Premixed flames subjected to extreme levels of turbulence part I: Flame structure and a new measured regime diagram

Skiba, A.; Wabel, Timothy M.; Carter, Campbell D.; Hammack, Stephen D.; Temme, Jacob; Driscoll, James F.

doi:10.1016/j.combustflame.2017.08.016

Cited by 129 publications

(66 citation statements)

References 78 publications

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“…Under leaner conditions, it is easier for the flames to become distributed. Skiba et al [13] measured the Bunsen-type flame structures in 16 cases with φ = 0.65 and 0.85. They found that the preheat zone is dramatically broadened at high Ka, especially at higher equivalence ratio.…”

Section: Introductionmentioning

confidence: 99%

Response of heat release to equivalence ratio variations in high Karlovitz premixed H2/air flames at 20 atm

Wang

Jin

Luo

2019

International Journal of Hydrogen Energy

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Reaction layer thickness Δx Grid resolution κ Mean curvature v Kinematic viscosity v'kj Forward stoichiometric coefficient for species k in reaction j v''kj Reverse stoichiometric coefficient for species k in reaction j φ Equivalence ratio of the fresh mixture φL Local equivalence ratio ω  Species reaction rate Ai Pre-exponential factor of Arrhenius equation c Progress variable Ei Activation energy of a reaction Ka Karlovitz number Kf Forward reaction rate constant Kr Reverse reaction rate constant K0 Limit of low-pressure reaction rate constant K∞ Limit of high-pressure reaction rate constant Kci Equilibrium constant t l Integral length scale [M] Overall contribution of different species in Three-body reactions Re Reynolds number SL Laminar flame speed Syz Cross-section area T Local temperature Tu Temperature of unburnt gas Tb Temperature of burnt gas ' u Root-mean-square turbulent velocity fluctuation Vrec Reaction zone volume Xk Molar concentration of species k , f k Y Local mass fraction of species k

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Section: Introductionmentioning

confidence: 99%

Response of heat release to equivalence ratio variations in high Karlovitz premixed H2/air flames at 20 atm

Wang

Jin

Luo

2019

International Journal of Hydrogen Energy

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“…Therefore, this work aims at filling this gap by comparing differently defined surface-averaged quantities and relevant evolution equations in order to show that the difference referred to is of fundamental importance. For instance, as will be argued later, such a difference should be taken into account when discussing an apparent physical paradox, i.e., contradiction between data [49,50,59] that indicate thinning of local reaction waves in turbulent flows and data [40,51,55,[60][61][62][63] that show the opposite effect. A detailed review of relevant experimental and DNS data can be found elsewhere [63,64].…”

Section: Introductionmentioning

confidence: 99%

Surface-averaged quantities in turbulent reacting flows and relevant evolution equations

Lipatnikov

2019

Phys. Rev. E

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While quantities conditioned to an isosurface of reaction progress variable c, which characterizes fluid state in a turbulent reacting flow, have been attracting rapidly growing interest in the recent literature, a mathematical and physical framework required for research into such quantities has not yet been elaborated properly. This paper aims at filling two fundamental gaps in this area, i.e., (i) ambiguities associated with a definition of a surface-averaged quantity and (ii) the lack of rigorous equations that describe evolutions of such quantities. In the first (theoretical) part of the paper, (a) analytical relations between differently defined (area-weighted and unweighted) surface-averaged quantities are obtained and differences between them (quantities) are discussed, (b) a unified method for deriving an evolution equation for bulk area-weighted surface-averaged value of a local characteristic φ of a turbulent reacting flow is developed, and (c) the method is applied for deriving evolution equations for the bulk area-weighted surface-averaged reaction-surface density |∇c|, local reactionwave thickness 1/|∇c|, and local displacement speed S d , i.e., the speed of an isosurface of the c(x, t) field with respect to the local flow. In the second (numerical) part of the paper, direct numerical simulation data obtained recently from a highly turbulent reaction wave are analyzed in order to (1) highlight substantial differences between area-weighted and unweighted surface-averaged quantities and (2) show that various terms in the derived evolution equations are amenable to accurate numerical evaluation in spite of appearance of the so-called zero-gradient points [C. H. Gibson, Phys. Fluids 11, 2305 (1968)] in a highly turbulent medium. Finally, the obtained analytical and numerical results are used to shed light on the paradox of local flame thinning and broadening which is widely discussed in the turbulent combustion literature.

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“…By increasing the diameter of pilot flame burner from 22 mm to 61 mm, the central jet flame can be stabilized at much higher jet velocity, e.g., at 330 m/s, without observing flame quenching. Driscoll and colleges (Skiba et al 2018(Skiba et al , 2016Wabel, Skiba, Driscoll 2017) conducted a series experiments on the Michigan Hi-Pilot (High Reynolds number-piloted flame) burner. They observed that a smaller pilot flame could not shield the flame from ambient air; the cold air entrainment could significantly affect the reaction layer downstream (Skiba et al 2016).…”

Section: Introductionmentioning

confidence: 99%

Numerical Studies of the Pilot Flame Effect on a Piloted Jet Flame

Shu

Bai

Zhou

et al. 2019

Combustion Science and Technology

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In a piloted jet flame, the pilot flame has an effect of stabilizing the main flame. Detailed mechanisms of pilot flame/main flame interaction are however not well studied. It is expected that the pilot flame affects the main flame through the following mechanisms: (a) the pilot flame provides the heat and radicals to the reaction zone of the main flame, (b) the pilot flame prevents the cold ambient air from being entrained into the main flame, and (c) the pilot flame modifies the stretch rate of the main flame. In this paper, detailed numerical simulations of piloted laminar methane/air jet flames are carried out to elucidate the effect of pilot flame on the structure and burning velocity of the main jet flame. One-dimensional (1D) freely propagating flame is also simulated to investigate the effect of hot gas mixing with the unburned fuel/air mixture, and 1D counter-flow flame is simulated to study the diffusion of the hot gas from the pilot flame to the reaction zone of the main flame and the effect of flame stretch. The results showed that heat transfer from the pilot flame to the main flame has a more significant effect on the structures and propagation of the main flame than the mass transfer from the pilot flame to the main flame. The heat and mass transfer from the pilot flame affects the local equivalence ratio and temperature of the unburned mixture, which gives rise to a significant enhancement of burning velocity. When the hot gas from the pilot flame is at sufficiently high temperatures, an ultra-lean fuel/air mixture can burn at equivalence ratio below the flammability limit. The reaction rate and burning velocity of ultra fuel-lean flames are enhanced by the strain rate, whereas for a main flame with the equivalence ratio closer to that of pilot flame, the reactivity and burning velocity of the main flame decrease with increasing strain rate.

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Premixed flames subjected to extreme levels of turbulence part I: Flame structure and a new measured regime diagram

Cited by 129 publications

References 78 publications

Response of heat release to equivalence ratio variations in high Karlovitz premixed H2/air flames at 20 atm

Response of heat release to equivalence ratio variations in high Karlovitz premixed H2/air flames at 20 atm

Surface-averaged quantities in turbulent reacting flows and relevant evolution equations

Numerical Studies of the Pilot Flame Effect on a Piloted Jet Flame

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