Role of Darrieus–Landau instability in propagation of expanding turbulent flames

2018 ◽  
Vol 850 ◽  
pp. 784-802 ◽  
Author(s):  
Sheng Yang ◽  
Abhishek Saha ◽  
Zirui Liu ◽  
Chung K. Law
Keyword(s):  
Flame Front ◽  
Flame Propagation ◽  
High Pressures ◽  
Turbulent Flame ◽  
Turbulent Flames ◽  
Scaling Analysis ◽  
Turbulent Eddies ◽  
Front Instability ◽  
Cellular Flame

In this paper we study the essential role of Darrieus–Landau (DL), hydrodynamic, cellular flame-front instability in the propagation of expanding turbulent flames. First, we analyse and compare the characteristic time scales of flame wrinkling under the simultaneous actions of DL instability and turbulent eddies, based on which three turbulent flame propagation regimes are identified, namely, instability dominated, instability–turbulence interaction and turbulence dominated regimes. We then perform experiments over an extensive range of conditions, including high pressures, to promote and manipulate the DL instability. The results clearly demonstrate the increase in the acceleration exponent of the turbulent flame propagation as these three regimes are traversed from the weakest to the strongest, which are respectively similar to those of the laminar cellularly unstable flame and the turbulent flame without flame-front instability, and thus validating the scaling analysis. Finally, based on the scaling analysis and the experimental results, we propose a modification of the conventional turbulent flame regime diagram to account for the effects of DL instability.

The Effect of Lewis Number on Instantaneous Flamelet Speed and Position Statistics in Counter-Flow Flames With Increasing Turbulence

2017 ◽  
Author(s):  
Sean D. Salusbury ◽  
Ehsan Abbasi-Atibeh ◽  
Jeffrey M. Bergthorson
Keyword(s):  
Flame Front ◽  
Turbulence Intensity ◽  
High Speed ◽  
Rayleigh Scattering ◽  
Turbulent Flame ◽  
Lewis Number ◽  
Turbulent Flames ◽  
Flame Speed ◽  
Laminar Flames ◽  
Counter Flow

Differential diffusion effects in premixed combustion are studied in a counter-flow flame experiment for fuel-lean flames of three fuels with different Lewis numbers: methane, propane, and hydrogen. Previous studies of stretched laminar flames show that a maximum reference flame speed is observed for mixtures with Le ≳ 1 at lower flame-stretch values than at extinction, while the reference flame speed for Le ≪ 1 increases until extinction occurs when the flame is constrained by the stagnation point. In this work, counter-flow flame experiments are performed for these same mixtures, building upon the laminar results by using variable high-blockage turbulence-generating plates to generate turbulence intensities from the near-laminar u′/SLo=1 to the maximum u′/SLo achievable for each mixture, on the order of u′/SLo=10. Local, instantaneous reference flamelet speeds within the turbulent flame are extracted from high-speed PIV measurements. Instantaneous flame front positions are measured by Rayleigh scattering. The probability-density functions (PDFs) of instantaneous reference flamelet speeds for the Le ≳ 1 mixtures illustrate that the flamelet speeds are increasing with increasing turbulence intensity. However, at the highest turbulence intensities measured in these experiments, the probability seems to drop off at a velocity that matches experimentally-measured maximum reference flame speeds in previous work. In contrast, in the Le ≪ 1 turbulent flames, the most-probable instantaneous reference flamelet speed increases with increasing turbulence intensity and can, significantly, exceed the maximum reference flame speed measured in counter-flow laminar flames at extinction, with the PDF remaining near symmetric for the highest turbulence intensities. These results are reinforced by instantaneous flame position measurements. Flame-front location PDFs show the most probable flame location is linked both to the bulk flow velocity and to the instantaneous velocity PDFs. Furthermore, hydrogen flame-location PDFs are recognizably skewed upstream as u′/SLo increases, indicating a tendency for the Le ≪ 1 flame brush to propagate farther into the unburned reactants against a steepening average velocity gradient.

