Hetero-/homogeneous combustion of hydrogen/air mixtures over platinum at pressures up to 10 bar
01 Jan 2009-Vol. 32, Iss: 2, pp 1937-1945
TL;DR: In this paper, the authors investigated the heterogeneous combustion of fuel-lean hydrogen/air premixtures over platinum in an optically accessible channel-flow catalytic reactor and included planar laser induced fluorescence (LIF) of the OH radical for the assessment of homogeneous (gas-phase) ignition, and 1-D Raman measurements of major gas-phase species concentrations for the evaluation of the catalytic processes.
Abstract: The hetero-/homogeneous combustion of fuel-lean hydrogen/air premixtures over platinum was investigated experimentally and numerically in the pressure range 1 bar ⩽ p ⩽ 10 bar. Experiments were carried out in an optically accessible channel-flow catalytic reactor and included planar laser induced fluorescence (LIF) of the OH radical for the assessment of homogeneous (gas-phase) ignition, and 1-D Raman measurements of major gas-phase species concentrations for the evaluation of the heterogeneous (catalytic) processes. Simulations were performed with a full-elliptic 2-D model that included detailed heterogeneous and homogeneous chemical reaction schemes. The predictions reproduced the measured catalytic hydrogen consumption, the onset of homogeneous ignition at pressures of up to 3 bar and the diminishing gas-phase combustion at p ⩾ 4 bar. The suppression of gaseous combustion at elevated pressures bears the combined effects of the intrinsic homogeneous hydrogen kinetics and of the hetero/homogeneous chemistry coupling via the catalytically produced water over the gaseous induction zone. Transport effects, associated with the large diffusivity of hydrogen, have a smaller impact on the limiting pressure above which gaseous combustion is suppressed. It is shown that for practical reactor geometrical confinements, homogeneous combustion is still largely suppressed at p ⩾ 4 bar even for inlet and wall temperatures as high as 723 and 1250 K, respectively. The lack of appreciable gaseous combustion at elevated pressures is of concern for the reactor thermal management since homogeneous combustion moderates the superadiabatic surface temperatures attained during the heterogeneous combustion of hydrogen.
Citations
More filters
TL;DR: A review of microcombustion research can be found in this article, where the authors present technological drivers, applications, devices, and fabrication protocols of microburners, as well as a review of homogeneous, catalytic, homogeneous-heterogeneous and heat recirculating micro-burners.
324 citations
TL;DR: In this article, a brief explanation for the manufacturing of ceramic and metallic monoliths has been provided, and different methods for coating γ-alumina, as a secondary support, are included.
Abstract: Considerable research has been conducted on monolithic catalysts for various applications. Strategies toward coating monoliths are of equal interest and importance. In this paper, the preparation of monoliths and monolithic catalysts have been summarized. More specifically, a brief explanation for the manufacturing of ceramic and metallic monoliths has been provided. Also, different methods for coating γ-alumina, as a secondary support, are included. Techniques used to deposit metal-based species, zeolites and carbon onto monoliths are discussed. Furthermore, monoliths extruded with metal oxides, zeolites and carbon are described. The main foci are on the reasoning and understanding behind the preparation of monolithic catalysts. Ideas and concerns are also contributed to encourage better approaches when designing these catalysts. More importantly, the relevance of monolithic structures to reactions, such as the selective oxidation of alkanes, catalytic combustion for power generation and the preferential oxidation of carbon monoxide, has been described.
144 citations
TL;DR: In this paper, the authors investigated the catalytic combustion of syngas/air mixtures over Pt using 2D steady and transient computer codes with detailed hetero-/homogeneous chemistry, transport, and heat transfer mechanisms in the solid.
Abstract: The catalytic combustion of syngas/air mixtures over Pt has been investigated numerically in a channel-flow configuration using 2D steady and transient computer codes with detailed hetero-/homogeneous chemistry, transport, and heat transfer mechanisms in the solid. Simulations were carried out for syngas compositions with varying H2 and CO contents, pressures of 1 to 15 bar, and linear velocities relevant to power generation systems. It is shown that the homogeneous (gas-phase) chemistry of both H2 and CO cannot be neglected at elevated pressures, even at the very large geometrical confinements relevant to practical catalytic reactors. The diffusional imbalance of hydrogen can lead, depending on its content in the syngas, to superadiabatic surface temperatures that may endanger the catalyst and reactor integrity. On the other hand, the presence of gas-phase H2 combustion moderates the superadiabatic wall temperatures by shielding the catalyst from the hydrogen-rich channel core. Above a transition tempera...
