A numerical investigation of the flame structure of an unsteady inverse partially premixed flame

Journal Article · Mon Dec 01 04:00:00 EST 1997 · Combustion and Flame

DOI:https://doi.org/10.1016/S0010-2180(97)00007-2· OSTI ID:543509

Shu, Z; Aggarwal, S K; Puri, I K ^[1]; Katta, V R ^[2]

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1. Univ. of Illinois, Chicago, IL (United States). Dept. of Mechanical Engineering
2. Innovative Scientific Solutions, Inc., Dayton, OH (United States)

The flame structure of unsteady flickering partially premixed flames is numerically investigated, and detailed results are provided for a flame established at Fr = 0.5, Re = 500, and overall {phi} = 1. A numerical study is conducted in an inverse configuration in which a fuel-rich (CH{sub 4}-air) annular jet is sandwiched between an axisymmetric air jet (on the inside) and coflowing air (on the outside). The computations involve a time-dependent, axisymmetric model based on a direct numerical simulation methodology, and a detailed 52-step mechanism to model the CH{sub 4}-air chemistry. The calculations show that the flame structure of the partially premixed flames differs from that of a typical nonpremixed laminar jet flame. The fuel-rich annular ring close to the nozzle exit undergoes premixed combustion, but once oxygen is depleted inside the annular ring, diffusion flames are established on both sides of it due to excess fuel emerging from the premixed zone. The effect of unsteadiness on flame structure is investigated by comparing the scalar profiles at different times with respect to a conserved scalar. The predictions do not reveal significant effects of unsteadiness on the flame structure, although buoyant convection may influence the heat transfer to the unreacted flow. This is because the rollup process essentially affects the postflame, or plume, region and not the actual flame. The vortex rollup process can be delayed by increasing either the Froude (Fr) or Reynolds (Re) numbers. The shortest rollup length is for the flame corresponding to the lowest values of Fr and Re. Detailed numerical simulations of analogous counterflow flames were performed using a more detailed chemical mechanism for the sake of comparison.

• OSTI ID: 543509
• Journal Information: Combustion and Flame, Journal Name: Combustion and Flame Journal Issue: 4 Vol. 111; ISSN CBFMAO; ISSN 0010-2180
• Country of Publication: United States
• Language: English

Related Subjects

03 NATURAL GAS
COMBUSTION KINETICS
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MATHEMATICAL MODELS
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REACTION INTERMEDIATES
UNSTEADY FLOW