Effect of Pressure on the Catalytic Reactivity

Comparisons between Raman-measured and predicted transverse profiles of CsHg and H2O mole fractions, at four selected streamwise locations, are illustrated in Fig. 4.1 for Cases 1 for clarity, 27 of the total 63 measured points are provided. Modest profile asymmetries are evident due to small differences between the upper- and lower-wall temperatures (see the wall temperatures of Fig. 4.2). 

Axial profiles of the computed catalytic (O and gas-phase (G) propane conversion rates (the latter integrated over the 7-mm channel height), are presented in Fig. 4.2 for Cases 1-4. 

The maximum reactor extent over which the G conversion is negligible has been delineated with the arrows in Fig. 4.2 (defined as the positions where the G conversion amounts to 5% of the C conversion). For the assessment of the catalytic reactivity, the forthcoming comparisons of Raman data with predictions are limited to this extent so as to avoid falsification of the catalytic kinetics by gas-phase chemistry. The initial reactor extent over which the gas-phase contribution could be safely neglected ranged from 10.9 cm (Case 3) to 14.2 cm (Case 4). 

The heterogeneous reactivity of propane was assessed by varying the reactor pressure and surface temperature, and monitoring the near-wall bending of the propane transverse profiles. In Case 2 (Fig. 4.1, p = 3 bar) the catalytic fuel conversion is already appreciable at surface temperatures 850 K, while mass-transport-limited conditions are approached for = 1064 K (manifested by the low propane mole fractions near both walls in Fig. 4.1 (2d)). 

In contrast, previous CHj/air studies [8] in the same reactor necessitated an increase in pressure to achieve a similar level of reactivity under the same mass 

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