Catalytic combustion of hydrogen-air mixtures in stagnation flows

Ikeda, Hideto; Libby, Paula A.; Williams, Forman A.; Sato, Junichi

doi:10.1016/0010-2180(93)90088-k

Cited by 44 publications

(23 citation statements)

References 12 publications

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“…Stagnation point flows have provided a particularly amenable platform for such studies (see, e.g. [4][5][6]). The regimes of homogeneous hydrocarbon combustion were identified in Song et al [4] using bifurcation theory and one-step chemistry for both the gaseous and surface kinetics.…”

Section: Introductionmentioning

confidence: 99%

“…The regimes of homogeneous hydrocarbon combustion were identified in Song et al [4] using bifurcation theory and one-step chemistry for both the gaseous and surface kinetics. Ikeda et al [5] investigated the homogeneous ignition of hydrogen-air mixtures using detailed gaseous and simplified surface kinetics while Bui et al [6] employed detailed gaseous and surface reaction schemes. The two-dimensional external flow studies included boundary layer (parabolic) models for flows over flat catalytic plates with simplified surface and detailed gaseous chemistries and addressed primarily the effect of radical adsorption-desorption reactions on gaseous ignition [7][8][9][10].…”

Section: Introductionmentioning

confidence: 99%

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Numerical modelling of turbulent catalytically stabilized channel flow combustion

et al. 2000

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The turbulent catalytically stabilized combustion of lean hydrogen-air premixtures is investigated numerically in plane channels with platinum-coated isothermal walls. The catalytic wall temperature is 1220 K and the incoming mixture has a mean velocity of 15 m/s and a turbulent kinetic energy of 1.5 m 2 /s 2 . A two-dimensional elliptic model is developed with elementary heterogeneous and homogeneous chemical reactions. The approach is based on a two-layer k-ε model of turbulence, a Favre-average moment closure, a presumed-shape (Gaussian) probability density function for gaseous reactions, and a laminar-like closure for surface reactions. Gaseous combustion is confined close to the catalyst surface due to the diffusional imbalance of the limiting reactant (hydrogen). In addition, the peak rms temperature and species fluctuations are always located outside the extent of the homogeneous reaction zone indicating that thermochemical fluctuations have no significant influence on gaseous combustion. Turbulence is significantly suppressed by gaseous combustion resulting in higher turbulent transport for the leaner mixtures, a successive push of the gaseous reaction zone towards the wall, incomplete combustion, and subsequent catalytic conversion of the leaked fuel. Comparison between turbulent and laminar cases having the same incoming properties shows that turbulence inhibits homogeneous ignition due to increased heat transport away from the near-wall layer.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Numerical modelling of turbulent catalytically stabilized channel flow combustion

et al. 2000

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“…Such simulations include one-dimensional stagnation point flows [5,6], two-dimensional parabolic (boundary layer) flows [7,8], and two-dimensional elliptic channel flows [9,10]; all of these used detailed gas phase chemistry and, at least for the twodimensional cases, either a mass-transport limited global reaction or simplified surface kinetics. Fundamental questions addressed in the previous as well as other similar studies were ignition and extinction (blowout) characteristics of CST as a function of fuel type and equivalence ratio, wall temperature, inlet reactant velocity and temperature, and catalyst activity [6 -14]; identification of the regimes of catalytic combustion (heterogeneous vs homogeneous reactions and inhibition of one path over the other) [5]; Lewis number effects of diffusionally imbalanced mixtures on catalyst wall temperatures [10 -12]; and effect of catalytic fuel conversion on combustion efficiency and pollutant (NO x ) reduction [15,16]. Catalytic combustors, such as those used in natural gas fired turbines, are usually made of a catalytically active monolith-bed consisting of a multitude of tubular channels.…”

Section: Introductionmentioning

confidence: 99%

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

Dogwiler

Benz

Mantzaras

1999

Combustion and Flame

113

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The catalytically stabilized combustion (CST) of a lean (equivalence ratio ⌽ ϭ 0.4) methane-air mixture was investigated numerically in a laminar channel flow configuration established between two platinum-coated parallel plates 50 mm long and 2 mm apart. A two-dimensional elliptic fluid mechanical model was used, which included elementary reactions for both gaseous and surface chemistry. Heat conduction in the solid plates and radiative heat transfer from the hot catalytic surfaces were accounted for in the model. Heterogeneous ignition occurs just downstream of the channel entrance, at a streamwise distance ( x) of 4 mm. Sensitivity analysis shows that key surface reactions influencing heterogeneous ignition are the adsorption of CH 4 and O 2 and the recombinative desorption of surface-bound O radicals; the adsorption or desorption of radicals other than O has no effect on the heterogeneous ignition location and the concentrations of major species around it. Homogeneous ignition takes place at x ϭ 41 mm. Sensitivity analysis shows that key surface reactions controlling homogeneous ignition are the adsorption/desorption of the OH radical and the adsorption/ desorption of H 2 O, the latter due to its direct influence on the OH production path. In addition, the slope of the OH lateral wall gradient changes from negative (net-desorptive) to positive (net-adsorptive) well before homogeneous ignition ( x ϭ 30 mm), thus exemplifying the importance of a detailed surface chemistry scheme in accurately predicting the homogeneous ignition location. The effect of product formation on homogeneous ignition was studied by varying the third body efficiency of H 2 O. Product formation promotes homogeneous ignition due to a shift in the relative importance of the reactions H ϩ O 2 ϩ M 3 HO 2 ϩ M and HCO ϩ M 3 CO ϩ H ϩ M.

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“…The pre-exponential and activation energy are adjusted so that ignition happens at a positive power [24], and the catalytic ignition temperature is close to experiments for 0.8% hydrogen in air [25]. The rate expression can be found in the previous work of Ikeda et al [26], in which the interaction between heterogeneous and homogeneous reactions arising when a mixture of hydrogen and air impinges on a platinum plate at elevated temperature has been studied. The relevant kinetics parameters can be found in the previous work of Petersson and Ackelid [27] as well as Johansson et al [28].…”

Section: Effect Of Compositionmentioning

confidence: 88%

Catalytic Ignition and Extinction of Hydrogen-Air Mixtures on Platinum Surfaces with Detailed Kinetics and Transport

2016

European Reviews of Chemical Research

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Surface ignition and extinction of very fuel-lean hydrogen-air mixtures on platinum surfaces were modeled using a detailed surface kinetic mechanism and transport phenomena. A stagnationpoint flow geometry was employed to study the effect of heat flux, flow velocity, and composition on the surface ignition and extinction. The temperature and concentration on platinum surfaces as well as the coverage of surface species were also explored to evaluate the role of gas-phase chemistry. It was shown that the platinum surface can be poisoned by different adsorbates, and the dynamic process of surface ignition and extinction is associated with a phase transition from one poisoning species to another. For certain temperatures, multiple poisoned states of the surface coexist. Comparisons of simulations with experiments were carried out, and the results revealed that the self-inhibition of hydrogen surface ignition is caused by poisoning of platinum by atomic hydrogen.

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Catalytic combustion of hydrogen-air mixtures in stagnation flows

Cited by 44 publications

References 12 publications

Numerical modelling of turbulent catalytically stabilized channel flow combustion

Numerical modelling of turbulent catalytically stabilized channel flow combustion

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

Catalytic Ignition and Extinction of Hydrogen-Air Mixtures on Platinum Surfaces with Detailed Kinetics and Transport

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