The role of low temperature fuel chemistry on turbulent flame propagation

2014 ◽  
Vol 161 (2) ◽  
pp. 475-483 ◽  
Author(s):  
Sang Hee Won ◽  
Bret Windom ◽  
Bo Jiang ◽  
Yiguang Ju
Keyword(s):  
Low Temperature ◽  
Flame Propagation ◽  
Turbulent Flame

scholarly journals Role of Low-Temperature Fuel Chemistry on Turbulent Flame Propagation

2019 ◽  
Vol 35 (2) ◽  
pp. 158-166
Author(s):  
Fan ZHANG ◽  
◽  
Zhe REN ◽  
Shenghui ZHONG ◽  
Mingfa YAO ◽  
...  
Keyword(s):  
Low Temperature ◽  
Flame Propagation ◽  
Turbulent Flame

Extreme role of preferential diffusion in turbulent flame propagation

2018 ◽  
Vol 188 ◽  
pp. 498-504 ◽  
Author(s):  
Sheng Yang ◽  
Abhishek Saha ◽  
Wenkai Liang ◽  
Fujia Wu ◽  
Chung K. Law
Keyword(s):  
Flame Propagation ◽  
Turbulent Flame ◽  
Preferential Diffusion

Large-Scale Homogeneous Hydrogen-Air-Steam Deflagration Experiment Simulated Using Two Turbulent Flame Speed Closure Models

2016 ◽  
Author(s):  
Tadej Holler ◽  
Varun Jain ◽  
Ed M. J. Komen ◽  
Ivo Kljenak
Keyword(s):  
Flame Propagation ◽  
Nuclear Power ◽  
Large Scale ◽  
Turbulent Flame ◽  
Turbulent Flames ◽  
Flame Speed ◽  
Energy Output ◽  
Combustion Model ◽  
Turbulent Flame Speed ◽  
Combustion Models

The CFD combustion modeling approach based on two combustion models was applied to a hydrogen deflagration experiment conducted in a large-scale confined experimental vessel. The used combustion models were Zimont’s Turbulent Flames Speed Closure (TFC) model and Lipatnikov’s Flame Speed Closure (FSC) model. The conducted simulations are aimed to aid identifying and evaluating the potential hydrogen risks in Nuclear Power Plant (NPP) containment. The simulation results show good agreement with experiment for axial flame propagation using the Lipatnikov combustion model. However substantial overprediction in radial flame propagation is observed using both combustion models, which consequently results also in overprediction of the pressure increase rate and overall combustion energy output. As assumed for a large-scale experiment without any turbulence inducing structures, the combustion took place in low-turbulence regimes, where the Lipatnikov combustion model, due to its inclusion of quasi-laminar source term, has advantage over the Zimont model.

Effect of Centrifugal Force on Turbulent Premixed Flames

2014 ◽  
Vol 137 (1) ◽  
Author(s):  
Alejandro M. Briones ◽  
Balu Sekar ◽  
Timothy Erdmann
Keyword(s):  
Numerical Model ◽  
Flame Front ◽  
Centrifugal Force ◽  
Flame Propagation ◽  
Propagation Velocity ◽  
Turbulent Flame ◽  
Premixed Flames ◽  
Turbulent Premixed Flames ◽  
Flame Propagation Velocity ◽  
Turbulent Flame Speed

