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Impact of the Lewis number on finger flame acceleration at the early stage of burning in channels and tubes
Department of Mechanical and Aerospace Engineering, West Virginia University, Morgantown, West Virginia 26506, USA.
Department of Mechanical and Aerospace Engineering, West Virginia University, Morgantown, West Virginia 26506, USA.
Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics. Center for Combustion Energy, Key Laboratory for Thermal Science and Power Engineering of Ministry of Education of China, Department of Energy and Power Engineering, Tsinghua University, Beijing, China.
Department of Mechanical and Aerospace Engineering, West Virginia University, Morgantown, West Virginia 26506, USA.
2019 (English)In: Physics of fluids, ISSN 1070-6631, E-ISSN 1089-7666, Vol. 31, no 8, article id 083606Article in journal (Refereed) Published
Abstract [en]

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 ≠ 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 ≠ 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.

Place, publisher, year, edition, pages
American Institute of Physics (AIP), 2019. Vol. 31, no 8, article id 083606
National Category
Other Mechanical Engineering
Identifiers
URN: urn:nbn:se:umu:diva-162173DOI: 10.1063/1.5108805OAI: oai:DiVA.org:umu-162173DiVA, id: diva2:1343133
Available from: 2019-08-15 Created: 2019-08-15 Last updated: 2019-08-16Bibliographically approved

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Valiev, Damir

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