The Effect of Buoyancy on Flickering in Diffusion Flames

Durox, Daniel; Tang, Yuhai; Villermaux, Emmanuel

doi:10.1080/00102209708935648

Cited by 59 publications

(64 citation statements)

References 24 publications

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“…As a result, flame temperature decreased, and the buoyant force became weaker, thus causing a lower flickering frequency due to the slower convection velocity. It has been reported that the oscillating frequency increased as P was increased under the sub-atmospheric condition, with a pressure exponent of 1/3 [5]. This conflicts with present results.…”

Section: Frequency and Amplitude Versus Primary Air Mass Flow Ratecontrasting

confidence: 57%

“…For 0.01 m injector exit diameter d, the calculated results are presented in Table 2. It can be found in Table 2 that the predicted values from all theoretical models fall within the range of measurement value, i.e., [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22] Hz. This implied that the puffing frequency of swirling flame was also concentrated on the low-frequency domain similar to that of non-swirl flame.…”

Section: Predicted Frequencies and Correlationsmentioning

confidence: 99%

“…It was also found that the oscillating amplitude have an analogous functional deviation with the gravity level. Durox et al [5] discovered that the correlation between gravity and the puffing frequency approaches f ∝ g 0.67 . Arai et al [6] ascribed the increasing of flickering frequency under higher gravitational levels to the increment in velocity of the wave and decline in wavelength.…”

Section: Introductionmentioning

confidence: 99%

“…The results showed that the oscillation frequency of flame is proportional to a power function of gravitational acceleration g as f ∝ g 0. 5 . It was also found that the oscillating amplitude have an analogous functional deviation with the gravity level.…”

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

An Experimental Investigation on Flame Pulsation for a Swirl Non-Premixed Combustion

et al. 2018

Energies

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Flame pulsation has a significant effect on combustion, and understanding its oscillatory behavior is important to the combustion community. An experiment was performed to analyze the pulsation characteristics of a swirl non-premixed flame under various parameters. The results showed that as fuel mass flow rate increased, the puffing frequency increased due to the decreased flame radiation fraction, and the puffing amplitude became smaller resulting in a more stable flame. With an increase in combustor pressure, the flickering frequency declined because of the increasing soot radiation, while the flickering amplitude uniformly increased, leading to more deteriorative flame stability. With an increment in mass flow rate of primary air, the puffing frequency decreased due to the enhanced mixing between fuel and primary air. Also, the puffing amplitude had an oscillating relationship with the mass flow rate of primary air. When the exit velocity of the injector was increased, the flickering frequency diminished nearly linearly because of the improving swirl intensity, and the flickering amplitude was approximately unaffected by injector exit velocity. Moreover, the measured puffing frequencies summarized over all cases varied within the range of 3-22 Hz, the predicted values from theoretical models based on non-swirl flame also fell within this range. The puffing frequency of swirl combustion was more sensitive to the variation in operating conditions than that of non-swirl combustion. Additionally, the obtained correlations indicated that the Strouhal number St was proportional to Fr −1.4 (the Froude number) and Re −2.9 (the Reynolds number), respectively.

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Section: Frequency and Amplitude Versus Primary Air Mass Flow Ratecontrasting

confidence: 57%

Section: Predicted Frequencies and Correlationsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

An Experimental Investigation on Flame Pulsation for a Swirl Non-Premixed Combustion

et al. 2018

Energies

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“…Durox et al (1997) investigated the flickering of jet diffusion flames and arrived at a different set of scaling relations. Tests were performed at varying pressure and at varying gravitational acceleration, which was achieved during parabolic flight tests.…”

Section: Cetegen and Ahmed (1993)mentioning

confidence: 99%

Cyclic flame propagation in premixed combustion

et al. 2013

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In experiments of hot surface ignition and subsequent flame propagation, a puffing flame instability is observed in mixtures that are stagnant and premixed prior to ignition. By varying the size of the hot surface, power input, and combustion vessel volume, it was determined that the instability is a function of the interaction of the flame, with the fluid flow induced by the combustion products rather than the initial plume established by the hot surface. Pressure ranges from 25 to 100 kPa and mixtures of n-hexane/air with equivalence ratios between φ = 0.58 and 3.0 at room temperature were investigated. Equivalence ratios between φ = 2.15 and 2.5 exhibited multiple flame and equivalence ratios above φ = 2.5 resulted in puffing flames at atmospheric pressure. The phenomenon is accurately reproduced in numerical simulations and a detailed flow field analysis revealed competition between the inflow velocity at the base of the flame and the flame propagation speed. The increasing inflow velocity, which exceeds the flame propagation speed, is ultimately responsible for creating a puff. The puff is then accelerated upward, allowing for the creation of the subsequent instabilities. The frequency of the puff is proportional to the gravitational acceleration and inversely proportional to the flame speed. A scaling relationship describes the dependence of the frequency on gravitational acceleration, hot surface diameter, and flame speed. This relation shows good agreement for rich n-hexane/air and lean hydrogen/air flames, as well as lean hexane/hydrogen/air mixtures.

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Effect of sub‐atmospheric pressures on buoyancy‐dominated hydrocarbon fuel fires: An experimental analysis on thermal flickering frequency

Tang

2021

Fire and Materials

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Summary Thermal flickering of a fire is caused by the buoyancy‐induced Kelvin‐Helmholtz‐type instability in the buoyant shear layer between burned gases and ambient air. The study of flickering frequency and inherent buoyancy‐induced instability are of great importance for fire essential parameters and their applications like fire detection, burner, and furnace designs. The flickering frequency of hydrocarbon fuel fires involved methane, ethylene, and propane was studied at low pressures ranging from 0.03 to 0.1 MPa. Three different fuel flow rates were configured for each fuel type of diffusion flame. Generally, the flickering behaviors were observed falling into three regimes: tip flickering, intermittent flickering, and continuous flickering. The continuous flickering appeared when the fuel flow rate or pressure increased above a particular level. The observed thermal flickering frequency varied from about 8 Hz at 0.03 MPa to 12 Hz at 0.1 MPa and was found insensitive to fuel type and flow rate. Thermal flickering frequency increased with the increasing of pressure with a power of 0.27. Buoyancy force dominates the flame flicking behavior under a wide range of sub‐atmospheric pressures and fuel exit velocities. In addition, multiple frequencies phenomenon was observed in the tests.

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The Effect of Buoyancy on Flickering in Diffusion Flames

Cited by 59 publications

References 24 publications

An Experimental Investigation on Flame Pulsation for a Swirl Non-Premixed Combustion

An Experimental Investigation on Flame Pulsation for a Swirl Non-Premixed Combustion

Cyclic flame propagation in premixed combustion

Effect of sub‐atmospheric pressures on buoyancy‐dominated hydrocarbon fuel fires: An experimental analysis on thermal flickering frequency

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