Numerical modeling of catalytic ignition

Deutschmann, Olaf; Schmidt, Ralf; Behrendt, Frank; Warnat, J.

doi:10.1016/s0082-0784(96)80400-0

Cited by 323 publications

(215 citation statements)

References 17 publications

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“…The surface site density was 2.7 ‫ן‬ 10 ‫9מ‬ mol/cm 2 , simulating polycrystalline platinum [1,5]; the thick (2.2 lm) platinum layer on top of a non-porous Al 2 O 3 layer, closely resembled such a surface. For gaseous combustion, the H 2 /O 2 scheme of Warnatz et al [22] (38 reactions and nine species including N 2 ) was used.…”

Section: Chemical Kineticsmentioning

confidence: 99%

“…For surface chemistry, the H 2 /O 2 scheme over Pt by Deutschmann [1] was employed (five surface species, six gaseous species, and 16 reactions). The surface site density was 2.7 ‫ן‬ 10 ‫9מ‬ mol/cm 2 , simulating polycrystalline platinum [1,5]; the thick (2.2 lm) platinum layer on top of a non-porous Al 2 O 3 layer, closely resembled such a surface.…”

Section: Chemical Kineticsmentioning

confidence: 99%

“…The numerical models should be capable of reproducing crucial CST characteristics such as light-off, catalytic fuel conversion, and-for safety reasonsthe onset of homogeneous ignition. Elementary heterogeneous reaction schemes for simple fuels (CH 4 , CO, and H 2 ) over Pt were developed and tested in their capacity to reproduce measured light-off characteristics and minor species fluxes [1][2][3], whereas combined hetero-/homogeneous schemes for CH 4 and H 2 over Pt were validated recently [4,5]. In particular, the experimental and numerical investigation of Appel et al [5] assessed the homogeneous ignition capabilities of various H 2 /O 2 hetero-/homogeneous reaction schemes.…”

Section: Introductionmentioning

confidence: 99%

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An experimental and numerical investigation of turbulent catalytically stabilized channel flow combustion of hydrogen/air mixtures over platinum

Appel

Mantzaras

Schaeren

et al. 2002

Proceedings of the Combustion Institute

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The turbulent catalytically stabilized combustion (CST) of fuel-lean hydrogen/air mixtures over platinum was investigated experimentally and numerically in channel-flow configurations. Experiments were performed in an optically accessible catalytic channel reactor, established by two Pt-coated ceramic plates 300 mm long and placed 7 mm apart, with incoming Reynolds numbers of 15,000 and 30,000. Planar laserinduced fluorescence of the OH radical was used to monitor the onset of homogeneous (gas-phase) ignition, one-dimensional (across the 7 mm transverse direction) Raman measurements of major species and temperature assessed the turbulent scalar transport, laser doppler velocimetry yielded the inlet velocity and turbulence, and thermocouples embedded beneath the catalyst provided the surface temperature distribution. Computations were carried out with a two-dimensional elliptic fluid mechanical code that included elementary heterogeneous and homogeneous chemical reaction schemes. Three different low-Reynolds number near-wall turbulence models were examined, in conjunction with a thermochemistry model that included a presumed-shape (Gaussian) probability density function approach for the gaseous reactions and a laminar-like closure for catalytic reactions. Comparisons between predictions and measurements have shown that key CST issues, such as catalytic fuel conversion and onset of homogeneous ignition, are strongly dependent on the particular turbulence model. Moreover, the discrepancies between predictions and measurements were ascribed to the capacity of the various turbulence models to capture the strong flow laminarization induced by the heat transfer from the hot catalytic surfaces. A turbulence model that yields good agreement with the measurements is presented as particularly suited for CST. Experiments and predictions have shown that a continuous increase of the turbulent transport led to incomplete combustion through the gaseous reaction zone with subsequent catalytic conversion of the leaked fuel and, finally, to extinction of the gaseous flame.

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Section: Chemical Kineticsmentioning

confidence: 99%

Section: Chemical Kineticsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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An experimental and numerical investigation of turbulent catalytically stabilized channel flow combustion of hydrogen/air mixtures over platinum

Appel

Mantzaras

Schaeren

et al. 2002

Proceedings of the Combustion Institute

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“…It is also of practical importance, among other reasons because the catalytic removal of molecular hydrogen in nuclear plants may alleviate one of the main concerns in nuclear power safety. Typically, catalytic combustion processes have been studied either by numerical simulations using elementary chemistry [1][2][3][4][5][6][7][8][9] or by large activation energy asymptotic analyses using a one-step overall reaction mechanism [10][11][12][13][14]. Williams et al [1] proposed a model for the catalytic combustion of hydrogen at high temperatures.…”

Section: Introductionmentioning

confidence: 99%

“…Warnatz and coworkers [2,3] studied the catalytic combustion and ignition of hydrogen using detailed kinetic mechanisms for both surface and gas-phase reactions. Deutschmann et al [4] studied the catalytic ignition of different fuels on different catalyst materials. In their numerical simulations, they showed that one or the other reactant almost covers the surface before ignition.…”

Section: Introductionmentioning

confidence: 99%

Transient ignition and combustion of diluted hydrogen/air mixtures by a thin catalytic wire

Treviño

Higuera²,

Liñán³

2002

Proceedings of the Combustion Institute

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This paper reports on a study of transient ignition and combustion of hydrogen/air mixtures by a heated, thin catalytic wire in a natural convection environment. Modeling of the process is accomplished via a reduced set of heterogeneous kinetic processes which include dissociative adsorption and desorption of both reactants, three fast surface reactions of the Langmiur-Hinshelwood type, and the desorption reaction of the adsorbed product, H 2 O(s). The overall surface reaction rate is found to be limited by the adsorption rate of molecular oxygen, which depends on the concentration of molecular oxygen close to the surface of the wire and the distribution of empty sites in the catalyst. The analysis allows the determination of the critical conditions for ignition and the ignition delay time as a function of the important physicochemical parameters. The resulting wire temperatures and the critical value of the external heating rate at ignition are computed. The analysis shows how the ignition temperature increases as the external heating rate increases. The configuration dependence of the ignition temperature is taken as an indication that the use of a critical Damkö hler number provides a better ignition condition than the ignition temperature concept. A self-sustained combustion regime for strong diluted mixtures is described.

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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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Numerical modeling of catalytic ignition

Cited by 323 publications

References 17 publications

An experimental and numerical investigation of turbulent catalytically stabilized channel flow combustion of hydrogen/air mixtures over platinum

An experimental and numerical investigation of turbulent catalytically stabilized channel flow combustion of hydrogen/air mixtures over platinum

Transient ignition and combustion of diluted hydrogen/air mixtures by a thin catalytic wire

Computational Fluid Dynamics Simulation of Catalytic Reactors

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