scholarly journals The study of the turbulent burning velocity by imaging the wrinkled flame surface

2002 ◽  
Author(s):  
S. Filatyev ◽  
J. Driscoll ◽  
C. Carter ◽  
J. Donbar
Keyword(s):  
Burning Velocity ◽  
Flame Surface ◽  
Wrinkled Flame ◽  
Turbulent Burning Velocity

The turbulent burning velocity for large-scale and small-scale turbulence

1999 ◽  
Vol 384 ◽  
pp. 107-132 ◽  
Author(s):  
N. PETERS
Keyword(s):  
Level Set ◽  
Reaction Zone ◽  
Large Scale ◽  
Burning Velocity ◽  
Small Scale ◽  
Constant Density ◽  
Flame Surface ◽  
Reaction Zones ◽  
Scale Turbulence ◽  
Turbulent Burning Velocity

The level-set approach is applied to a regime of premixed turbulent combustion where the Kolmogorov scale is smaller than the flame thickness. This regime is called the thin reaction zones regime. It is characterized by the condition that small eddies can penetrate into the preheat zone, but not into the reaction zone.By considering the iso-scalar surface of the deficient-species mass fraction Y immediately ahead of the reaction zone a field equation for the scalar quantity G(x, t) is derived, which describes the location of the thin reaction zone. It resembles the level-set equation used in the corrugated flamelet regime, but the resulting propagation velocity s*L normal to the front is a fluctuating quantity and the curvature term is multiplied by the diffusivity of the deficient species rather than the Markstein diffusivity. It is shown that in the thin reaction zones regime diffusive effects are dominant and the contribution of s*L to the solution of the level-set equation is small.In order to model turbulent premixed combustion an equation is used that contains only the leading-order terms of both regimes, the previously analysed corrugated flamelets regime and the thin reaction zones regime. That equation accounts for non-constant density but not for gas expansion effects within the flame front which are important in the corrugated flamelets regime. By splitting G into a mean and a fluctuation, equations for the Favre mean [Gtilde]and the variance [Gtilde]″2 are derived. These quantities describe the mean flame position and the turbulent flame brush thickness, respectively. The equation for [Gtilde]″2 is closed by considering two-point statistics. Scaling arguments are then used to derive a model equation for the flame surface area ratio [rhotilde]. The balance between production, kinematic restoration and dissipation in this equation leads to a quadratic equation for the turbulent burning velocity. Its solution shows the ‘bending’ behaviour of the turbulent to laminar burning velocity ratio sT/sL, plotted as a function of v′/sL. It is shown that the bending results from the transition from the corrugated amelets to the thin reaction zones regimes. This is equivalent to a transition from Damköhler's large-scale to his small-scale turbulence regime.

Turbulent burning velocity, burned gas distribution, and associated flame surface definition

2003 ◽  
Vol 133 (4) ◽  
pp. 415-430 ◽  
Author(s):  
D. Bradley ◽  
M.Z. Haq ◽  
R.A. Hicks ◽  
T. Kitagawa ◽  
M. Lawes ◽  
...  
Keyword(s):  
Burning Velocity ◽  
Flame Surface ◽  
Gas Distribution ◽  
Turbulent Burning Velocity

An Analysis of Local Quantities of Turbulent Premixed Flames Using DNS Databases

2007 ◽  
Author(s):  
Kazuya Tsuboi ◽  
Shinnosuke Nishiki ◽  
Tatsuya Hasegawa
Keyword(s):  
Reaction Rate ◽  
Burning Velocity ◽  
Turbulent Flame ◽  
Premixed Flames ◽  
Three Dimensional ◽  
Flame Surface ◽  
Turbulent Premixed Flames ◽  
Density Ratios ◽  
Turbulent Burning Velocity ◽  
Turbulent Premixed

An analysis of local flame area was performed using DNS (Direct Numerical Simulation) databases of turbulent premixed flames with different density ratios and with different Lewis numbers. Firstly, a local flame surface at a prescribed progress variable was identified as a local three-dimensional polygon. And then the polygon was divided into some triangles and local flame area was evaluated. The turbulent burning velocity was evaluated using the ratio of the area of turbulent flame to that of planar flame and compared with the turbulent burning velocity obtained by the reaction rate.

scholarly journals Burning Rates and Surface Characteristics of Hydrogen-Enriched Turbulent Lean Premixed Methane-Air Flames

2009 ◽  
Author(s):  
Hongsheng Guo ◽  
Badri Tayebi ◽  
Cedric Galizzi ◽  
Dany Escudie´
Keyword(s):  
Surface Area ◽  
Burning Velocity ◽  
Flame Structure ◽  
Surface Characteristics ◽  
Flame Surface ◽  
Laminar Burning Velocity ◽  
Hydrogen Addition ◽  
Lean Premixed ◽  
Burning Rates ◽  
Turbulent Burning Velocity

The burning rates and surface characteristics of hydrogen-enriched turbulent lean premixed methane-air flames were experimentally studied by laser tomography visualization method using a V-shaped flame configuration. Turbulent burning velocities were measured and the variation of flame surface characteristics due to hydrogen addition was analyzed. The results show that hydrogen addition causes an increase in turbulent burning velocity for lean CH4-air mixtures when the turbulent level in the unburned mixture is not changed. The increase rate of turbulent burning velocity is higher than that of the corresponding laminar burning velocity, suggesting that the increase in turbulent velocity due to hydrogen addition is caused by not only chemical kinetics effect, but also the variation in flame structure due to turbulence. The further analysis of flame surface characteristics and brush thickness indicate that hydrogen addition slightly decreases local flame surface density, but increases total flame surface area because of the increased flame brush thickness. As a result, turbulent burning velocity is intensified by the increase in total flame surface area and the increased laminar burning velocity, when hydrogen is added.

scholarly journals Reconciling turbulent burning velocity with flame surface area in small-scale turbulence

2018 ◽  
Vol 858 ◽  
Author(s):  
G. V. Nivarti ◽  
R. S. Cant ◽  
S. Hochgreb
Keyword(s):  
Burning Rate ◽  
Surface Area ◽  
Burning Velocity ◽  
Small Scale ◽  
Flame Surface ◽  
Additional Contribution ◽  
Individual Contributions ◽  
Scale Turbulence ◽  
Turbulence Length ◽  
Turbulent Burning Velocity

A discrepancy between the enhancement in overall burning rate and the enhancement in flame surface area measured for high-intensity turbulence is addressed. In order to reconcile the two quantities, an additional contribution from the effective turbulent diffusivity is considered. This contribution is expected to arise in sufficiently intense turbulence from eddies smaller than the flamelet thickness. In the present work, the enhancement in diffusivity arising from these eddies is estimated based on a model energy spectrum; individual contributions from all turbulence length scales smaller the flamelet thickness are integrated over the corresponding portion of the spectrum. It is shown that diffusivity enhancement, estimated in this manner, is able to account for the measured discrepancy between the overall burning rate enhancement and flame surface area enhancement. The factor quantifying this discrepancy is formalized as a closed-form function of the Karlovitz number.

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