open access

https://hdl.handle.net/2115/71130

Onset mechanism of primary acoustic instability in downward-propagating flames

英語

Reduced wave number

2016-08

Elsevier

Combustion and flame

170

1-11

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.

学術雑誌論文

Accepted Manuscript

Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International

© 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/

0010-2180