The influence of laminar burning velocity on the structure and propagation of turbulent flames

1979 ◽  
Vol 367 (1731) ◽  
pp. 485-502 ◽  
Keyword(s):  
Turbulence Intensity ◽  
Burning Velocity ◽  
Diffusion Mechanism ◽  
Turbulent Flames ◽  
Laminar Burning Velocity ◽  
Premixed Turbulent Flames ◽  
Region Model ◽  
High Turbulence ◽  
Model Region ◽  
Turbulent Burning Velocity

An experimental study of the influence of laminar burning velocity on the structure and propagation of duct-confined premixed turbulent flames has been carried out. Propane, acetylene and hydrogen were used as fuels to vary the laminar burning velocity in the range from 20 to 280 cm/s. These experiments fully verify the three region model (region 1: u ' < 2 S L , η > δ L ; region 2: u ' ≈ 2 S L , η ≈ δ L to η ≫ δ L ; region 3: u ' > 2 S L , η < δ L ) of turbulent flames proposed earlier by Ballal & Lefebvre. Since a large increase in the laminar burning velocity has a stabilizing influence it is possible to suppress the ‘instability’ of region 1 and the ‘eddy entrainment’ of region 3. The ‘turbulent diffusion’ mechanism then becomes solely dominant, and the flame shows a ‘jet-like’ behaviour. For such a flame (i) both the burning velocity and flame turbulence intensity are independent of scale, (ii) the equations developed by Karlovitz and Ballal for regions of stable combustion accurately predict all the experimental data on turbulent burning velocity and flame turbulence, respectively, and (iii) the laminar burning velocity remains an important parameter of flame propagation even at very high turbulence intensity. Finally the important role of shear-generated turbulence and the ability of the flame either to dampen or to generate additional turbulence has been fully confirmed.

Further development of the three-region model of a premixed turbulent flame I. Turbulent diffusion dominated region 2

1979 ◽  
Vol 368 (1733) ◽  
pp. 267-282 ◽  
Keyword(s):  
Turbulence Intensity ◽  
Burning Velocity ◽  
Turbulent Flame ◽  
Turbulent Energy ◽  
Variable Density ◽  
Turbulent Flames ◽  
Laminar Burning Velocity ◽  
Advection Term ◽  
Set Up ◽  
Premixed Turbulent Flame

A study of the balance equation for turbulent kinetic energy of a premixed turbulent flame has been carried out. Various parameters constituting each term have either been measured or have been calculated from previously measured values. Propane and hydrogen were used as fuels, and the turbulence intensity of the approach flow was varied. Thus, an energy balance of turbulence in a flame has been set up. These results show that increase in both approach turbulence intensity and laminar burning velocity reduce the ratio of production/dissipation in a flame. Thus the stabilizing influence of laminar burning velocity is fully confirmed. The turbulent convection term is found to remain substantially unaltered. The advection term, on the other hand, changes from a loss to a gain in the turbulent energy of the flame. Finally, it is shown that significant differences exist between a flame and a non-reactive variable density axisymmetric jet. These conclusions make the study of turbulent flames unique in that theories that do not accommodate their special features should either be modified or abandoned.

Technical Note: The importance of turbulence intensity, eddy size and flame size in spark ignited, premixed flame growth

1997 ◽  
Vol 211 (1) ◽  
pp. 83-86 ◽  
Author(s):  
D S-K Ting ◽  
M. D. Checkel
Keyword(s):  
Turbulence Intensity ◽  
Burning Velocity ◽  
Lewis Number ◽  
Technical Note ◽  
Premixed Flame ◽  
Mean Square ◽  
Laminar Burning Velocity ◽  
The Mean ◽  
Turbulent Burning Velocity ◽  
Velocity Turbulence

The effects of laminar burning velocity, turbulence intensity, flame size and eddy size on the turbulent burning velocity of a premixed growing flame were experimentally separated in a 125 mm cubical chamber with lean methane-air mixtures spark ignited at 1 atm and 300 K. The turbulence was up to 2 m/s with 1 to 4 mm Taylor microscale. For the near unity Lewis number and near zero Markstein number mixture considered here, the turbulent burning velocity, St, can be approximated as: St = Sl + Cd(r/λ)u′, where Sl is the laminar burning velocity, r is the mean flame radius, λ is the Taylor microscale, u′ is the root mean square (r.m.s.) turbulence intensity and Cd is a constant of the order 0.02.

Study of Thermo-Diffusive Effects on Iso-Octane/Air Flames at Fixed Turbulence Karlovitz Number

2011 ◽  
Author(s):  
Akihiro Hayakawa ◽  
Tomohiro Takeo ◽  
Yukito Miki ◽  
Yukihide Nagano ◽  
Toshiaki Kitagawa
Keyword(s):  
Equivalence Ratio ◽  
Burning Velocity ◽  
Turbulent Flame ◽  
Turbulent Flames ◽  
Laminar Burning Velocity ◽  
Markstein Number ◽  
Flame Stretch ◽  
The Mean ◽  
Diffusive Effects ◽  
Turbulent Burning Velocity

Spherically propagating laminar and turbulent flames were studied using iso-octane / air mixtures with and without dilution. The main purpose of this study is to clarify the influence of thermo-diffusive effects on the turbulent flames. In order to examine the thermo-diffusive effects solely by separating them from the effects of flame stretch, turbulent burning velocities were compared at constant flame stretch factors. The mean flame stretch factor acting on turbulent flame front may be represented by the turbulence Karlovitz number. Thus, turbulent explosions were carried out at fixed turbulence Karlovitz numbers. The ratio of turbulent burning velocity to unstretched laminar burning velocity increased with the equivalence ratio for non-diluted mixtures at fixed turbulence Karlovitz numbers. And this ratio for CO2 diluted mixtures was larger than N2 diluted mixtures. The Markstein number that denotes the sensitivity of the flame to thermo-diffusive effects depends on the equivalence ratio and diluents of the mixture. The ratio of turbulent burning velocity to unstretched laminar one increased with decreasing Markstein number. Especially, it changed stepwise around Markstein number of zero. However, the burning velocity ratios did not increase with increasing mixture pressure although the Markstein number decreased with pressure.

