Two-dimensional direct numerical simulation of opposed-jet hydrogen/air flames: Transition from a diffusion to an edge flame

Lee, J.; Frouzakis, Christos E.; Boulouchos, Konstantinos

doi:10.1016/s0082-0784(00)80283-0

Cited by 18 publications

(5 citation statements)

References 28 publications

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“…To investigate the edge responses in more realistic situations, numerical simulations of the nonpremixed edge flames have been performed as a flame-vortex interaction with simple chemistry [10,11], in a counterflow configuration with hydrogen-air chemistry [12,13], as a steady propagation with methanol-air chemistry [14], and as a transient ignition front dynamics with hydrogenair chemistry [15,16]. Throughout these detailed simulation studies, consideration of the realistic effects resulted in difficulties in unique determination of the edge flame speed in terms of a few simple physical parameters.…”

Section: Introductionmentioning

confidence: 99%

“…In particular, in contrast to the theoretical prediction [7], the existence of negative edge flame speed was hardly found in direct simulation studies, with a few exceptions [15,16] in which a negative flame speed was observed during the phase of intense interaction with the flame edge and counter-rotating vortices. Furthermore, the effects of flow transients leading to a wide variation in the edge flame dynamics have been noted [10][11][12][13]15,16].…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Transient dynamics of edge flames in a laminar nonpremixed hydrogen–air counterflow

Yoo

2005

Proceedings of the Combustion Institute

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Transient dynamics of edge flames in a laminar nonpremixed hydrogen–air counterflow

Yoo

2005

Proceedings of the Combustion Institute

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“…It was concluded that flame restoration occurs as a velocity-limited piloted-reignition along a thin stagnated region containing inter-diffused jet flows; or, when the inward "stretched laminar burning velocity" finally exceeds the maximum outward radial velocity [21]. Recent very detailed numerical simulations [23,24,28] fully support our earlier simplified description. Note, for extinction-restoration hysteresis, the radial strain rate in the central stagnation region must always be smaller than that required for extinction.…”

Section: Steady State Flame Strength Measurementsmentioning

confidence: 70%

Dynamic Weakening (Extinction) of Simple Hydrocarbon-Air Counterflow Diffusion Flames by Oscillatory Inflows

Pellett¹,

Kabaria²,

Panigrahi³

et al. 2005

41st AIAA/ASME/SAE/ASEE Joint Propulsion Conference &Amp;amp; Exhibit

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This study of laminar non-premixed HC-air flames used an Oscillatory-input Opposed Jet Burner (OOJB) system developed from a previously well-characterized 7.2-mm Pyrex-nozzle OJB system. Over 600 dynamic Flame Strength (FS) measurements were obtained on unanchored (free-floating) laminar Counterflow Diffusion Flames (CFDF's). Flames were stabilized using plug inflows having steady-plus-sinusoidal axial velocities of varied magnitude, frequency, f, up to 1600 Hz, and phase angle from 0 (most data) to 360 degrees. Dynamic FS is defined as the maximum average air input velocity (U air , at nozzle exit) a CFDF can sustain before strain-induced extinction occurs due to prescribed oscillatory "peak-to-peak" velocity inputs superimposed on steady inputs.Initially, dynamic flame extinction data were obtained at low f, and were supported by 25-120 Hz HotWire cold-flow velocity data at nozzle exits. Later, expanded extinction data were supported by 4-1600 Hz Probe Microphone (PM) pk/pk P data at nozzle exits. The PM data were first obtained without flows, and later with cold stagnating flows, which better represent speaker-diaphragm dynamics during runs. The PM approach enabled characterizations of Dynamic Flame Weakening (DFW) of CFDF's from 8 to 1600 Hz. DFW was defined as % decrease in FS per Pascal of pk/pk P oscillation, namely, DFW = -100 d(U air / U air,0Hz ) / d(pkpk P). The linear normalization with respect to acoustic pressure magnitude (and steady state (SS) FS) led to a DFW unaffected by strong internal resonances.For the C 2 H 4 /N 2 -air system, from 8 to 20 Hz, DFW is constant at 8.52 + 0.20 (% weakening)/Pa. This reflects a "quasi-steady flame response" to an acoustically induced dU air /dP. Also, it is surprisingly independent of C 2 H 4 /N 2 mole fraction due to normalization by SS FS. From 20 to ~ 150 Hz, the C 2 H 4 /N 2 -air flames weakened progressively less, with an inflection at ~ 70 Hz, and became asymptotically insensitive (DFW ~ 0) at ~ 300 Hz, which continued to 1600 Hz. The DFW of CH 4 -air flames followed a similar pattern, but showed much greater weakening than C 2 H 4 /N 2 -air flames; i.e., the quasi-steady DFW (8 to ~ 15 Hz) was 44.3 %/Pa, or ~ 5x larger, even though the 0 Hz (SS) FS was only 3.0 x smaller. The quasi-steady DFW's of C 3 H 8 -air and C 2 H 6 -air were intermediate at 34.8 and 20.9 %Pa, respectively. The DFW profiles of all four fuels, at various frequencies, correlated well but non-linearly with respective SS FS's. Notably, the DFW profile for C 3 H 8 -air fell more rapidly in the range > 15 to 60 Hz, compared with the 1-and 2-carbon fuels. This may indicate a shift in chemical kinetics, and/or O 2 transport to a flame that moved closer to the fuel-side.

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“…The temporal evolution of their topological structures were numerically described for a flame disk, which is a small burning element serving as an ignition source to reignite the extinguished area in turbulent flame, and flame hole at high strain rate flames . The existence of multiple solutions of vigorously burning flames at identical conditions was displayed when there is no inert gas flow curtain; a disk diffusion flame and an edge flame at appropriately high strain flames . In recent years numerous numerical works have been devoted to the study of such local extinction and reignition events in turbulent diffusion flames using flamelet modeling. , A variety of research efforts have also been focused on clarifying the dynamic aspects of edge flame. − However most of these researches have been focused on the responses of a flame hole at high strain rate flames.…”

Section: Introductionmentioning

confidence: 99%

A Study on Flame Extinction Characteristics along a C-Curve

et al. 2009

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A study has been conducted both experimentally and numerically to clarify impacts of curtain flow and velocity ratio on low strain rate flame extinction and to further display transition of shrinking flame disk to flame-hole. Critical mole fractions at flame extinction are provided in terms of velocity ratio, nitrogen curtain flow rate, and global strain rate. Flame extinction modes are grouped into four on a C-curve, which is characterized by a flame-hole, the shrinking of edge flame, and edge flame oscillation. It is seen that varying curtain flow rate does not impact on edge flame oscillation, flame extinction, and even flame extinction modes. Variation of velocity ratio extends to the low strain rate flame extinction modes beyond the turning point. It is found that the expanding and shrinking flames always have negative flame propagation speed; it is also recognized that the decrease of flame radius is prone to extinguish due to the dominant role of radial conduction heat loss. The examination of energy fraction is also presented to stress the role of radial conduction heat loss, particularly at the outer flame edge part.

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Two-dimensional direct numerical simulation of opposed-jet hydrogen/air flames: Transition from a diffusion to an edge flame

Cited by 18 publications

References 28 publications

Transient dynamics of edge flames in a laminar nonpremixed hydrogen–air counterflow

Transient dynamics of edge flames in a laminar nonpremixed hydrogen–air counterflow

Dynamic Weakening (Extinction) of Simple Hydrocarbon-Air Counterflow Diffusion Flames by Oscillatory Inflows

A Study on Flame Extinction Characteristics along a C-Curve

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