Two-dimensional modelling for catalytically stabilized combustion of a lean methane-air mixture with elementary homogeneous and heterogeneous chemical reactions

Dogwiler, Urs; Benz, P.; Mantzaras, John

doi:10.1016/s0010-2180(98)00036-4

Cited by 113 publications

(70 citation statements)

References 21 publications

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“…Gas phase species adsorption rates are described in terms of sticking coefficient; the probability that a collision of the particular species k with the surface will result in adsorption. The adsorption rate constant kad,k of k-th gaseous species is modeled using a modified Motz-Wise correction (Dogwiler et al, 1999):…”

Section: Chemical Kineticsmentioning

confidence: 99%

CFD Modeling of the Combustion Characteristics and Stability in Catalytic Micro-Channels

Junjie¹,

Xu²

2017

AJHMT

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Combustion characteristics and stability of premixed methane-air mixtures in catalytic micro-channels is studied numerically, using CFD (computational fluid dynamics). The characteristics of the fluid mechanics are also analyzed. A two-dimensional CFD model with detailed reaction mechanisms and multicomponent transport is developed to evaluate the effect of operating conditions on the combustion stability. The laminar flow is assumed, and steady-steady simulations are performed. The fuel-lean equivalence ratio operation limit for the system is determined by the analysis of Reynolds number. The primary focus is on CFD as a means of understanding thermal management at small scales. It is shown that an appropriate choice of the flow velocity is crucial in achieving the self-sustained operation. Large gradients in temperature and species concentration are observed, despite the small scales of the system under certain conditions. The flow velocity is very important as it determines the flame location. Furthermore, the flow velocity plays a dual, competing role in the stability of the system. Low flow velocities reduce the heat generation, whereas high flow velocities reduce the convective time-scale. There is a narrow regime of flow velocities that allows self-sustained operation. When a low-power system is desired, highly insulating materials should be preferred, whereas a high-power system would favor highly conductive materials. Engineering maps that delineate combustion stability are constructed. In order to gain further insight into the combustion characteristics of the system, the optimum Reynolds number is determined. Finally, design recommendations are made.

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Section: Chemical Kineticsmentioning

confidence: 99%

CFD Modeling of the Combustion Characteristics and Stability in Catalytic Micro-Channels

Junjie¹,

Xu²

2017

AJHMT

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“…In particular oxidation reactions over noble metals have been modeled extensively such as of hydrogen [38][39][40][41][42][43][44] , CO [45][46][47] , and methane [31,[48][49][50][51][52] and ethane [22,26,53,54] over Pt, formation of synthesis gas over Rh [52,55] . Lately, mechanisms have been established for more complex reaction systems, for instance, three-way catalysts [56] or Chemical Vapor Deposition (CVD) reactors for the formation of diamond [57,58] , silica [59] , and nanotubes [60] .…”

Section: B Development Of Multi-step Surface Reaction Mechanismsmentioning

confidence: 99%

“…For instance, an optically accessible catalytic channel reactor can be used to evaluate models for heterogeneous and homogeneous chemistry as well as transport by the simultaneous detection of stable species by Raman measurements and OH radicals by Planar laser-induced fluorescence (PLIF) [68,69] . Exemplarily, Figure 3 comparison of the experimentally derived ignition distances with numerical elliptic twodimensional simulations of the flow field using combinations of a variety of schemes [70][71][72][73] .…”

Section: Model Evaluationmentioning

confidence: 99%

Computational Fluid Dynamics Simulation of Catalytic Reactors

Deutschmann

2008

Handbook of Heterogeneous Catalysis

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Catalytic reactors are generally characterized by the complex interaction of various physical and chemical processes. Monolithic reactors can serve as example, in which partial oxidation and reforming of hydrocarbons, combustion of natural gas, and the reduction of pollutant emissions from automobiles are frequently carried out. Figure 1 illustrates the physics and chemistry in a catalytic combustion monolith that glows at a temperature of about 1300 K due to the exothermic oxidation reactions. In each channel of the monolith, the transport of momentum, energy, and chemical species occurs not only in flow (axial) direction, but also in radial direction. The reactants diffuse to the inner channel wall, which is coated with the catalytic material, where the gaseous species adsorb and react on the surface. The products and intermediates desorb and diffuse back into the bulk flow. Due to the high temperatures, the chemical species may also react homogeneously in the gas phase. In catalytic reactors, the catalyst material is often dispersed in porous structures like washcoats or pellets. Mass transport in the fluid phase and chemical reactions are then superimposed by diffusion of the species to the active catalytic centers in the pores. The temperature distribution depends on the interaction of heat convection and conduction in the fluid, heat release due to chemical reactions, heat transport in the solid material, and thermal radiation. If the feed conditions vary in time and space and/or heat transfer occurs between the reactor and the ambience, a non-uniform temperature distribution over the entire monolith will result, and the behavior will differ from channel to channel.Today, the challenge in catalysis is not only the development of new catalysts to synthesize a desired product, but also the understanding of the interaction of the catalyst with the surrounding reactive flow field. Sometimes, the exploitation of these interactions can lead to

