Laminar flamelet concepts in turbulent combustion

Peters, N.

doi:10.1016/s0082-0784(88)80355-2

Cited by 985 publications

(469 citation statements)

References 74 publications

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“…Such flames have been observed experimentally [2,3], as shown in Fig. 1, and, as transient laminar flamelets, they probably play a role in the combustion of turbulent diffusion flames, where extinction, diffusive mixing, and subsequent reignition of pockets of gas may occur [4]. To date there has been little theoretical work which models this type of flame structure.…”

Section: Introductionmentioning

confidence: 81%

Flame propagation in a nonuniform mixture: Analysis of a slowly varying Triple Flame

Dold

1989

Combustion and Flame

254

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For flames propagating through a nonuniform medium a three-flame structure is described. This consists of a fuelrich premixed flame, a fuel-lean premixed flame, and, starting where these flames meet, a diffusion flame. Such formations have been observed experimentally and probably occur as laminar flamelets in turbulent diffusion flames. A low-heat-release model for such flame structures is developed and solutions are obtained in the limit of slowly varying premixed flames. Under these conditions, it is shown that the Triple-Flame propagation speed depends on the transverse mixture fraction gradient and is bounded above by the maximum adiabatic laminar flame speed of the system.

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Section: Introductionmentioning

confidence: 81%

Flame propagation in a nonuniform mixture: Analysis of a slowly varying Triple Flame

Dold

1989

Combustion and Flame

254

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“…Extinction is associated with small decrements of the temperature in the reaction layer from the peak value Tf, which when of order F?/T a are sufficient to reduce the reaction rate by a factor e, as can be inferred from the exponential temperature dependence in (2). The ratio of the characteristic temperature increase by the chemical reaction, given by q/(S+ 1), to this Frank-Kamenetskii temperature, Tf/T a , defines the Zel'dovich number of order T a \Tf for large S, as the relevant large parameter in the asymptotic description.…”

Section: Finite-rate Effects For Large Activation Energymentioning

confidence: 99%

“…Of paramount importance are his contributions to reduced-kinetic mechanisms, and to the development of flamelet-modeling approaches for the description of finite-rate effects in turbulent combustion [1]. In his famous 1984 review paper [2], he explained in an exemplarily pedagogic manner the role of laminar diffusion flamelets in turbulent non-premixed combustion, building on ideas introduced earlier by Forman Williams [3]. As stated by Norbert Peters [2], "the steady laminar counterflow diffusion flame exhibits a very similar scalar structure as unsteady distorted mixing layers in a turbulent flow field", which leads him to propose the counterflow geometry as "the most representative steady flow field to study chemistry models and molecular transport effects in laminar flamelets".…”

Section: Introductionmentioning

confidence: 99%

“…In his famous 1984 review paper [2], he explained in an exemplarily pedagogic manner the role of laminar diffusion flamelets in turbulent non-premixed combustion, building on ideas introduced earlier by Forman Williams [3]. As stated by Norbert Peters [2], "the steady laminar counterflow diffusion flame exhibits a very similar scalar structure as unsteady distorted mixing layers in a turbulent flow field", which leads him to propose the counterflow geometry as "the most representative steady flow field to study chemistry models and molecular transport effects in laminar flamelets". In the present paper, we pay homage to Norber Peters by revisiting the counterflow diffusion flame, with particular attention given to differential-diffusion effects on flame extinction.…”

Section: Introductionmentioning

confidence: 99%

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The large-activation-energy analysis of extinction of counterflow diffusion flames with non-unity Lewis numbers of the fuel

Liñán¹,

Martínez-Ruiz

Vera

et al. 2017

Combustion and Flame

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Large-activation-energy asymptotic techniques are used to describe the effects of non-unity Lewis numbers of the fuel on strain-induced extinction of axisymmetric counterflow diffusion flames. The present work extends and clarifies previous investigations by accounting also for variable density and variable transport properties of the gas. In our asymptotic analysis the flame structure near extinction is, at leading order, given by the Burke-Schumann limit of infinitely fast reaction; i.e. two outer regions of equilibrium flow, with the fuel and the oxygen separated by an infinitesimally thin reaction layer where they arrive by diffusion in stoichiometric proportions. The leading-order description provides the basic flow structure, including the flame-sheet location, the fuel-consumption rate, the temperature gradients on both sides of the flame, and the peak value of the temperature, which plays a dominant role in flame extinction and differs significantly from the adiabatic-flame value for non-unity Lewis numbers. In the near-extinction regime small departures, due to finite rates, from the fast-reaction limit are enough to dominate the structure of the reaction layer, and must be taken into account in this thin layer and in the outer chemically frozen regions, where the corrections are associated with the reactants leaking, with small mass fractions, through the flame. The main effect of the differential diffusion in the nearextinction regime is due to the strong modification of the reaction rates resulting from the changes in the Burke-Schumann peak temperature, with only moderate corrections due to leakage of the reactants through the flame. For large values of the overall stoichiometric ratio S of the diffusion flame, defined as the mass of the air stream needed to burn to completion the unit mass of the fuel stream, the extinction conditions occur in a premixed-flame regime, in which the reaction layer is displaced towards the fuel side with respect to the Burke-Schumann flame sheet position and a fraction of the arriving fuel mass flux leaks through the reaction layer, while the mass fraction of the leaking oxygen decreases to negligibly small values. The asymptotic predictions are tested by comparison with numerical integrations of extinction curves based on continuation methods.

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“…Different physical processes may dominate these interactions at different regions of the relevant parameter space [42,57,58]. We can define four different flame regimes [59]: 'wrinkled flamelets', 'corrugated flamelets', 'well-stirred reactor', 'distributed reaction zone'. Flame regimes described as wrinkled or corrugated flamelets correspond to situations where the reactions occur in thin sheets that retain their laminar structure.…”

Section: Combustion Modelsmentioning

confidence: 99%