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

Abstract

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.

Modeling of the Interactions Between Catalytic Surfaces and Gas-Phase

“…Here, probability density functions (PDFs) [37], either derived from transport equations [48] or empirically constructed [49], are used to take the turbulent fluctuations into account when calculating the chemical source terms. For the simulation of reactions on catalysts it is also important to use appropriate models for the laminarization of the turbulent flow near the solid surface [47,50]. Multi-phase dispersed flows such as in fluidized beds are another class of flow systems in catalytic converters, which is still a very active field of research.…”

“…Mantzaras et al [116] applied the k-e model, a presumed (Gaussian) probability density function for gaseous reactions, and a laminar-like closure for surface reactions to study turbulent catalytically stabilized combustion of lean hydrogen-air mixtures in plane platinumcoated channels; a system very relevant for catalytic combustion stages in gas turbines, which reduces NO x emissions and increases efficiencies. They also examined different low-Reynolds number near-wall turbulence models and compared the numerically predicted results with data derived from planar laser-induced fluorescence measurements of OH radicals, Raman measurements of major species and laser doppler velocimetry measurements of local velocities and turbulence [50]. They found that discrepancies between predictions and measurements can be 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.…”

Computational Fluid Dynamics Simulation of Catalytic Reactors

“…Useful data arise from the experimental resolution of local velocity profiles by laser Doppler anemometry/velocimetry (LDA, LDV) [15,66,67] and of spatial and temporal species profiles by in situ, non-invasive methods such as Raman and laser induced fluorescence (LIF) spectroscopy. 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] .…”

“…They also examined different low-Reynolds number near-wall turbulence models and compared the numerically predicted results with data derived from planar laser-induced fluorescence measurements of OH radicals, Raman measurements of major species and laser doppler velocimetry measurements of local velocities and turbulence [68] . They found that discrepancies between predictions and measurements are 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.…”

04/02340 High-pressure experiments and modeling of methane/air catalytic combustion for power-generation applications

“…Nevertheless, recent studies on turbulent, CST combustion [5,6] have shown that under the strong flow laminarization induced by heat transfer from the hot catalyst surfaces, laminar modeling remains a very good approximation, even with incoming Reynolds numbers up to 6000.…”