The effect of centrifugal force on flame propagation velocity of stoichiometric propane–, kerosene–, and n-octane–air turbulent premixed flames was numerically examined. The quasi-turbulent numerical model was set in an unsteady two-dimensional (2D) geometry with finite length in the transverse and streamwise directions but with infinite length in the spanwise direction. There was relatively good comparison between literature-reported measurements and predictions of propane–air flame propagation velocity as a function of centrifugal force. It was found that for all mixtures the flame propagation velocity increases with centrifugal force. It reaches a maximum, then falls off rapidly with further increases in centrifugal force. The results of this numerical study suggest that there are no distinct differences among the three mixtures in terms of the trends seen of the effect of centrifugal force on the flame propagation velocity. There are, however, quantitative differences. The numerical model is set in a noninertial, rotating reference frame. This rotation imposes a radially outward (centrifugal) force. The ignited mixture at one end of the tube raises the temperature and its heat release tends to laminarize the flow. The attained density difference combined with the direction of the centrifugal force promotes Rayleigh–Taylor instability. This instability with thermal expansion and turbulent flame speed constitute the flame propagation mechanism towards the other tube end. A wave is also generated from the ignition zone but propagates faster than the flame. During propagation the flame interacts with eddies that wrinkle and/or corrugate the flame. The flame front wrinkles interact with streamtubes that enhance Landau–Darrieus (hydrodynamic) instability, giving rise to a corrugated flame. Under strong stretch conditions the stabilizing equidiffusive-curvature mechanism fails and the flame front breaks up, allowing inflow of unburned mixture into the flame. This phenomenon slows down the flame temporarily and then the flame speeds up faster than before. However, if corrugation is large and the inflow of unburned mixture into the flame is excessive, the latter locally quenches and slows down the flame. This occurs when the centrifugal force is large, tending to blowout the flame. The wave in the tube interacts continuously with the flame through baroclinic torques at the flame front that further enhances the above mentioned flame–eddy interactions. Only at low centrifugal forces, the wave intermingles several times with the flame before the averaged flame propagation velocity is determined. The centrifugal force does not substantially increase the turbulent flame speed as commented by previous experimental investigations. The results also suggest that an ultracompact combustor (UCC) with high-g cavity (HGC) will be limited to centrifugal force levels in the 2000–3000 g range.

Experimental Study of Flame Stretch Under Engine-Like Conditions

2017 ◽  
Author(s):  
Behdad Afkhami ◽  
Yanyu Wang ◽  
Scott A. Miers ◽  
Jeffrey D. Naber
Keyword(s):  
Flame Front ◽  
Flame Propagation ◽  
High Speed ◽  
Combustion Engine ◽  
Turbulent Flame ◽  
Experimental Studies ◽  
Flame Velocity ◽  
Turbulent Flame Speed ◽  
Stretch Rate ◽  
Flame Stretch

Since fossil fuels will remain the main source of energy for power generation and transportation in next decades, their combustion processes remain an important concern for the foreseeable future. For liquid or gaseous fuels, flame velocity that propagates normal to itself and relative to the flow into the unburned mixture is one of the most important quantities to study. In a non-uniform flow, a curved flame front area changes continually which is known as flame stretch. The concept becomes more important when it is realized that the stretch affects the turbulent flame speed. The current research empirically studies flame stretch under engine-like conditions since there has not been enough experimental studies in this area. For this reason, a one-cylinder, direct-injection, spark-ignition, naturally-aspirated optical engine was utilized to image the flame propagation process inside an internal combustion engine cylinder on the tumble plane. The flame front was found by processing high speed images which were taken from the flame inside the cylinder. Flame front propagation analysis showed that after the flame kernel was developed, during flame propagation period, the stretch rate decreased until the flame front touches the piston surface. This trend was common among stoichiometric, lean, and rich mixtures. In addition, the fuel-air mixture with λ = 0.85 showed lower stretch rate compared to stoichiometric or lean mixture with λ = 1.2. However, based on previous studies, further enrichment may result in the flame stretch rate become greater than that of the stretch rates for stoichiometric or lean mixtures. Also, comparing the stretch rate at two different engine speeds revealed that as the speed increased the stretch rate also increased; especially during the early flame development period. Therefore, according to previous studies which discussed flame stretch as a mechanism for flame extinguishment, the probability of the flame extinction is higher when the engine speed is higher.

