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

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.

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Flame stretch rate as a determinant of turbulent burning velocity

Philosophical Transactions of The Royal Society A Mathematical Physical and Engineering Sciences ◽

10.1098/rsta.1992.0012 ◽

1992 ◽

Vol 338 (1650) ◽

pp. 359-387 ◽

Cited By ~ 172

Keyword(s):

Burning Velocity ◽

Turbulent Flame ◽

Lewis Number ◽

Turbulent Flames ◽

Stretch Rate ◽

Dimensionless Groups ◽

Flame Stretch ◽

Experimental Values ◽

Turbulent Burning Velocity

A rational basis for correlating turbulent burning velocities is shown to involve the product of the Karlovitz stretch factor and the Lewis number. A generalized expression is derived to show how flame stretch is related to the velocity field. A new dimensionless correlation of experimental values of turbulent burning velocities is presented. Dimensionless groups also are used in correlations of laminar and turbulent flame extinction stretch rates. A distribution function of stretch rates in turbulent flames, based on an earlier one of Yeung et al ., is proposed and the experimental data are well predicted by a theory based on flamelet extinction by flame stretch with this distribution. Uncertainties arise concerning the role of negative stretch rate. Laminar flamelet modelling of complex combustion appears to have a broader validity than might be expected and some explanation for this is offered.

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A two-eddy theory of premixed turbulent flame propagation

Philosophical Transactions of the Royal Society of London. Series A, Mathematical and Physical Sciences ◽

10.1098/rsta.1981.0096 ◽

1981 ◽

Vol 301 (1457) ◽

pp. 1-25 ◽

Cited By ~ 83

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.

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

Proceedings of the Royal Society of London Series A - Mathematical and Physical Sciences ◽

10.1098/rspa.1979.0099 ◽

1979 ◽

Vol 367 (1731) ◽

pp. 485-502 ◽

Cited By ~ 13

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.

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

Proceedings of the Royal Society of London Series A - Mathematical and Physical Sciences ◽

10.1098/rspa.1979.0127 ◽

1979 ◽

Vol 368 (1733) ◽

pp. 267-282 ◽

Cited By ~ 4

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.

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Influence of Pressure on Markstein Number Effect in Turbulent Flame Front Propagation

Volume 1A: Combustion, Fuels and Emissions ◽

10.1115/gt2013-94307 ◽

2013 ◽

Cited By ~ 1

Author(s):

Vlade Vukadinovic ◽

Peter Habisreuther ◽

Nikolaos Zarzalis ◽

Rainer Suntz

Keyword(s):

Flame Front ◽

Burning Velocity ◽

Turbulent Flame ◽

Initial Pressure ◽

Front Propagation ◽

Mie Scattering ◽

Turbulent Flames ◽

Laser Method ◽

Turbulent Burning Velocity ◽

Optical Laser

In gas turbine operation a turbulent flame is employed. Thus, better understanding of the turbulent flame propagation is the key for further optimisation of turbine combustors and reduction of the environmental footprint. As turbulent flames are exposed to stretch, the effect of flame-stretch interaction must be better understood especially at higher pressures. In present study, turbulent burning velocity of two mixtures, hydrogen/air and propane/air, with negative and positive Ma, respectively are experimentally investigated in fan-stirred explosion vessel. For the investigation an optical laser method is employed based on the Mie-scattering of the laser light by smoke particles. Within this study the influence of initial parameters as initial pressure and turbulence intensity on the flame front propagation is investigated by giving special attention on influence of Ma variation. The experiments were performed at three different pressures 1, 2, 4 bar. The RMS fluctuation velocity was varied in the range of 0–2.77 m/s. The observed results are compared and discussed in detail.

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

Proceedings of the Institution of Mechanical Engineers Part D Journal of Automobile Engineering ◽

10.1243/0954407971526245 ◽

1997 ◽

Vol 211 (1) ◽

pp. 83-86 ◽

Cited By ~ 6

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.

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A spectral closure for premixed turbulent combustion in the flamelet regime

Journal of Fluid Mechanics ◽

10.1017/s0022112092002519 ◽

1992 ◽

Vol 242 ◽

pp. 611-629 ◽

Cited By ~ 120

Author(s):

N. Peters

Keyword(s):

