Experimental

Four different C1/H/O gas-phase mechanisms were investigated, which included the part of C2 chemistry that led to recombination of C1 radicals to C2 species. The mechanisms are further denoted as Warnatz-Maas, Warnatz et.al. and Leeds. The species transport properties were calculated from the Chemkin database. Each of the mechanisms in Refs. [22,35,36] was provided with its own thermodynamic data had the same thermo data as Warnatz. It is emphasized, however, that the discrepancies in the predictions with the above schemes (see next section) predominantly reflected kinetic and not thermodynamic differences; this was verified by interchanging the thermodynamic databases of the different mechanisms. Gas-phase and surface reaction rates were evaluated using Chemkin and Surface-Chemkin respectively. A set of

hetero/homogeneous schemes will be further denoted by the assigned names of its components, for example, Deutschmann/Warnatz schemes. Finally, the prefixes S and R will denote a surface and a gaseous reaction, respectively.

Conclusions

The homogeneous ignition of fuel-lean ( 0.31 £ j £ 0.40) methane/air mixtures over platinum was investigated in the pressure range 1 bar £ p £ 16 bar, which encompasses all practical catalytic combustion systems. In situ nonintrusive measurements of major species and trace species concentrations over the catalyst boundary layer of a channel-flow reactor were compared against detailed numerical predictions with elementary hetero/homogeneous chemical reaction schemes. The following are the key conclusions of this study. It was also shown that crucial in the performance of the gaseous schemes was the correct prediction of the minimum equivalence ratio above which the self-inhibited ignition behavior of methane was maintained. Finally, notwithstanding the ultra fuel-lean conditions, C2 chemistry could not be ignored. In particular, the inclusion of the radical recombination reaction CH₃+CH₃=C₂H₆was necessary for accurate homogeneous ignition predictions.

Lesson 14

Part 1

<== попередня сторінка	\|	наступна сторінка ==>
Gas phase chemistry in catalytic combustion of methane/air	\|	The rusting of metals

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