Journal
PHYSICS OF FLUIDS
Volume 31, Issue 8, Pages -Publisher
AMER INST PHYSICS
DOI: 10.1063/1.5108805
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Funding
- U.S. National Science Foundation (NSF), through CAREER Award [1554254]
- West Virginia Higher Education Policy Commission (HEPC) [HEPC.dsr.18.7]
- National Natural Science Foundation of China (NSFC) [51750110503]
- Thousand Young Talents Plan program
- Div Of Chem, Bioeng, Env, & Transp Sys
- Directorate For Engineering [1554254] Funding Source: National Science Foundation
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For premixed combustion in channels and tubes with one end open, when a flame is ignited at the centerline at the closed end of the pipe and it propagates toward the open one, significant flame acceleration occurs at an early stage of the combustion process due to formation of a finger-shaped flame front. This scenario is tagged finger flame acceleration (FFA), involving an initially hemispherical flame kernel, which subsequently acquires a finger shape with increasing surface area of the flame front. Previous analytical and computational studies of FFA employed a conventional assumption of equidiffusivity when the thermal-to-mass-diffusivity ratio (the Lewis number) is unity (Le = 1). However, combustion is oftentimes nonequidiffusive (Le not equal 1) in practice such that there has been a need to identify the role of Le in FFA. This demand is addressed in the present work. Specifically, the dynamics and morphology of the Le not equal 1 flames in two-dimensional (2D) channels and cylindrical tubes are scrutinized by means of the computational simulations of the fully compressible reacting flow equations, and the role of Le is identified. Specifically, the Le > 1 flames accelerate slower as compared with the equidiffusive ones. In contrast, the Le < 1 flames acquire stronger distortion of the front, experience the diffusional-thermal combustion instability, and thereby accelerate much faster than the Le = 1 flames. In addition, combustion in a cylindrical configuration shows stronger FFA than that under the same burning conditions in a 2D planar geometry. Published under license by AIP Publishing.
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