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Onset mechanism of primary acoustic instability in downward-propagating flames

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Title: Onset mechanism of primary acoustic instability in downward-propagating flames
Authors: Yoon, Sung Hwan Browse this author
Noh, Tae Joon Browse this author
Fujita, Osamu Browse this author →KAKEN DB
Keywords: Acoustic instability
Coupling mechanism
Growth rate
Lewis number
Reduced wave number
Issue Date: Aug-2016
Publisher: Elsevier
Journal Title: Combustion and flame
Volume: 170
Start Page: 1
End Page: 11
Publisher DOI: 10.1016/j.combustflame.2016.05.008
Abstract: This paper deals with the onset mechanism of primary acoustic instability of downward-propagating flames in a combustion tube. We focus on the effects of a coupling constant, βM, where β and M represent the Zel'dovich and Mach numbers, respectively, and the variation in the flame surface area. To change the coupling constant, various gas compositions for lean ethylene flames diluted with carbon dioxide or nitrogen are used. We obtain a linear relationship between the coupling constant and the average acoustic intensity, and the critical values of the coupling constants are acquired through linear approximation regarding the onset of the primary acoustic instability. Furthermore, we adopt the CO2 laser irradiation method to alter the shape of the flame front, and experimental results show that the variation in the flame surface area does not always cause spontaneous generation of the primary acoustic instability in initially nonvibrating flames. Furthermore, even in initially vibrating flames, the growth rate of the primary acoustic instability is not associated with the growth or decline in the flame surface area in the present experiments. Finally, we also estimate the effects of acoustic losses on acoustic instability. Larger total acoustic losses tend to suppress acoustic vibration even at the same coupling constant. In addition, a remarkable transition from a secondary acoustic instability to the primary acoustic instability is observed at strong laser irradiation and is briefly discussed.
Rights: © 2016. This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/
http://creativecommons.org/licenses/by-nc-nd/4.0/
Type: article (author version)
URI: http://hdl.handle.net/2115/71130
Appears in Collections:工学院・工学研究院 (Graduate School of Engineering / Faculty of Engineering) > 雑誌発表論文等 (Peer-reviewed Journal Articles, etc)

Submitter: 藤田 修

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