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“…The governing equations were discretized with a finite volume scheme and the solution was obtained iteratively using a SIMPLER (Patankar, 1980) method for the pressure-velocity field. Details on the solution algorithm have been provided elsewhere (Dogwiler et al, 1999;Mantzaras et al, 2000). An orthogonal staggered grid of 380 Â 120 points (in x and y, respectively) with finer x-spacing closer to the entrance and y-spacing closer to the walls was sufficient to produce a grid-independent solution.…”

Section: Numerical Two-dimensional Channel Modelmentioning

confidence: 99%

EFFECTS OF H₂O AND CO₂DILUTION ON THE CATALYTIC AND GAS-PHASE COMBUSTION OF METHANE OVER PLATINUM AT ELEVATED PRESSURES

Reinke

Mantzaras

Bombach

et al. 2007

Combustion Science and Technology

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The impact of large exhaust gas dilution (up to 59.5% H 2 O and 30.3% CO 2 per vol.) on the heterogeneous (catalytic) and homogeneous (gas-phase) steady combustion of fuel-lean CH 4 =O 2 =N 2 mixtures over platinum has been investigated experimentally and numerically at pressures of 5 to 14 bar. In situ, one-dimensional Raman measurements of major gas-phase species concentrations and planar laser induced fluorescence (LIF) of the OH radical were used to assess the heterogeneous and homogeneous combustion processes, respectively. Comparisons between measurements and and CO 2 dilution. The addition of water inhibits the catalytic reactivity due to the increase in the surface coverage of OH(s) that, in turn, reduces the available free platinum sites. This inhibition has been quantified in terms of operating pressure, temperature, and amount of water dilution through an appropriate one-step catalytic reaction for the complete oxidation of methane. Water promotes chemically the onset of homogeneous ignition, as it directly impacts the radical pool buildup. On the other hand, the chemical effect of CO 2 on either reaction pathway is negligible. The influence of H 2 O and CO 2 dilution to the coupling between the two reaction pathways is elucidated and implications for the application of catalytically stabilized combustion to new power generation cycles with large exhaust gas dilution are addressed.

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Two-dimensional modelling for catalytically stabilized combustion of a lean methane-air mixture with elementary homogeneous and heterogeneous chemical reactions

Cited by 113 publications

References 21 publications

CFD Modeling of the Combustion Characteristics and Stability in Catalytic Micro-Channels

CFD Modeling of the Combustion Characteristics and Stability in Catalytic Micro-Channels

Computational Fluid Dynamics Simulation of Catalytic Reactors

EFFECTS OF H₂O AND CO₂DILUTION ON THE CATALYTIC AND GAS-PHASE COMBUSTION OF METHANE OVER PLATINUM AT ELEVATED PRESSURES

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Two-dimensional modelling for catalytically stabilized combustion of a lean methane-air mixture with elementary homogeneous and heterogeneous chemical reactions

Cited by 113 publications

References 21 publications

CFD Modeling of the Combustion Characteristics and Stability in Catalytic Micro-Channels

CFD Modeling of the Combustion Characteristics and Stability in Catalytic Micro-Channels

Computational Fluid Dynamics Simulation of Catalytic Reactors

EFFECTS OF H2O AND CO2DILUTION ON THE CATALYTIC AND GAS-PHASE COMBUSTION OF METHANE OVER PLATINUM AT ELEVATED PRESSURES

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EFFECTS OF H₂O AND CO₂DILUTION ON THE CATALYTIC AND GAS-PHASE COMBUSTION OF METHANE OVER PLATINUM AT ELEVATED PRESSURES