Dynamics of premixed hydrogen/air flames in mesoscale channels

Pizza, Gianmarco; Frouzakis, Christos E.; Mantzaras, John; Tomboulides, Ananias; Boulouchos, Konstantinos

doi:10.1016/j.combustflame.2008.08.006

Cited by 112 publications

(56 citation statements)

References 28 publications

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“…The connective branches between the bifurcation point and the non-symmetric solutions are unstable and are not plotted in the figures. Hysteresis showing a double solution has already been reported in the dynamics of hydrogen-air flames in micro-and meso-scale channels with a prescribed wall temperature [17,18]. The inset in Figure 4(b) shows the same effect, that is, hysteresis in the symmetric solution branch.…”

Section: Symmetry-breaking Bifurcation Forsupporting

confidence: 59%

“…For example, for Le F < 1 we choose a lean hydrogen-air mixture at equivalence ratio φ = 0.5, such as done in [17][18][19]. For Le F = 1 a lean methaneair mixture at φ = 0.6 is selected.…”

Section: Scale Of the Problem And Thermodynamic Propertiesmentioning

confidence: 99%

“…Therefore, before extending the one-step model results to a detailed chemistry, as done in [17][18][19] for premixed hydrogen-air flames, or to a global reaction, as in [28][29][30] for methane-air flames, the present work addresses the influence of the preferential diffusion of the intermediate species on the flame dynamics by using a simple two-step chainbranching model. This chain-branching kinetics is usually preferred as a better approach to real hydrocarbons and hydrogen flame description than that of the simple one-step model [31][32][33].…”

Section: Introductionmentioning

confidence: 99%

“…When the channel height increases, a more complex dynamic arises: two oscillatory modes, symmetric and non-symmetric, can coexist; see [9]. Different burning modes such as mild combustion, ignition-extinction, steady symmetric and non-symmetric flames, and oscillating or pulsating flames, including cellular and chaotic behaviour, have been identified in the numerical simulation of premixed hydrogen-air flames in micro and meso channels with a specified wall temperature and using detailed chemistry and transport [17,18]. A complex combustion mode, called a spinning flame, where the flame presents a non-symmetric shape and rotates in the azimuthal direction, has also been reported recently in three-dimensional studies of hydrogen-air flames in tubes [19].…”

Section: Introductionmentioning

confidence: 99%

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The differential diffusion effect of the intermediate species on the stability of premixed flames propagating in microchannels

Fernández-Galisteo

Jiménez

Sánchez–Sanz

et al. 2014

Combustion Theory and Modelling

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The propagation of premixed flames in adiabatic and non-catalytic planar microchannels subject to an assisted or opposed Poiseuille flow is considered. The diffusive-thermal model and the well-known two-step chain-branching kinetics are used in order to investigate the role of the differential diffusion of the intermediate species on the spatial and temporal flame stability. This numerical study successfully compares steady-state and time-dependent computations to the linear stability analysis of the problem. Results show that for fuel Lewis numbers less than unity, Le F < 1, and at sufficiently large values of the opposed Poiseuille flow rate, symmetry-breaking bifurcation arises. It is seen that small values of the radical Lewis number, Le Z , stabilise the flame to symmetric shape solutions, but result in earlier flashback. For very lean flames, the effect of the radical on the flame stabilisation becomes less important due to the small radical concentration typically found in the reaction zone. Cellular flame structures were also identified in this regime. For Le F > 1, flames propagating in adiabatic channels suffer from oscillatory instabilities. The Poiseuille flow stabilises the flame and the effect of Le Z is opposite to that found for Le F < 1. Small values of Le Z further destabilise the flame to oscillating or pulsating instabilities.

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Section: Symmetry-breaking Bifurcation Forsupporting

confidence: 59%

Section: Scale Of the Problem And Thermodynamic Propertiesmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

The differential diffusion effect of the intermediate species on the stability of premixed flames propagating in microchannels

Fernández-Galisteo

Jiménez

Sánchez–Sanz

et al. 2014

Combustion Theory and Modelling

View full text Add to dashboard Cite

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“…The "FREI" phenomenon was also experimentally found and studied by Stazio et al [53] for a methane/air premixed flame in a 2.15-mm inner diameter straight tube with a prescribed wall temperature profile maintained by an external heating source, Richecoeur et al [54] for a non-premixed methane/oxygen flame in a 4-mm inner diameter curved duct without external heating, and Evans et al [55] for rich methane and propane/oxygen flames in 4-mm inner diameter non-externally-heated ducts made of different materials of quartz, glass and steel. Apart from experimental studies, the "FREI" was also successfully reproduced in numerical simulations [56][57][58][59][60][61][62].…”

