Response of counterflow diffusion flames to oscillating strain rates

Im, Hong G.; Law, Chung K.; Kim, J. S.; Williams, Forman A.

doi:10.1016/0010-2180(94)00059-2

Cited by 79 publications

(42 citation statements)

References 6 publications

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“…5. These time-delay (or phase-lag) effects should be especially significant near extinction conditions when the flame exhibits the greatest sensitivity [18]. Third, time-history effects need to be accounted for to arrive at the appropriate definition of the local scalar dissipation rate and its fluctuations.…”

Section: Implications For Turbulent Combustionmentioning

confidence: 99%

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Vortex-induced extinction behavior in methanol gaseous flames: A comparison with quasi-steady extinction

Santoro

Kyritsis

Liñán

et al. 2000

Proceedings of the Combustion Institute

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Using a combination of HCHO planar laser-induced fluorescence and laser Doppler velocimetry measurements, the extinction behavior of methanol counterflow diffusion flames was examined experimentally under conditions in which the extinction was brought about by a vortex generated on the oxidizer side. Comparisons were made with quasi-steady extinction results for the same flames. It was found that the flames can withstand instantaneous strain rates as much as two-and-a-half times larger than the quasisteady ones. The finding was rationalized phenomenologically by comparing the characteristic times of the problem, that is, the mechanical time, the chemical time, and the vortex turnover time. Specifically, estimates of these times yielded the following ordering: s ch Ͻ s vort Ͻ s m . As a result, the vortex introduced an unsteady effect in the outer diffusive-convective layer of the flame, while the inner reactive-diffusive layer behaved in a quasi-steady manner. Consequently, the flame was subject to a damped strain rate through the outer layer. Results from a simple analytical model showed that the difference between vortexinduced extinction and quasi-steady extinction was much more modest in terms of instantaneous scalar dissipation rate or Damkö hler number. Furthermore, the temporal history of the strain rate was found to be necessary to determine the effective strain rate felt by the flame. Implications of these findings for turbulent diffusion flame modeling by the flamelet approach are discussed.

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Section: Implications For Turbulent Combustionmentioning

confidence: 99%

“…Transient effects have been studied for some time and were first introduced in a partly analytical, partly experimental investigation [11]. In subsequent years, a number of computational [12][13][14][15] and analytical [16][17][18] studies followed. Most pertinent is a systematic analysis of flame extinction in Ref.…”

Section: Introductionmentioning

confidence: 99%

Vortex-induced extinction behavior in methanol gaseous flames: A comparison with quasi-steady extinction

Santoro

Kyritsis

Liñán

et al. 2000

Proceedings of the Combustion Institute

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“…Lean CH 4 -flames subject to time-dependent perturbations of the strain rate are investigated in [2], focussing on the time delay between perturbation and flame response as well as the amplitude of the flame response due to different perturbation frequencies. Oscillating strain rates are also investigated in [3] by using large activation energy asymptotics to analyse the response behaviour of a counterflow diffusion flame. Fleifil et al [4] describes the response of a laminar premixed flame stabilized on the rim of a tube subjected to flow oscillations and develops a model which captures the flame surface kinematics.…”

mentioning

confidence: 99%

Investigation of the Dynamical Response of Methane/Air Counterflow Flames to Inflow Mixture Composition and Flow Field Perturbations

König

Bykov

Maas

2008

Flow Turbulence Combust

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This work presents an analysis of the response of laminar, stretched, premixed CH 4 -air counterflow flames subject to periodical perturbations of the inflow mixture composition and the flow field in the context of ILDM and REDIM. Investigations of the perturbation propagation show, that the perturbation reaches the flame under certain conditions only; changes of the perturbation due to dissipative processes are investigated. Different methods are applied to gain an in-depth view of the influence of the perturbation on the chemical kinetics, namely correlation analyses of species in state space and timescale and element composition analyses. For the timescale analyses, two methods are applied, the ILDM method and a new concept for timescale analysis within the REDIM method. It is shown, that the perturbation does not change the global behaviour of the chemical kinetics and it is suggested to apply REDIMs for a low-dimensional description of perturbed flames.

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“…Although our applied objective is to understand key physical/chemical flameholding processes in hydrocarbon-fueled airbreathing scramjets (see [22] for a detailed review of flameholding processes and ground-test effects), such engines represent but one of many different applications that may be affected. Despite the surge of interest in unsteady flames during the early 1990's [3][4][5][6][7][8][9][10][11][12][13][14][15], much remains to be understood regarding specific physical/chemical effects of acoustic oscillations on the structure and extinction of even the simplest dynamically strained diffusion flames. Most of the current knowledge stems from large-activation-energy asymptotic analyses [6,8,9] and numerical simulations [5,7,11,12].…”

Section: Introductionmentioning

confidence: 99%

“…Despite the surge of interest in unsteady flames during the early 1990's [3][4][5][6][7][8][9][10][11][12][13][14][15], much remains to be understood regarding specific physical/chemical effects of acoustic oscillations on the structure and extinction of even the simplest dynamically strained diffusion flames. Most of the current knowledge stems from large-activation-energy asymptotic analyses [6,8,9] and numerical simulations [5,7,11,12]. The few known experimental studies have emphasized detailed nonintrusive measurements of species, temperature, and velocity, and resultant axial strain rates in methane-air and propane-air systems at relatively low frequencies [10,[13][14][15].…”

Section: Introductionmentioning

confidence: 99%

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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Response of counterflow diffusion flames to oscillating strain rates

Cited by 79 publications

References 6 publications

Vortex-induced extinction behavior in methanol gaseous flames: A comparison with quasi-steady extinction

Vortex-induced extinction behavior in methanol gaseous flames: A comparison with quasi-steady extinction

Investigation of the Dynamical Response of Methane/Air Counterflow Flames to Inflow Mixture Composition and Flow Field Perturbations

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

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