The catalytic partial oxidation (CPO) of CH
4/O
2 mixtures diluted with large amounts of H
2O and CO
2 (up to 43 % and 21 % vol., respectively) was investigated experimentally and numerically in the pressure range 4 bar
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p ![]()
10 bar. Experiments were carried out in an optically accessible channel-flow catalytic reactor coated with Rh/ZrO
2, and included planar laser induced fluorescence (LIF) of formaldehyde for the assessment of homogeneous (gas-phase) ignition and one-dimensional spontaneous Raman measurements of all major gas-phase species for the evaluation of the heterogeneous (catalytic) processes. Simulations were performed with a full elliptic model that included detailed heterogeneous and homogeneous chemical reaction schemes. Over the reactor length with negligible gas-phase chemistry contribution, the employed heterogeneous reaction scheme provided good agreement to the measured methane consumption and synthesis gas yields, overpredicting mildly the partial over the total oxidation route. It was shown that the added water provided a source of O(s) and OH(s) surface radicals that enhanced the methane conversion and H
2 yields and reduced the CO yields. Moreover, the addition of CO
2 had a negligible chemical effect on the aforementioned parameters. An increase in pressure from 4 to 10 bar had a minor impact on the methane conversion and hydrogen selectivity. The employed gaseous scheme reproduced the LIF-measured onset of homogeneous ignition, although it underpredicted the extent of the formaldehyde zone ahead of the flame and the flame propagation characteristics at the highest investigated pressure (10 bar).