Field Equation ◽

Scalar Field ◽

Dimensional Analysis ◽

Turbulent Combustion ◽

Burning Velocity ◽

Turbulent Flames ◽

Scalar Dissipation ◽

Premixed Turbulent Combustion ◽

Flame Stretch ◽

The Mean

Premixed turbulent combustion in the flamelet regime is analysed on the basis of a field equation. This equation describes the instantaneous flame contour as an isoscalar surface of the scalar field G(x,t). The field equation contains the laminar burning velocity sL as velocity scale and its extension includes the effect of flame stretch involving the Markstein length [Lscr ] as a characteristic lengthscale of the order of the flame thickness. The scalar G(x,t) plays a similar role for premixed flamelet combustion as the mixture fraction Z(x,t) in the theory of non-premixed flamelet combustion.Equations for the mean $\overline{G}$ and variance $\overline{G^{\prime 2}}$ are derived. Additional closure problems arise for the mean source terms in these equations. In order to understand the nature of these terms an ensemble of premixed flamelets with arbitrary initial conditions in constant-density homogeneous isotropic turbulence is considered. An equation for the two-point correlation $\overline{G^{\prime}({\boldmath x},t)G^{\prime}({\boldmath x}+{\boldmath r},t)}$ is derived. When this equation is transformed into spectral space, closure approximations based on the assumption of locality and on dimensional analysis are introduced. This leads to a linear equation for the scalar spectrum function Γ(k,t), which can be solved analytically. The solution Γ(k,t) is analysed by assuming a small-wavenumber cutoff at k0 = lT−1, where lT is the integral lengthscale of turbulence. There exists a $k^{-\frac{5}{3}}$ spectrum between lT and LG, where LG is the Gibson scale. At this scale turbulent fluctuations of the scalar field G(x,t) are kinematically restored by the smoothing effect of laminar flame propagation. A quantity called kinematic restoration ω is introduced, which plays a role similar to the scalar dissipation χ for diffusive scalars.By calculating the appropriate moments of Γ(k,t), an algebraic relation between ω, $\omega,\overline{G^{\prime}({\boldmath x},t)^2}$, the integral lengthscale lT and the viscous dissipation ε is derived. Furthermore, the scalar dissipation χ[Lscr ], based on the Markstein diffusivity [Dscr ][Lscr ] = sL [Lscr ], and the scalar-strain co-variance Σ[Lscr ] are related to ω. Dimensional analysis, again, leads to a closure of the main source term in the equation for the mean scalar $\overline{G}$. For the case of plane normal and oblique turbulent flames the turbulent burning velocity sT and the flame shape is calculated. In the absence of flame stretch the linear relation sT ∼ u′ is recovered. The flame brush thickness is of the order of the integral lengthscale. In the case of a V-shaped flame its increase with downstream position is calculated.

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A Model for Predicting Turbulent Burning Velocity by using Karlovitz Number and Markstein Number under EGR Conditions

10.4271/2021-01-1146 ◽

2021 ◽

Author(s):

Kei Yoshimura ◽

Kohei Ozawa ◽

Kyohei Yamaguchi ◽

Ratnak Sok ◽

Jin Kusaka ◽

...

Keyword(s):

Burning Velocity ◽

Markstein Number ◽

Turbulent Burning Velocity

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EXPERIMENTAL DETERMINATION OF LAMINAR BURNING VELOCITY OF BIOGAS AT PRESSURES UP TO 5 BAR

Revista de Engenharia Térmica ◽

10.5380/reterm.v17i2.64122 ◽

2018 ◽

Vol 17 (2) ◽

pp. 03

Author(s):

L. Pizzuti ◽

C. A. Martins ◽

L. R. Santos

Keyword(s):

Equivalence Ratio ◽

Burning Velocity ◽

Initial Pressure ◽

Experimental Setup ◽

Laminar Burning Velocity ◽

Gaseous Mixtures ◽

Experimental Procedure ◽

Constant Volume Combustion Chamber ◽

Percentage Standard Deviation

This paper presents a very detailed description of a new cylindrical constant volume combustion chamber designed for laminar burning velocity determination of gaseous mixtures at ambient temperature and initial pressure up to 6 bar. The experimental setup, the experimental procedure and the determination of the range of flame radius for laminar burning determination are all described in details. The laminar burning velocity of twelve synthetic biogas mixtures has been studied. Initial pressure varying between 1 and 5 bar, equivalence ratios, f, between 0.7 and 1.1 and percentage dilution, with a mixture of CO2 and N2, between 35 and 55% have been considered. Five experiments were run for each mixture providing a maximum percentage standard deviation of 8.11%. However, for two third of the mixtures this value is lower than 3.55%. A comparison with simulation using PREMIX for both GRI-Mech 3.0 and San Diego mechanisms has provided closer agreement for mixtures with equivalence ratio closer to stoichiometry whereas for f = 0.7 the deviation is larger than 15% for all pressures. Mixtures with lower equivalence ratio, higher dilution percentage and higher initial pressure presents the lower values of laminar burning velocity.

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