Numerical computations and optical diagnostics of unsteady partially premixed methane/air flames

Journal Article · Sat May 15 00:00:00 EDT 2010 · Combustion and Flame

DOI:https://doi.org/10.1016/J.COMBUSTFLAME.2009.11.012· OSTI ID:21305710

Nogenmyr, K J; Bai, X S ^[1]; Kiefer, J ^[2]; Li, Z S; Alden, M ^[3]

---

1. Division of Fluid Mechanics, Lund University, P.O. Box 118, S-221 00 Lund (Sweden)
2. Lehrstuhl fuer Technische Thermodynamik and Erlangen Graduate School in Advanced Optical Technologies, Universitaet Erlangen-Nuernberg, Am Weichselgarten 8, D-91058 Erlangen (Germany)
3. Division of Combustion Physics, Lund University, P.O. Box 118, S-221 00 Lund (Sweden)

The structures and dynamics of unsteady laminar partially premixed methane/air Bunsen flames are studied by means of numerical simulations, OH and CH PLIF imaging, and high speed chemiluminescence imaging employing a high framing speed intensified charge coupled device camera. The Bunsen burner has a diameter of 22 mm. Rich methane/air mixtures with an equivalence ratio of 1.5 are injected from the burner into atmosphere at different flow speeds ranging from 0.77 to 1.7 m/s, with Reynolds numbers based on the nozzle flow ranging from 1100 to 2500. The numerical simulations are based on a two-scalar flamelet manifold tabulation approach. Detailed chemistry is used to generate the flamelet manifold tabulation which relates the species concentrations, reaction rates, temperature and density to a distance function G and mixture fraction Z. Two distinct reaction zones are identified using CH and OH PLIF imaging and numerical simulations; one inner reaction zone corresponds to premixed flames on the rich side of the mixture and one outer reaction zone corresponds to mixing controlled diffusion flames on the lean side of the mixture. Under normal gravity conditions both the inner premixed flames and the outer diffusion flames are unsteady. The outer diffusion flames oscillate with a flickering frequency of about 15 Hz, which slightly increases with the burner exit velocity. The inner premixed flames are more random with much more small-scale wrinkling structures. Under zero gravity conditions the outer diffusion flames are stable whereas the inner premixed flames are unstable and highly wrinkled. It appears that the outer diffusion flames are governed by the Rayleigh-Taylor instability whereas the inner premixed flames are dictated by Landau-Darrieus instability. The two-scalar flamelet approach is shown to capture the basic structures and dynamics of the investigated unsteady partially premixed flames. (author)

• OSTI ID: 21305710
• Journal Information: Combustion and Flame, Vol. 157, Issue 5; Other Information: Elsevier Ltd. All rights reserved; ISSN 0010-2180
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
METHANE
AIR
LAMINAR FLAMES
MIXTURES
COMPUTERIZED SIMULATION
RAYLEIGH-TAYLOR INSTABILITY
DIFFUSION
BURNERS
OSCILLATIONS
HZ RANGE
ZONES
CALCULATION METHODS
COMBUSTION KINETICS
REYNOLDS NUMBER
DENSITY
SCALARS
VELOCITY
DISTANCE
FUNCTIONS
GRAVITATION
MIXING
RANDOMNESS
WEIGHTLESSNESS
Partially premixed flames
Double-flame structure
Buoyancy
Planar laser-induced fluorescence