Lewis number effects on turbulent burning velocity

Abdel-Gayed, R.G.; Bradley, D.; Hamid, Mohd Norhakem; Lawes, M.

doi:10.1016/s0082-0784(85)80539-7

Cited by 156 publications

(85 citation statements)

References 16 publications

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“…18 It is worth noting here that alternative methods of assigning a characteristic Lewis number have been proposed based on heat release measurements 30,31 and mole fractions of the mixture constituents. 32 In the past, the significant effects of characteristic Lewis number Le on various aspects of premixed combustion (e.g., thermo-diffusive instability of laminar flames, burning rate, scalar gradient statistics, and combustion modelling) have been addressed analytically, [33][34][35][36] experimentally, [37][38][39][40][41][42][43] and numerically. 18,[44][45][46][47][48][49][50][51][52][53] Various concepts, which have been developed in order to explain such effects in turbulent flames, are reviewed elsewhere.…”

Section: Introductionmentioning

confidence: 99%

Effects of Lewis number on vorticity and enstrophy transport in turbulent premixed flames

2016

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The effects of Lewis number Le on both vorticity and enstrophy transport within the flame brush have been analysed using direct numerical simulation data of freely propagating statistically planar turbulent premixed flames, representing the thin reaction zone regime of premixed turbulent combustion. In the simulations, Le was ranged from 0.34 to 1.2 by keeping the laminar flame speed, thermal thickness, Damköhler, Karlovitz, and Reynolds numbers unchanged. The enstrophy has been shown to decay significantly from the unburned to the burned gas side of the flame brush in the Le ≈ 1.0 flames. However, a considerable amount of enstrophy generation within the flame brush has been observed for the Le = 0.34 case and a similar qualitative behaviour has been observed in a much smaller extent for the Le = 0.6 case. The vorticity components have been shown to exhibit anisotropic behaviour within the flame brush, and the extent of anisotropy increases with decreasing Le. The baroclinic torque term has been shown to be principally responsible for this anisotropic behaviour. The vortex stretching and viscous dissipation terms have been found to be the leading order contributors to the enstrophy transport for all cases, but the baroclinic torque and the sink term due to dilatation play increasingly important role for flames with decreasing Le. Furthermore, the correlation between the fluctuations of enstrophy and dilatation rate has been shown to play an important role in determining the material derivative of enstrophy based on the mean flow in the case of a low Le.

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Section: Introductionmentioning

confidence: 99%

Effects of Lewis number on vorticity and enstrophy transport in turbulent premixed flames

2016

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“…In contrast, Lewis numbers smaller than unity (deficient reactant mass transfer greater than heat transfer) are susceptible to intensify instabilities, as the flame speed increases for stronger stretched regions and the velocities at the crests of flame wrinkles should be higher than at the cusps. More details on the calculation of the Lewis number and its effect on laminar and turbulent flame speeds can be found in [73][74][75][76][77][78]. For calculating the Lewis number of the single component fuels used in this study (ethanol, butanol and isooctane) and at the engine's thermodynamic conditions at ignition timing, values of specific heats, thermal conductivity, density and viscosity of the mixtures, as well as diffusion coefficients, were required.…”

Section: Flame Front Crest and Cusp Velocitiesmentioning

confidence: 99%

“…These were taken from [79][80][81]; gasoline was exempted from this exercise due to lack of all necessary thermophysical properties. The binary diffusion coefficient for Le was based on either oxygen or the fuel as deficient reactants to produce 'lean' and 'rich' values, while the equivalent 'stoichiometric' value was based on the average of these two values following the methodology adopted by Bradley and co-workers [73][74][75][76].…”

Section: Flame Front Crest and Cusp Velocitiesmentioning

confidence: 99%

Flame front analysis of ethanol, butanol, iso-octane and gasoline in a spark-ignition engine using laser tomography and integral length scale measurements

Aleiferis

Behringer

2015

Combustion and Flame

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“…The importance of thermo-diffusive influences was shown experimentally through the influence of Lewis number at increasing Karlovitz stretch factor on the normalised turbulent burning velocity by Abdel-Gayed et al [1]. Asymptotic analysis attributed the changes to thermo-diffusive effects and possible flame extinctions at high flame stretch rates.…”

Section: Introductionmentioning

confidence: 97%

“…The overall mass rate of turbulent burning was expressed by the product of a mean surface area, a, of the appropriate turbulent flame front, the turbulent burning velocity, u t , and the density, u  , of the initial mixture. This was equated to the volumetric mass rate of burning at the wrinkled flame surface, with  integrated over the entire volume, V, of the reacting flame brush, giving: (1) Here, I o is a factor that allows for the influence of the stretch rate in changing the effective laminar burning velocity. Bray [5] derived an expression for the dependency of I o upon the laminar Karlovitz stretch factor and Markstein number.…”

Section: Introductionmentioning

confidence: 99%

Stretch rate effects and flame surface densities in premixed turbulent combustion up to 1.25 MPa

Bagdanavičius

Bowen

Bradley

et al. 2015

Combustion and Flame

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Key wordsTurbulent premixed flame, burning velocity, flame stretch rate, flame surface density, Markstein number. AbstractIndependent research at two centres using a burner and an explosion bomb has revealed important aspects of turbulent premixed flame structure. Measurements at pressures and temperatures up to 1.25 MPa and 673 K in the two rigs were aimed at quantifying the influences of flame stretch rate and strain rate Markstein number, Ma sr , on both turbulent burning velocity and flame surface density. That on burning velocity is expressed through the stretch rate factor, I o , or probability of burning, P b 0.5 . These depend on Ma sr , but they grow in importance as the Karlovitz stretch factor, K, increases, and are evaluated from the associated burning velocity data. Planar laser tomography was employed to identify contours of reaction progress variable in both rigs. These enabled both an appropriate flame front for the measurement of the turbulent burning velocity to be identified, and flame surface densities, with the associated factors, to be evaluated. In the explosion measurements, these parameters were derived also from the flame surface area, the derived P b 0.5 factor and the measured turbulent burning velocities. In the burner measurement they were calculated directly from the flame surface density, which was derived from the flame contours.A new overall correlation is derived for the P b 0.5 factor, in terms of Ma sr at different K and this is discussed in the light of previous theoretical studies. The wrinkled flame surface area normalised by the area associated with the turbulent burning velocity measurement, and the ratio of turbulent to laminar burning velocity, u t /u l , are also evaluated. The higher the value of , the more effective is an increased flame wrinkling in increasing u t /u l . A correlation of the product of k and the laminar flame thickness with Karlovitz stretch factor and Markstein number is explored using the present data and those of other workers. Some generality is revealed, enabling the wave length associated with the spatial change in mean reaction progress variable to be expressed by the number of laminar flame thicknesses, and the flame volume to be found.

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Lewis number effects on turbulent burning velocity

Cited by 156 publications

References 16 publications

Effects of Lewis number on vorticity and enstrophy transport in turbulent premixed flames

Effects of Lewis number on vorticity and enstrophy transport in turbulent premixed flames

Flame front analysis of ethanol, butanol, iso-octane and gasoline in a spark-ignition engine using laser tomography and integral length scale measurements

Stretch rate effects and flame surface densities in premixed turbulent combustion up to 1.25 MPa

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