Effect of Centrifugal Force on Conventional and Alternative Fuel Surrogate Turbulent Premixed Flames

2014 ◽  
Author(s):  
Alejandro M. Briones ◽  
Balu Sekar ◽  
Timothy Erdmann
Keyword(s):  
Flame Front ◽  
Centrifugal Force ◽  
Flame Propagation ◽  
Propagation Velocity ◽  
Turbulent Flame ◽  
Premixed Flames ◽  
Flame Speed ◽  
Turbulent Premixed Flames ◽  
Flame Propagation Velocity ◽  
Turbulent Flame Speed

The effect of centrifugal force on flame propagation velocity of stoichiometric propane-, kerosene-, and n-octane-air turbulent premixed flames was numerically examined. The quasi-turbulent numerical model was set in an unsteady two-dimensional geometry with finite length in the transverse and streamwise directions but with infinite length in the spanwise direction. There was relatively good comparison between literature-reported measurements and predictions of propane-air flame propagation velocity as a function of centrifugal force. It was found that for all mixtures the flame propagation velocity increases with centrifugal force. It reaches a maximum then falls off rapidly with further increases in centrifugal force. The results of this numerical study suggest there are no distinct differences among the three mixtures in terms of the effect of centrifugal force on the flame propagation velocity. There are, however, quantitative differences. The numerical models are set in a non-inertial, rotating reference frame. This rotation imposes a radially outward (centrifugal) force. The ignited mixture at one end of the tube raises the temperature and its heat release tends to laminarize the flow. The attained density difference combined with the direction of the centrifugal force promotes Rayleigh-Taylor instability. This instability with thermal expansion and turbulent flame speed constitute the flame propagation mechanism towards the other tube end. A wave is also originated but propagates faster than the flame. During propagation the flame interacts with eddies that wrinkle and/or corrugate the flame. The flame front wrinkles interact with streamtubes that enhance Landau-Darrieus (hydrodynamic) instability, giving rise to a corrugated flame. Under strong stretch conditions the stabilizing equidiffusive-curvature mechanism fails and the flame front breaks up, allowing inflow of unburned mixture into the flame. This phenomenon slows down the flame temporarily and then the flame speeds up faster than before. However, if corrugation is large and the inflow of unburned mixture into the flame is excessive, the latter locally quenches and slows down the flame. This occurs when the centrifugal force is large, tending to blowout the flame. The wave in the tube interacts continuously with the flame through baroclinic torques at the flame front that further enhances the above mentioned flame-eddies interactions. Only at low centrifugal forces the wave intermingles several times with the flame before the averaged flame propagation velocity is determined. The centrifugal force does not substantially increase the turbulent flame speed as commented by previous experimental investigations. The results also suggest that an ultra-compact combustor (UCC) with high-g cavity (HGC) will be limited to centrifugal force levels in the 2000–3000g range.

Lean Premixed Turbulent Flame Front Structure and Implications for Modeling

2010 ◽  
Author(s):  
Frank T. C. Yuen ◽  
O¨mer L. Gu¨lder
Keyword(s):  
Flame Front ◽  
Turbulent Flame ◽  
Turbulent Flames ◽  
Experimental Conditions ◽  
Flame Thickness ◽  
Premixed Turbulent Combustion ◽  
Wide Range ◽  
Significant Difference ◽  
Lean Premixed ◽  
Front Curvature

Premixed turbulent flames of methane-air and propane-air stabilized on a Bunsen type burner were studied to investigate the structure of the flame front at a wide range of turbulence intensities covering the range of interest in lean premixed combustors. The flame front data were obtained using planar Rayleigh imaging, and particle image velocimetry was used to measure instantaneous velocity field for the experimental conditions studied. The fuel-air equivalence ratio range was from lean 0.6 to stoichiometric for methane flames, and from 0.7 to stoichiometric for propane flames. The non-dimensional turbulent rms velocity, u′/SL, covered a range from 3 to 24. Flame front thickness and flame front curvature statistics were obtained from 2D measurements. Flame front thickness increased slightly with increasing non-dimensional turbulence rms velocity in both methane and propane flames, although the flame thickening was more prominent in propane flames. There was not any significant difference in flame thickening whether the flame thickness is evaluated at progress variable 0.5, corresponding to the reaction zone, or 0.3, corresponding to the preheat zone. Variations of front curvature and flame thickness are presented for different premixed combustion regimes and implications of these findings for modelling premixed turbulent combustion are discussed.

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