Ignition, Liftoff, and Extinction of Gaseous Diffusion Flames

Liñán, A.; Vera, Marcos; Sánchez, Antonio L.

doi:10.1146/annurev-fluid-010814-014711

Cited by 56 publications

(36 citation statements)

References 84 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…The large variations in critical values of Fr observed in figure 3 would be considerably reduced should the characteristic scales of the flame, rather than those associated with fuel injection, be used in defining the relevant Froude number (Liñán et al 2015). Thus, with Re 1 and S 1 the flame length is of order SRea.…”

Section: Transition Diagramsmentioning

confidence: 93%

Diffusion-flame flickering as a hydrodynamic global mode

et al. 2016

View full text Add to dashboard Cite

The present study employs a linear global stability analysis to investigate buoyancyinduced flickering of axisymmetric laminar jet diffusion flames as a hydrodynamic global mode. The instability-driving interactions of the buoyancy force with the density differences induced by the chemical heat release are described in the infinitely fast reaction limit for unity Lewis numbers of the reactants. The analysis determines the critical conditions at the onset of the linear global instability as well as the Strouhal number of the associated oscillations in terms of the governing parameters of the problem. Marginal instability boundaries are delineated in the Froude-number/Reynolds-number plane for different fuel-jet dilutions. The results of the global stability analysis are compared with direct numerical simulations of time-dependent axisymmetric jet flames and also with results of a local spatio-temporal stability analysis.

show abstract

Section: Transition Diagramsmentioning

confidence: 93%

Diffusion-flame flickering as a hydrodynamic global mode

et al. 2016

View full text Add to dashboard Cite

show abstract

“…Understanding these interactions is crucial for determining the operability regime as well as the emissions from the burner. In the past, a number of studies [1][2][3][4] have been devoted to the characterization of these physics. In addition, both computational [5][6][7][8][9] and experimental [10][11][12] studies have been performed to identify the flame stabilization mechanism and analyze the sensitivity of the lift-off height to jet velocity and coflow temperature.…”

Section: Introductionmentioning

confidence: 99%

LES/PDF modeling of autoignition in a lifted turbulent flame: Analysis of flame sensitivity to differential diffusion and scalar mixing time-scale

Han

Raman

Chen

2016

Combustion and Flame

View full text Add to dashboard Cite

The stabilization of lifted flames involves a complex competition between small-scale mixing and propagation of flame kernels at the base of the flame. Here, the effect of species diffusivity on this stabilization process is explored. For this purpose, a large-eddy simulation (LES)/probability density function (PDF) methodology accounting for differential diffusion is developed. A dynamic model for scalar mixing time-scale is formulated to accurately describe the turbulence-driven mixing of scalars at the small-scales. Autoignition-stabilized H 2 /N 2 lifted turbulent flames in a vitiated coflow burner are chosen as test cases. Detailed chemical kinetics is used along with in situ adaptive tabulation (ISAT) to accelerate the computations. Four configuration test cases are considered: neglecting differential diffusion (Cases 1 and 2), considering differential diffusion (Case 3) and considering differential diffusion but neglecting molecular transport of H and H 2 (Case 4). A dynamic model for scalar mixing time-scale appearing in the mixing model is used in Cases 2, 3 and 4, which removes the need to specify the value of model constant. It is found that the lifted flames are very sensitive to differential diffusion. The predictions of major species mass fractions, temperatures and lift-off heights are in good agreement with the experimental data. Further, such agreement could be achieved without changing any boundary conditions. In particular, increased diffusion of species upstream allows ignition kernels to survive turbulent dissipation, causing stabilization to occur upstream. H 2 and H are identified as two critical species that play a dominant role in the differential diffusion effect. The model is also able to capture the change in lift-off height with change in coflow temperature. The results show that even in turbulent flames, stabilization of the flame zone can be sensitive to molecular diffusion. In LES computations where a significant part of this diffusion effect is resolved, the use of the enhanced LES/PDF/ISAT approach is seen as a promising approach for capturing the lift-off physics accurately.2 for in the solution to the one-dimensional flamelet equations. On the other hand, the spatial transport of this flame structure is through a conserved scalar (mixture fraction) and a reactive scalar representation. These scalars are necessarily transported using a single diffusivity. Consequently, the effect of differential diffusion at scales larger than the flame scales are neglected (or at best, inaccurately modeled). Blanquart et al. [31] have sought to address this issue by constructing mixture fraction equations that contain source terms to account for the change in species balance arising from differential diffusion. However, application of this approach to detailed chemistry based models is still being pursued. In the context of PDF methods, differential diffusion manifests in two different ways again. At the resolved scales, the PDF is altered by molecular diffusion through a second-order diffusion...

show abstract

“…Extinction criteria using Damköhler number (Williams, 1985), have been very important to define flammability maps, like the work of Lecoustre et al (Lecoustre, et al, 2010), that takes into account different extinction limits associated to aerodynamic, thermal and dilution quenching. On the other side, Liñán et al use the Damköhler number as a parameter to determine the structure and stability of diffusion jet flames (Liñán, et al, 2015), also on the basis of the previous work of Williams (Williams, 1971).…”

Section: Introductionmentioning

confidence: 99%

“…Flames burning vertically are symmetrical with respect to the fuel, while in the horizontal configuration it is necessary a forced flow to cancel the effect of natural convection, the latter being on the order of 30 cm/s for flames long about 2-3 cm (Liñán, et al, 2015).…”

Section: Introductionmentioning

confidence: 99%

Comparison of flame spread and blow-off extinction over vertical and horizontal PMMA samples

Carmignani

Lotti

Bhattacharjee

2016

Mechanical Engineering Journal

View full text Add to dashboard Cite

Flame spread in the kinetic regime and eventual extinction have been studied for more than four decades for the implications on fire safety and flame instabilities. It is well known that the ratio between the residence time and the combustion time at the leading edge, the so called Damköhler number, plays a fundamental role in the blowoff extinction of a spreading flame. However, the role of the boundary layer, which may significantly affect the residence time at the flame leading edge, on the blow-off extinction has not been thoroughly studied. In this work we present new experimental data on blow-off extinction of PMMA (polymethyl methacrylate) fuels and establish an empirical relation between the boundary layer development length and the extinction flow velocity. Using a vertical wind tunnel it has been possible to carry on a large number of experiments over thin PMMA samples, for an opposed flow velocity range from 0 cm/s up to 100 cm/s. Furthermore, it was possible to rotate the wind tunnel to obtain results with a horizontal configuration, reducing the effect of buoyancy on the flame spread. The experimental data reveal that the extinction length, the distance from the sample leading edge at which the blow-off extinction occurs, is directly related to the opposing flow velocity. Using a simplified scale analysis previously proved to be reliable, the blow-off extinction appeared to occur at a constant effective velocity (defined inside of the boundary layer). This conclusion can have important implications in the definition of the kinetic regime and the quantification of an extinction limit for thin fuels.

show abstract

Ignition, Liftoff, and Extinction of Gaseous Diffusion Flames

Cited by 56 publications

References 84 publications

Diffusion-flame flickering as a hydrodynamic global mode

Diffusion-flame flickering as a hydrodynamic global mode

LES/PDF modeling of autoignition in a lifted turbulent flame: Analysis of flame sensitivity to differential diffusion and scalar mixing time-scale

Comparison of flame spread and blow-off extinction over vertical and horizontal PMMA samples

Contact Info

Product

Resources

About