Effects of Lewis number on generation of primary acoustic instability in downward-propagating flames

Yoon, Sung Hwan; Noh, Tae Joon; Fujita, Osamu

doi:10.1016/j.proci.2016.09.013

Cited by 15 publications

(12 citation statements)

References 17 publications

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“…However, this regime was only observed in lean flames, because rich flames have relatively low Le (Φ = 0.8; Le ≈ 1.86 and Φ = 1.2; Le ≈ 1.04) and these are very sensitive to acoustic fluctuations even with very small SL [12]. When SL was low in rich flames, a regime of acoustic instability (Regime II) was identified in which the flame fronts were still curved, however, non-constant acoustic vibration showed up with small acoustic sound.…”

Section: Resultsmentioning

confidence: 99%

“…To solve this problem, we utilized the sustained thermoacoustic field, as a state of nature for a premixed flame propagating in an open-ended tube [8][9][10][11][12]. Since the acoustic field formed by the interaction between heat released by the flame and acoustic fluctuations suppresses the hydrodynamic instability, it enables observation of the pure pulsating instability.…”

Section: Introductionmentioning

confidence: 99%

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Experimental observation of pulsating instability under acoustic field in downward-propagating flames at large Lewis number

Yoon

Fujita

2018

Combustion and Flame

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According to previous theory, pulsating propagation in a premixed flame only appears when the reduced Lewis number, β(Le-1), is larger than a critical value (Sivashinsky criterion: 4(1+√3) ≈ 11), where β represents the Zel'dovich number (for general premixed flames, β ≈ 10), which requires Lewis number Le > 2.1. However, few experimental observation have been reported because the critical reduced Lewis number for the onset of pulsating instability is beyond what can be reached in experiments. Furthermore, the coupling with the unavoidable hydrodynamic instability limits the observation of pure pulsating instabilities in flames. Here, we describe a novel method to observe the pulsating instability. We utilize a thermoacoustic field caused by interaction between heat release and acoustic pressure fluctuations of the downward-propagating premixed flames in a tube to enhance conductive heat loss at the tube wall and radiative heat loss at the open end of the tube due to extended flame residence time by diminished flame surface area, i.e. flat flame. The thermoacoustic field allowed pure observation of the pulsating motion since the primary acoustic force suppressed the intrinsic hydrodynamic instability resulting from thermal expansion. By employing this method, we have provided new experimental observations of the pulsating instability for premixed flames. The Lewis number (i.e., Le ≈ 1.86) was less than the critical value suggested previously.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Experimental observation of pulsating instability under acoustic field in downward-propagating flames at large Lewis number

Yoon

Fujita

2018

Combustion and Flame

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“…However, when studying the stability of gas combustion, the perturbation of the flame front (instantaneous combustion front) is taken into account in any statement of the problem [1,3,29,30,32,33]. It is proved experimentally [34][35][36] that combustion acoustic perturbations generated by the flame affect the development of combustion instability.…”

Section: Discussion Of the Results Of The Study Of Combustion Stabilimentioning

confidence: 99%

“…After simple transformations, the boundary conditions (35) and (33) can be represented as Conditions (33) and (34), respectively, can be transformed to…”

Section: Fig 1 Stationary Solid Fuel Combustion Complexmentioning

confidence: 99%

A theoretical study of stability of solid fuel burning with a twophase gasification area

