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Show research literature. Results were updated for the 279 reactions (49 species) in version 2.11. As in prior mechanisms, the pressure dependences of recombination and decomposition rate constants are appropriately parameterized, so wide ranges of temperature (1000-3500K) and pressure (0-20 bar) are accommodated. For GRI-Mech 3.0, propane chemistry was included in a form suitable for describing its role in natural gas combustion. This minimal set includes the reactions of propane and propyl radical only. Acetaldehyde and C H 2 C H O were added as products of C 2 species oxidation. Among the changes based on n ew elementary rate data are revised expressions for H + 0 2 (+M) reactions producing H 0 2 , new results for the C H 3 + 0 2 reaction which is important to methane ignition, and high temperature data on several C H reactions. Acquiring improved rate constant results can help constrain the ranges available to the optimization, and the optimization and target sensitivity analysis themselves can suggest where improved basic kinetics measurements are most needed. A set of 82 experimental measurements was selected from the literature and our previous target and validation lists to represent combustion properties that the mechanism is optimized to predict. These targets include flame velocities, shock tube ignition delays, and species profiles in shock tubes, flow reactors and low pressure flames. N e w targets focusing on formaldehyde oxidation and the C H intermediate in prompt N O formation and reburn were added for the version 3.0 optimization. Shock tube targets on propane-assisted ignition delays of methane were included also. The nitrogen target list was reevaluated and expanded since its first inclusion in the optimization (version 2.11), although the general shortage and lack of overlap of this set remains a problem. Significant revisions have been made on some targets as well, in light of new experimental data showing that methane flame speeds are lower than the 1.2 target values (due to stretch effects), and based on new, more precise measurements of higher prompt N O amounts produced in low pressure flames. These experiments were modeled using the trial mechanism of evaluated rate parameters, with the Chemkin-II set of codes,[4] including sensitivity analysis. For those targets such as ignition delays where direct sensitivity output was not available, repeated computations using 2k and k/2 for each rate constant were made to compute a brute force sensitivity coefficient. Some typical results are shown in the bar graphs of Figure 1 for the experimental targets described in the caption. H+02=0+OH H+CHj(*M) = CH4(+M) OH+CO = H+C02 H+02+H20 = H02+H20 OH+CH3 = CHj(S)+H20 H02+CH3=OH+CH30 HCOHjO = H+CO*H20 H*CH4 = CH,*H2 OH*H02=02«-H20 H+OH+M = H20+M H+CjH4(+M) = CjH^+M) H+02+Nj=H02+N2 -0 - - > . jiB r i 2-0.1 0 0.1 0.2 0.3 0.4 0. CH* 02 = OHCO CH+NO = HCN+O CH+NO = N+HCO CH+NO = H+NCO CH*H2 = H+CHj CHj+NO = H+HNCO OCHj = H+H2+CO HCO+HJOH+CO+HJO H+CH = C+H2 CH+H20 = H+CH20 5 -0 04 -0.02 0 002 0.04 Figure 1. Sensitivity coefficients for some experimental targets: (left) A stoichiometric methane-air flame speed at 5 bar 400K; (right) The ratio of C H with and without 1.2% N O seeded into a stoichiometric 10 torr methane-oxygen-argon flame. 5 |