93 citations
TL;DR: The gas-phase combustion of H2/O2/N2 mixtures over platinum was investigated experimentally and numerically at fuel-lean equivalence ratios up to 0.30, pressures up to 15 bar and preheats up to 790 K as discussed by the authors.
69 citations
TL;DR: In this article, the effects of pre-ignition energy releases on H 2 O 2 mixtures were explored in a shock tube with the aid of high-speed imaging and conventional pressure and emission diagnostics.
64 citations
References
More filters
01 Sep 1989
3,517 citations
"Hetero-/homogeneous combustion of h..." refers methods in this paper
...gas-phase and surface reaction rates were evaluated with CHEMKIN [21] and Surface-CHEMKIN [22], respectively....
[...]
...The gas-phase ignition delays were computed using CHEMKIN [25] at various constant temperatures in order to mimic the presence of the hot catalytic walls that heat the flowing reacting gas (the ignition delays were defined as the times required for hydrogen to drop to 50% of its initial concentration)....
[...]
...Mixture-average diffusion, including thermal diffusion for the light species H and H2, was used in conjunction with the CHEMKIN transport database [23]....
[...]
...This mechanism has been validated against shock tube and laminar flame speed measurements at pressures up to 87 bar. gas-phase and surface reaction rates were evaluated with CHEMKIN [21] and Surface-CHEMKIN [22], respectively....
[...]
01 Dec 1986
TL;DR: This report documents a Fortran computer code package that is used for the evaluation of gas-phase multicomponent viscosities, thermal conductivities, diffusion coefficients, and thermal diffusion coefficients.
Abstract: This report documents a Fortran computer code package that is used for the evaluation of gas-phase multicomponent viscosities, thermal conductivities, diffusion coefficients, and thermal diffusion coefficients. The package is in two parts. The first is a preprocessor that computes polynomial fits to the temperature dependent parts of the pure species viscosities and binary diffusion coefficients. The coefficients of these fits are passed to a library of subroutines via a linking file. Then, any subroutine from this library may be called to return either pure species properties or multicomponent gas mixture properties. This package uses the chemical kinetics package CHEMKIN, and transport property subroutines are designed to be used in conjunction with the CHEMKIN subroutine library. This package supersedes a previously-written transport property code package in which we used certain mixture averaging rules to compute mixture properties rather than the full multicomponent formulation.
1,262 citations
"Hetero-/homogeneous combustion of h..." refers methods in this paper
...Mixture-average diffusion, including thermal diffusion for the light species H and H2, was used in conjunction with the CHEMKIN transport database [23]....
[...]
TL;DR: A comprehensively tested H2/O2 chemical kinetic mechanism based on the work of Mueller et al. 1 and recently published kinetic and thermodynamic information is presented in this paper, which is validated against a wide range of experimental conditions, including those found in shock tubes, flow reactors, and laminar premixed flame.
Abstract: A comprehensively tested H2/O2 chemical kinetic mechanism based on the work of Mueller et al. 1 and recently published kinetic and thermodynamic information is presented. The revised mechanism is validated against a wide range of experimental conditions, including those found in shock tubes, flow reactors, and laminar premixed flame. Excellent agreement of the model predictions with the experimental observations demonstrates that the mechanism is comprehensive and has good predictive capabilities for different experimental systems, including new results published subsequent to the work of Mueller et al. 1, particularly high-pressure laminar flame speed and shock tube ignition results. The reaction H + OH + M is found to be primarily significant only to laminar flame speed propagation predictions at high pressure. All experimental hydrogen flame speed observations can be adequately fit using any of the several transport coefficient estimates presently available in the literature for the hydrogen/oxygen system simply by adjusting the rate parameters for this reaction within their present uncertainties. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36: 566–575, 2004
988 citations
TL;DR: In this article, nine different concepts for natural gas fired power plants with CO2 capture have been investigated, and a comparison is made based on net plant efficiency and emission of CO2, where a 400MW combined cycle plant is applied as a reference case.
346 citations
TL;DR: In this article, the authors measured the exit temperatures of methane/hydrogen/air mixtures flowing at atmospheric pressure through platinum coated honeycomb channels and investigated a single channel of this monolith by a two-dimensional Navier-Stokes simulation including an elementary-step surface reaction mechanism.
333 citations