Волков

Makoyed

Loboda

et al. 2020

EEJET

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Theoretically, the combustion stability of solid fuel, which during the combustion process is decomposed according to the "solid phase-liquid phase-gas" scheme, is investigated. The physical and mathematical models for the propagation of small perturbations of combustion are constructed. The medium in all areas of combustion and in combustion products is assumed to be incompressible, and the viscosity of the fuel in the liquid phase is taken into account. Thus, perturbations of hydrodynamic parameters are considered not only in the two-phase gasification zone, but also in the combustion products area and the geometric perturbation of the instantaneous combustion front (flame), distorting the shape of its surface, is also specified. That is the characteristic feature of the presented physical model. The mathematical eigenvalue problem is set and solved. This problem is reduced to an algebraic characteristic equation for a dimensionless complex eigenvalue, which positivity determines the instability. It is proved that in the limiting case of the absence of a liquid phase, absolute instability takes place. At the other limiting case-for perturbations with infinite wavelength-a transition to stability takes place. The latter fact indicates that the presence of a viscous liquid film and changes in the length of the gasification zone under the influence of perturbations have a significant stabilizing effect on solid fuel combustion. In the general case, a sufficient condition for the instability of the roots of the characteristic equation is analytically determined. The physical interpretation of the mathematical results explains the processes of autoturbulization of solid fuel combustion and the possible transition of combustion to deflagration explosion or detonation. The results of the study are in qualitative agreement with experimental data and can additionally be used for theoretical analysis of the stability of the liquid fuel combustion process in the combustion chamber

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“…The Lewis number has generally been found to affect the behavior of flames in many ways. Its impacts on heat and mass transfer 2 , vorticity [3][4][5] and enstrophy 5 , scalar and surface density transport 6,7 , flame bifurcation and extinction 8 , stretched flame speeds 9 and generation of primary acoustic instability 10 have been reported, with numerical simulations particularly focusing on lean-premixed flames 11,12 .…”

Section: Introductionmentioning

confidence: 99%

Impacts of fuel nonequidiffusivity on premixed flame propagation in channels with open ends

et al. 2021

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The present study scrutinizes premixed flame dynamics in micro-channels, thereby shedding the light on advanced miniature micro-combustion technologies. While equidiffusive burning (when the Lewis number = 1) is a conventional approach adopted in numerous theoretical studies, real premixed flames are typically non-equidiffusive ( ≠ 1), which leads to intriguing effects, such as the diffusional-thermal instability. The equidiffusive computational study [Akkerman et al., Combust. Flame 145 (2006) 675] reported regular oscillations of premixed flames spreading in channels having nonslip walls and open extremes. Here, this investigation is extended to nonequidiffusive combustion in order to systematically study the impact of the Lewis number on the flame in this geometry. The analysis is performed by means of computational simulations of the reacting flow equations with fully-compressible hydrodynamics and one-step Arrhenius chemical kinetics in channels with adiabatic and isothermal walls. In the adiabatic channels, which are the main case of study, it is found that the flames oscillate at low Lewis numbers, with the oscillation frequency decreasing with ; while for the > 1 flames, a tendency to steady flame propagation is observed. The oscillation parameters also depend on the thermal expansion ratio and the channel width, though the impacts are rather quantitative than qualitative. The analysis is subsequently extended to the isothermal channels. It is shown that the role of heat losses to the walls is important and may potentially dominate over that of the Lewis number. At the same time, the impact of on burning in the isothermal channels is qualitatively weaker than that in the adiabatic channels.

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Effects of Lewis number on generation of primary acoustic instability in downward-propagating flames

Cited by 15 publications

References 17 publications

Experimental observation of pulsating instability under acoustic field in downward-propagating flames at large Lewis number

Experimental observation of pulsating instability under acoustic field in downward-propagating flames at large Lewis number

A theoretical study of stability of solid fuel burning with a twophase gasification area

Impacts of fuel nonequidiffusivity on premixed flame propagation in channels with open ends

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Effects of Lewis number on generation of primary acoustic instability in downward-propagating flames

Cited by 15 publications

References 17 publications

Experimental observation of pulsating instability under acoustic field in downward-propagating flames at large Lewis number

Experimental observation of pulsating instability under acoustic field in downward-propagating flames at large Lewis number

A theoretical study of stability of solid fuel burning with a two­phase gasification area

Impacts of fuel nonequidiffusivity on premixed flame propagation in channels with open ends

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A theoretical study of stability of solid fuel burning with a twophase gasification area