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Profile measurements of the H 2 /O 2 reaction have been obtained using a variable pressure flow reactor over pressure and temperature ranges of 0.3-15.7 atm and 850-1040 K, respectively. These data span the explosion limit behavior of the system and place significant emphasis on HO 2 and H 2 O 2 kinetics. The explosion limits of dilute H 2 /O 2 /N 2 mixtures extend to higher pressures and temperatures than those previously observed for undiluted H 2 /O 2 mixtures. In addition, the explosion limit data exhibit a marked transition to an extended second limit which runs parallel to the second limit criteria calculated by assuming HO 2 formation to be terminating. The experimental data and modeling results show that the extended second limit remains an important boundary in H 2 /O 2 kinetics. Near this limit, small increases in pressure can result in more than a two order of magnitude reduction in reaction rate. At conditions above the extended second limit, the reaction is characterized by an overall activation energy much higher than in the chain explosive regime.The overall data set, consisting primarily of experimentally measured profiles of H 2 , O 2 , H 2 O, and temperature, further expand the data base used for comprehensive mechanism development for the H 2 /O 2 and CO/H 2 O/O 2 systems. Several rate constants recommended in an earlier reaction mechanism have been modified using recently published rate constant data for H ϩ O 2 (ϩ N 2 ) ϭ HO 2 (ϩ N 2 ), HO 2 ϩ OH ϭ H 2 O ϩ O 2 , and HO 2 ϩ HO 2 ϭ H 2 O 2 ϩ O 2 . When these new rate constants are incorporated into the reaction mechanism, model predictions are in very good agreement with the experimental data.

Flow reactor experiments were performed to study moist CO oxidation in the presence of trace quantities of NO (0-400 ppm) and SO 2 (0-1300 ppm) at pressures and temperatures ranging from 0.5-10.0 atm and 950-1040 K, respectively. Reaction profile measurements of CO, CO 2 , O 2 , NO, NO 2 , SO 2 , and temperature were used to further develop and validate a detailed chemical kinetic reaction mechanism in a manner consistent with previous studies of the CO/H 2 /O 2 /NO X and CO/H 2 O/N 2 O systems. In particular, the experimental data indicate that the spin-forbidden dissociation-recombination reaction between SO 2 and Oatoms is in the fall-off regime at pressures above 1 atm. The inclusion of a pressure-dependent rate constant for this reaction, using a high-pressure limit determined from modeling the consumption of SO 2 in a N 2 O/SO 2 /N 2 mixture at 10.0 atm and 1000 K, brings model predictions into much better agreement with experimentally measured CO profiles over the entire pressure range. Kinetic coupling of NO X and SO X chemistry via the radical pool significantly reduces the ability of SO 2 to inhibit oxidative processes. Measurements of SO 2 indicate fractional conversions of SO 2 to SO 3 on the order of a few percent, in good agreement with previous measurements at atmospheric pressure. Modeling results suggest that, at low pressures, SO 3 formation occurs primarily through SO 2 ϩ O(ϩM) ϭ SO 3 (ϩM), but at higher pressures where the fractional conversion of NO to NO 2 increases, SO 3 formation via SO 2 ϩ NO 2 ϭ SO 3 ϩ NO becomes important. For the conditions explored in this study, the primary consumption pathways for SO 3 appear to be SO 3 ϩ HO 2 ϭ HOSO 2 ϩ O 2 and SO 3 ϩ H ϭ SO 2 ϩ OH. Further study of these reactions would increase the confidence with which model predictions of SO 3 can be viewed.

Flow reactor experiments were performed over wide ranges of pressure (0.5-14.0 atm) and temperature (750-1100 K) to study H 2 /O 2 and CO/H 2 O/O 2 kinetics in the presence of trace quantities of NO and NO 2 . The promoting and inhibiting effects of NO reported previously at near atmospheric pressures extend throughout the range of pressures explored in the present study. At conditions where the recombination reaction H ϩ O 2 (ϩM) ϭ HO 2 (ϩM) is favored over the competing branching reaction, low concentrations of NO promote H 2 and CO oxidation by converting HO 2 to OH. In high concentrations, NO can also inhibit oxidative processes by catalyzing the recombination of radicals. The experimental data show that the overall effects of NO addition on fuel consumption and conversion of NO to NO 2 depend strongly on pressure and stoichiometry. The addition of NO 2 was also found to promote H 2 and CO oxidation but only at conditions where the reacting mixture first promoted the conversion of NO 2 to NO.Experimentally measured profiles of H 2 , CO, CO 2 , NO, NO 2 , O 2 , H 2 O, and temperature were used to constrain the development of a detailed kinetic mechanism consistent with the previously studied H 2 /O 2 , CO/H 2 O/O 2 , H 2 /NO 2 , and CO/H 2 O/N 2 O systems. Model predictions generated using the reaction mechanism presented here are in good agreement with the experimental data over the entire range of conditions explored.