Formation and stabilization of multiple ball-like flames at Earth gravity
| Autor: | Jeroen A. van Oijen, Yuriy Shoshin, Laurentius P.H. de Goey, Francisco E. Hernández-Pérez, Zhen Zhou |
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| Přispěvatelé: | Power & Flow, Mechanical Engineering, Group De Goey, Group Van Oijen |
| Rok vydání: | 2018 |
| Předmět: |
Premixed flame
Low Lewis number Materials science 010304 chemical physics General Chemical Engineering General Physics and Astronomy Energy Engineering and Power Technology General Chemistry Mechanics Lean flammability limit Combustion Ball-like flame 01 natural sciences Flow field Lewis number 010305 fluids & plasmas Physics::Fluid Dynamics Fuel Technology Planar Gravity of Earth 0103 physical sciences Ball (bearing) Physics::Chemical Physics Hydrogen–methane Equivalence ratio |
| Zdroj: | Combustion and Flame, 192, 35-43. Elsevier |
| ISSN: | 0010-2180 |
| DOI: | 10.1016/j.combustflame.2018.01.034 |
| Popis: | Near-limit low-Lewis-number premixed flame behavior is studied experimentally and numerically for flames of H2–CH4–air mixtures that are located in a 55 mm diameter tube and below a perforated plate in a downward mixture flow. A combustion regime diagram is experimentally identified in terms of equivalence ratio and ratio of H2 to CH4 (variation of fuel Lewis number). Planar flames, cell-like flames, distorted cap-like flames, and arrays of ball-like flames are progressively observed in the experiments as the equivalence ratio is decreased. The experimentally observed ball-like lean limit flames experience chaotic motion, which is accompanied by sporadic events of flame splitting and extinction, while the total number of simultaneously burning flamelets remains approximately the same. In separate experiments, the multiple ball-like lean limit flames are stabilized by creating a slightly non-uniform mixture flow field. The CH* chemiluminescence distributions of the lean limit flames are recorded, showing that the ball-like lean limit flame front becomes more uniform in intensity and its shape approaches a spherical one with the increase of H2 content in the fuel. Numerical simulations are performed for single representative flames of the array of stabilized flamelets observed in the experiments. The simulated ball-like lean limit flame is further contrasted with the single ball-like flame that forms in a narrow tube (13.5 mm inner diameter) with an iso-thermal wall. The numerical results show that the ball-like lean limit flames present in the array of ball-like flames are more affected by the buoyancy-induced recirculation zone, compared with that in the narrow tube, revealing why the shape of the ball-like flame in the array deviates more from a spherical one. All in all, the wall confinement is not crucial for the formation of ball-like flames at terrestrial gravity. |
| Databáze: | OpenAIRE |
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