Pressure dependent mechanism for H/O/C(1) chemistry

A pressure dependent kinetic sub-mechanism for H_xO_xC₁ species is developed based on literature data for reactions of the hydrogen-oxygen subset and paths involving abstraction of hydrogen atoms. Pressure and temperature dependent rate constants are determined for bimolecular, chemical activation (association and addition) and unimolecular (thermal) dissociation reactions using multi-frequency QRRK analysis for k(E) and master Equation analysis for fall-off. Pressure and temperature dependent rate constants are expressed in the form of 7×3 Chebyshev polynomials over 0.01 to 100 atm and 300 to 3000K. The chemical activation systems include reactions of OH, HO₂, O^•, O₂ with the following carbon species: CO, HC^•=O, CH₂=O, C^• H₂OH, CH₃O, CH₃ plus selected C₂ species, with dissociation analysis for stabilized adducts. Improved rate constants are used for HO₂ + CO reaction (near pressure independent) expressed as k_1a= 8.45 x10⁸xT^1.21 exp(17267cal/RT) and k_1b=7.14×10⁷xT^1.57 exp(17721cal/RT) cm³ mol^-1 s^-1 (two alternative channels leading to the same CO₂+OH products via different transition states) at CBS-QB3 level calculations and QRRK/ME analysis. Chemkin model results are compared with ignition time (delay) experiments in the CO/H₂/O_x system versus fuel equivalence ratio and pressure. The mechanism consists of ∼35 species and 150 reactions, with over 40 being pressure dependent.