Section: Fundamental Studiesmentioning

confidence: 87%

Micro/mesoscale combustion based portable power generating system

Kang¹

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Micro/mesoscale combustion-driven power generation is a promising alternative to replace traditional batteries for powering small scale electronics owing to its much higher energy densities. However, the considerable heat losses from the combustor walls due to the dramatically increased surface-tovolume ratio, as well as the short flow residence time at small scales pose a technical challenge in stabilising the flame inside the micro/mesoscale combustor. On the other hand, the significantly enhanced flame-wall thermal coupling at small scales can also lead to some unique flame characteristics.Recently, solid state power conversion of the heat released in the micro/mesoscale combustor such as thermoelectric (TE) and thermophotovoltaic (TPV) has been favoured over traditional power conversion methods such as micro-turbines. This is due to the excessive mechanical and viscous losses that rotating machinery suffers from upon miniaturisation.One of the main aims of this thesis is to perform numerical simulations to investigate the fundamental aspects of micro/mesoscale combustion, such as micro-flame behaviours of propagation and stabilisation, the conditions under which flame dynamics occur and the choices that suppress them. A set of modelling techniques that gives guidelines and practices for performing the time-accurate micro/mesoscale combustion simulations has been developed through investigation. Knowledge on standard and well-accepted numerical methods in literature are collected in a cohesive document. The less well-established modelling choices have been thoroughly evaluated and discussed.Using the developed numerical models, the effects of hydrogen and carbon monoxide addition on premixed methane/air flame dynamics is investigated. Results show that the flame instabilities which exist in pure methane/air flames could be effectively suppressed via a small amount of additives. Deep understanding of the underlying physics and chemistry has been gained. The effects of wall temperature profiles on the simulated micro-flame behaviours are also studied. The role of the combustion heat release and the gas-solid heat transfer in determining the micro-flame propagation speed is identified.Experimental works are also carried out, towards a full system demonstration for micro-power generation. The focus is placed on the "wall thermal engineering" on the improvement of the combustor performance and power output. The thermally-orthotropic pyrolytic graphite for the combustor wall material is explored. Compared to an isotropic material of stainless steel, a widened flame stability limit with pyrolytic graphite is demonstrated. Moreover, a uniform and moderate temperature distribution over the combustor surface is achieved, which is favourable for thermoelectric power conversion applications. Meanwhile, a novel, compact mesoscale thermophotovoltaic power generating system using a combination of porous media combustion and a simple band-pass filtering method is developed. The use of the porous media effectively enh...

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New Directions in Advanced Modeling and in Situ Measurements Near Reacting Surfaces

Mantzaras

2013

Flow Turbulence Combust

Self Cite

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Multidimensional numerical modeling and in situ spatially-resolved measurements of gas-phase thermoscalars over the catalyst boundary layer have fostered fundamental investigation of the heterogeneous and homogeneous chemical reaction pathways and their coupling at realistic operating conditions. The methodology for validating catalytic and gas-phase reaction mechanisms is firstly outlined for industrially-relevant fuels. Combination of advanced modeling and in situ near-wall species and velocity measurements is then used to address the intricate interplay between interphase fluid transport (laminar or turbulent) and hetero-/homogeneous kinetics. Controlling parameters of this interplay are the homogeneous ignition chemistry, flame propagation characteristics, competition between the catalytic and gaseous pathways for fuel consumption, diffusional imbalance of the limiting reactant, flow laminarization due to heat transfer from the hot catalytic walls, and fuel leakage through the gaseous reaction zone. Dynamic reactor operation and intrinsic flame dynamics driven by interactions between homogeneous kinetics and catalytic walls are outlined using detailed transient simulation. It is shown that the presence of catalytic reactions moderates flame instabilities. Future directions for transient modeling and for temporally-resolved in situ near-wall measurements are finally summarized. Keywords Hetero-/homogeneous combustion modeling • Near-wall in situ Raman • LIF and PIV measurements • Homogeneous ignition over catalytic surfaces • Turbulent channel flow catalytic combustion • Flame dynamics in catalytic channels Nomenclature B ratio of catalytically active to geometrical surface area c p , c s Specific heat of gas at constant pressure, specific heat of solid

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Dynamics of premixed hydrogen/air flames in mesoscale channels

Cited by 112 publications

References 28 publications

The differential diffusion effect of the intermediate species on the stability of premixed flames propagating in microchannels

The differential diffusion effect of the intermediate species on the stability of premixed flames propagating in microchannels

Micro/mesoscale combustion based portable power generating system

New Directions in Advanced Modeling and in Situ Measurements Near Reacting Surfaces

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