Journal
PROGRESS IN ENERGY AND COMBUSTION SCIENCE
Volume 42, Issue -, Pages 1-34Publisher
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.pecs.2014.01.003
Keywords
Tubular flames; Raman scattering; Stretched flames; Curvature Cellular flames; Flame instabilities; Premixed flames; Diffusion flames
Funding
- National Science Foundation [CBET-1134268, CTS-0314704]
- NASA Microgravity Program [NNC04AA14A]
- National Science Foundation of China [51106131]
- Fundamental Research Funds for the Central Universities of China [2010121045]
- Scientific Research Foundation for the Returned Overseas Chinese Scholars, State Education Ministry
- Div Of Chem, Bioeng, Env, & Transp Sys
- Directorate For Engineering [1134268] Funding Source: National Science Foundation
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Tubular flames are ideal for the study of stretch and curvature effects on flame structure, extinction, and instabilities. Tubular flames have uniform stretch and curvature and each parameter can be varied independently. Curvature strengthens or weakens preferential diffusion effects on the tubular flame and the strengthening or weakening is proportional to the ratio of the flame thickness to the flame radius. Premixed flames can be studied in the standard tubular burner where a single premixed gas stream flows radially inward to the cylindrical flame surface and products exit as opposed jets. Premixed, diffusion and partially premixed flames can be studied in the opposed tubular flame where opposed radial flows meet at a cylindrical stagnation surface and products exit as opposed jets. The tubular flame flow configurations can be mathematically reduced to a two-point boundary value solution along the single radial coordinate. Non-intrusive measurements of temperature and major species concentrations have been made with laser-induced Raman scattering in an optically accessible tubular burner for both premixed and diffusion flames. The laser measurements of the flame structure are in good agreement with numerical simulations of the tubular flame. Due to the strong enhancement of preferential diffusion effects in tubular flames, the theory-data comparison can be very sensitive to the molecular transport model and the chemical kinetic mechanism. The strengthening or weakening of the tubular flame with curvature can increase or decrease the extinction strain rate of tubular flames. For lean H-2-air mixtures, the tubular flame can have an extinction strain rate many times higher than the corresponding opposed jet flame. More complex cellular tubular flames with highly curved flame cells surrounded by local extinction can be formed under both premixed and non-premixed conditions. In the hydrogen fueled premixed tubular flames, thermal-diffusive flame instabilities result in the formation of a uniform symmetric petal flames far from extinction. In opposed-flow tubular diffusion flames, thermal-diffusive flame instabilities result in cellular flames very close to extinction. Both of these flames are candidates for further study of flame curvature and extinction. (C) 2014 Elsevier Ltd. All rights reserved.
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