Asymptotic analysis of stationary adiabatic premixed flames in porous inert media

Pereira, Fernando M.; Oliveira, Amir Antônio Martins; Fachini, Fernando F.

doi:10.1016/j.combustflame.2008.08.003

Cited by 40 publications

(32 citation statements)

References 42 publications

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“…Then, since θ ( * )(0) sf = 1 as a first approximation, the parameter N ε , called the porous media flame number, is the parameter that defines universally the leading-order problem at the flame. This result has also been obtained in Pereira et al (2009).…”

Section: Outer Zone: Problem Of the Order Of Unitysupporting

confidence: 75%

“…Although the present model does not describe either the limit N ε → 0 or the limit N ε → ∞, the analysis of these limits is able to reveal qualitatively the results from Pereira et al (2009) The expression relating the flame velocity with the problem parameters is (3.41) in which δ = 1 + α θ ( * ) gf − 1 2 /β. In (3.41) the parameter n is a displacement in the coordinate axis in order to match the solution in the reaction length scale l R with the solution in the gas-phase diffusion length scale l G .…”

Section: Outer Zone: Problem Of the Order Of Unitymentioning

confidence: 80%

“…The analysis that justifies θ ( * )(0) s ∼ 1 is presented in Pereira et al (2009). In that work it is shown that as N → ∞ the solid-phase temperature at the flame θ sf tends to unity, and that θ sf is bounded by 1/2 < θ sf < 1.…”

Section: Outer Zone: Problem Of the Order Of Unitymentioning

confidence: 93%

“…A one-dimensional two-medium model for the conservation of mass, mass of chemical species, gas-phase energy and solid-phase energy is constructed, following Pereira et al (2009). The mass conservation implies that ρ n u n is constant for the one-dimensional flow with u n being the gas velocity far upstream from the flame.…”

Section: Mathematical Formulationmentioning

confidence: 99%

“…In a previous work (Pereira, Oliveira & Fachini 2009), an asymptotic solution was proposed for stationary adiabatic premixed flames in porous inert media taking advantage of the large difference between the thermal conductivity of the solid and gas phases. In that analysis, a two-equation model for the energy conservation is used with effective properties and a diffusion approximation for the intramedium radiation.…”

Section: Introductionmentioning

confidence: 99%

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Theoretical analysis of ultra-lean premixed flames in porous inert media

2010

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The structure of stationary adiabatic premixed flames within porous inert media under intense interphase heat transfer is investigated using the asymptotic expansion method. For the pore sizes of interest for combustion in porous inert media, this condition is reached for extremely lean mixtures where lower flame velocities are found. The flame structure is analysed in three distinct regions. In the outer region (the solid-phase diffusion length scale), both phases are in local thermal equilibrium and the problem formulation is reduced to the one-equation model for the energy conservation. In the first inner region (the gas-phase diffusion length scale), there is local thermal non-equilibrium and two equations for the energy conservation are required. In this region, the gas-phase temperature at the flame is limited by the interphase heat transfer. In the second inner region (the reaction length scale), the chemical reaction occurs in a very thin zone where the highest gas-phase temperature is found. The results showed that superadiabatic effects are reduced for leaner mixtures, smaller pore sizes and smaller fuel Lewis numbers. The results also show that there is a minimum superadiabatic temperature for the flame propagation to be possible, which corresponds to the lean flammability limit for the premixed combustion in porous inert media. A parameter that universalizes the leading-order flame properties is identified and discussed.

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Section: Outer Zone: Problem Of the Order Of Unitysupporting

confidence: 75%

Section: Outer Zone: Problem Of the Order Of Unitymentioning

confidence: 80%

Section: Outer Zone: Problem Of the Order Of Unitymentioning

confidence: 93%

Section: Mathematical Formulationmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Theoretical analysis of ultra-lean premixed flames in porous inert media

2010

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What is the leanest stream to sustain a nonadiabatic loop reactor: Analysis and methane combustion experiments

2016

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While previous studies experimentally demonstrated that loop reactor (LR) can be sustained with a lean feed (using ethylene combustion) and have analyzed the single‐reaction adiabatic case, this work analyzes the effects of heat loss and of reactor size to determine the leanest stream (expressed in terms of adiabatic temperature rise ΔTlim) that will sustain the operation. For an adiabatic infinitely long reactor ΔTlim→0 while for a finite reactor ΔTlim scales as (1 + Pe/4)−1 where Pe = Luρcpf/k, and heat loss increases this limit by (β/Pe)1/2. Thus, a good design of a LR will aim to decrease conductivity (k) and radial heat‐transfer coefficient (β) while increasing throughput (u) and reactor length. This article is also the first experimental demonstration of auto‐thermal operation in a LR for catalytic abatement of low‐concentration of methane, showing the leanest stream to be of 8000 ppm vs. 33,000 ppm in a once‐through reactor. Experimental combustion results of methane and of ethylene are compared with model predictions. © 2016 American Institute of Chemical Engineers AIChE J, 63: 2030–2042, 2017

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