Flame stretch rate as a determinant of turbulent burning velocity

Abstract

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.

Explosion flame acceleration over obstacles: Effects of separation distance for a range of scales

“…Further examinations on flame extinction were conducted by Bradley et al [31]. The authors showed that KaLe > 1.5 corresponded to the lower boundary of the quenching process and a new quench limit was established to be KaLe ≥ 6 [31]. This therefore shows that turbulent flame quenching would not take place in multi-obstacle explosions unless the turbulence levels were high enough to achieve close to detonation conditions.…”

“…Abdel-Gayed et al [30] presented another correlation of flame quenching for Ka ≥ 1. Further examinations on flame extinction were conducted by Bradley et al [31]. The authors showed that KaLe > 1.5 corresponded to the lower boundary of the quenching process and a new quench limit was established to be KaLe ≥ 6 [31].…”

“…In the present work with turbulent to laminar burning velocity ratios up to 120, no total flame quench was observed. Figure 8 shows a plot of turbulent to laminar burning velocity ratios as a function of u'/SL and compared with the correlation of Bradley et al [31]. Also included in Fig.…”

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

“…Early generalisations of measured values of u t /u l were expressed first in terms of the product of Karlovitz and Lewis number of the deficient reactant, KLe [3], then later, KMa sr [6,13]. Latterly, it has proved necessary to separate K and Ma sr [17][18][19].…”

“…Asymptotic analysis attributed the changes to thermo-diffusive effects and possible flame extinctions at high flame stretch rates. The influence of the latter also featured in quantifications of a probability of burning, P b [2,3].…”