scholarly journals Effect of Stretch on Local Burning Velocity of Premixed Turbulent Flames

2007 ◽  
Vol 2 (2) ◽  
pp. 268-280 ◽  
Author(s):  
Masaya NAKAHARA ◽  
Hiroyuki KIDO ◽  
Takamori SHIRASUNA ◽  
Koichi HIRATA
Keyword(s):  
Burning Velocity ◽  
Turbulent Flames ◽  
Premixed Turbulent Flames ◽  
Local Burning

Numerical Modeling of Stationary But Developing Premixed Turbulent Flames

2006 ◽  
Author(s):  
Pratap Sathiah ◽  
Andrei N. Lipatnikov
Keyword(s):  
Bluff Body ◽  
Burning Velocity ◽  
Rectangular Channel ◽  
Turbulent Flame ◽  
Flame Stabilization ◽  
Turbulent Flames ◽  
Turbulent Diffusivity ◽  
Flame Thickness ◽  
Premixed Turbulent Flames ◽  
Premixed Turbulent Flame

A typical stationary premixed turbulent flame is the developing flame, as indicated by the growth of mean flame thickness with distance from flame-stabilization point. The goal of this work is to assess the importance of modeling flame development for RANS simulations of confined stationary premixed turbulent flames. For this purpose, submodels for developing turbulent diffusivity and developing turbulent burning velocity, which were early suggested by our group (FSC model) and validated for expanding spherical flames [4], have been incorporated into the so-called Zimont model of premixed turbulent combustion and have been implemented into the CFD package Fluent 6.2. The code has been run to simulate a stationary premixed turbulent flame stabilized behind a triangular bluff body in a rectangular channel using both the original and extended models. Results of these simulations show that the mean temperature and velocity fields in the flame are markedly affected by the development of turbulent diffusivity and burning velocity.

412 Influence of Markstein Number on Local Burning Velocity of Premixed Turbulent Flames

2005 ◽  
Vol 2005.58 (0) ◽  
pp. 145-146
Author(s):  
Masaya NAKAHARA ◽  
Hiroyuki KIDO ◽  
Kenshiro NAKASHIMA ◽  
Hideaki TAKAMOTO ◽  
Koichi HIRATA
Keyword(s):  
Burning Velocity ◽  
Turbulent Flames ◽  
Premixed Turbulent Flames ◽  
Markstein Number ◽  
Local Burning

A two-eddy theory of premixed turbulent flame propagation

1981 ◽  
Vol 301 (1457) ◽  
pp. 1-25 ◽  
Keyword(s):  
Experimental Data ◽  
Reynolds Number ◽  
Burning Velocity ◽  
Turbulent Flame ◽  
Experimental Measurements ◽  
Laminar Burning Velocity ◽  
Turbulent Reynolds Number ◽  
Theoretical Predictions ◽  
Premixed Turbulent Flame ◽  
Turbulent Burning Velocity

Available experimental data on the turbulent burning velocity of premixed gases are surveyed. There is discussion of the accuracy of experimental measurements and the means of ascertaining relevant turbulent parameters. Results are presented in the form of the variation of the ratio of turbulent to laminar burning velocities with the ratio of r.m.s. turbulent velocity to laminar burning velocity, for different ranges of turbulent Reynolds number. A two-eddy theory of burning is developed and the theoretical predictions of this approach, as well as those of others, are compared with experimentally measured values.

An Experimental Study on Properties of Local Burning Velocity for Hydrogen Added Hydrocarbon Premixed Turbulent Flames

2011 ◽  
Author(s):  
Masaya Nakahara ◽  
Koichi Murakami ◽  
Jun Hashimoto ◽  
Atsushi Ishihara
Keyword(s):  
Burning Velocity ◽  
Quantitative Relationship ◽  
Lewis Number ◽  
Turbulent Flames ◽  
Laminar Flames ◽  
Mean Values ◽  
Laser Tomography ◽  
Turbulence Condition ◽  
Turbulent Burning Velocity ◽  
Local Burning

This study is performed to investigate directly the local flame properties of turbulent propagating flames at the same weak turbulence condition (u′/SL0 = 1.4), in order to clarify basically the influence of the addition of hydrogen to methane or propane mixtures on its local burning velocity. The mixtures having nearly the same laminar burning velocity with different rates of addition of hydrogen δH are prepared. A two-dimensional sequential laser tomography technique is used to obtain the relationship between the flame shape and the flame displacement. The local flame displacement velocity SF is quantitatively obtained as the key parameters of the turbulent combustion. Additionally, the Markstein number Ma was obtained from outwardly propagating spherical laminar flames, in order to examine the effects of positive stretch and curvature on burning velocity. It was found that the trends of the mean values of measured SF with respect to δH, the total equivalence ratio Φ and fuel types corresponded well its turbulent burning velocity. The trend of the obtained Ma could explain the local burning velocity of turbulent flames only qualitatively. Based on the Ma, the local burning velocity at the part of turbulent flames with positive stretch and curvature, SLt, is estimated quantitatively. As a result, a quantitative relationship between the estimated SLt and the SF at positive stretch and curvature of turbulent flames could be observed for mixtures with increasing the Lewis number.

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