TY - JOUR
T1 - Experimental observation of pulsating instability under acoustic field in downward-propagating flames at large Lewis number
AU - Yoon, Sung Hwan
AU - Hu, Longhua
AU - Fujita, Osamu
N1 - KAUST Repository Item: Exported on 2020-10-01
Acknowledgements: The author would like to acknowledge the support from these projects: A Grant-in-Aid for Scientific Research (KIBAN (B) No. 26289042) from MEXT Japan, Key project of National Natural Science Foundation of China (NSFC) under Grant No. 51636008 and Key Research Program of Frontier Sciences, Chinese Academy of Science (CAS) under Grant No. QYZDB-SSW-JSC029. The authors thank Dr. M. S. Cha for his valuable assistance.
PY - 2017/10/12
Y1 - 2017/10/12
N2 - According to previous theory, pulsating propagation in a premixed flame only appears when the reduced Lewis number, β(Le-1), is larger than a critical value (Sivashinsky criterion: 4(1 +3) ≈ 11), where β represents the Zel'dovich number (for general premixed flames, β ≈ 10), which requires Lewis number Le > 2.1. However, few experimental observation have been reported because the critical reduced Lewis number for the onset of pulsating instability is beyond what can be reached in experiments. Furthermore, the coupling with the unavoidable hydrodynamic instability limits the observation of pure pulsating instabilities in flames. Here, we describe a novel method to observe the pulsating instability. We utilize a thermoacoustic field caused by interaction between heat release and acoustic pressure fluctuations of the downward-propagating premixed flames in a tube to enhance conductive heat loss at the tube wall and radiative heat loss at the open end of the tube due to extended flame residence time by diminished flame surface area, i.e., flat flame. The thermoacoustic field allowed pure observation of the pulsating motion since the primary acoustic force suppressed the intrinsic hydrodynamic instability resulting from thermal expansion. By employing this method, we have provided new experimental observations of the pulsating instability for premixed flames. The Lewis number (i.e., Le ≈ 1.86) was less than the critical value suggested previously.
AB - According to previous theory, pulsating propagation in a premixed flame only appears when the reduced Lewis number, β(Le-1), is larger than a critical value (Sivashinsky criterion: 4(1 +3) ≈ 11), where β represents the Zel'dovich number (for general premixed flames, β ≈ 10), which requires Lewis number Le > 2.1. However, few experimental observation have been reported because the critical reduced Lewis number for the onset of pulsating instability is beyond what can be reached in experiments. Furthermore, the coupling with the unavoidable hydrodynamic instability limits the observation of pure pulsating instabilities in flames. Here, we describe a novel method to observe the pulsating instability. We utilize a thermoacoustic field caused by interaction between heat release and acoustic pressure fluctuations of the downward-propagating premixed flames in a tube to enhance conductive heat loss at the tube wall and radiative heat loss at the open end of the tube due to extended flame residence time by diminished flame surface area, i.e., flat flame. The thermoacoustic field allowed pure observation of the pulsating motion since the primary acoustic force suppressed the intrinsic hydrodynamic instability resulting from thermal expansion. By employing this method, we have provided new experimental observations of the pulsating instability for premixed flames. The Lewis number (i.e., Le ≈ 1.86) was less than the critical value suggested previously.
UR - http://hdl.handle.net/10754/626037
UR - http://www.sciencedirect.com/science/article/pii/S0010218017303632
UR - http://www.scopus.com/inward/record.url?scp=85030714107&partnerID=8YFLogxK
U2 - 10.1016/j.combustflame.2017.09.026
DO - 10.1016/j.combustflame.2017.09.026
M3 - Article
SN - 0010-2180
VL - 188
SP - 1
EP - 4
JO - Combustion and Flame
JF - Combustion and Flame
ER -