im, Hong G.; Ueda, Toshihisa.

In: Combustion and Flame, Vol. 212, 02.2020, p. 13-24.

Research output: Contribution to journalArticle

Tomidokoro, Takuya ; Yokomori, Takeshi ; Im, Hong G. ; Ueda, Toshihisa. / Characteristics of counterflow premixed flames with low frequency composition fluctuations. In: Combustion and Flame. 2020 ; Vol. 212. pp. 13-24.
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