Effect of geometrical parameters on thermo-acoustic instability of downward propagating flames in tubes

Ajit Kumar Dubey, Yoichiro Koyama, Nozomu Hashimoto, Osamu Fujita

Research output: Contribution to journalArticlepeer-review

6 Citations (Scopus)

Abstract

Experiments and theoretical analysis are presented to clarify the effect of geometrical parameters on thermo-acoustic instability of downward propagating flames in tubes. The experiments reveal that the longer tubes have higher instability compared to shorter tubes and the lower diameter tubes have higher instability compared to higher diameter tubes. The secondary instability leading to turbulent burning is found to be more sensitive to change in geometrical parameters compared to primary instability (oscillating flat flame). The secondary instability is re-stabilized for some intermediate burning velocity conditions even though lower and higher burning velocity conditions show secondary instability. The appearance of such re-stabilization is only observed for some specific lengths of the tube. Present experimental observations pertaining to the effect of geometrical parameters is found to be contradicting the theoretical predictions based on pressure coupling mechanism. To clear the underlying mechanism, analytical growth rate is computed considering velocity coupling mechanism. The computed growth rates correctly predict the effect of geometrical parameters on thermo-acoustic instability of downward propagating flames. This work provides further evidence to believe that the flame -acoustic coupling in downward propagating flames is due to flame area modulation (leading to heat release modulation) through action of acoustic acceleration.

Original languageEnglish
Pages (from-to)1869-1877
Number of pages9
JournalProceedings of the Combustion Institute
Volume37
Issue number2
DOIs
Publication statusPublished - 2019
Externally publishedYes

Keywords

  • Combustion tube
  • Downward propagating flames
  • Effect of geometrical parameters
  • Thermo-acoustic instability

ASJC Scopus subject areas

  • Chemical Engineering(all)
  • Mechanical Engineering
  • Physical and Theoretical Chemistry

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