New experimental profiles of stable species concentrations are reported for formaldehyde oxidation in a variable pressure flow reactor at initial temperatures of 850-950 K and at constant pressures ranging from 1.5 to 6.0 atm. These data, along with other data published in the literature and a previous comprehensive chemical kinetic model for methanol oxidation, are used to hierarchically develop an updated mechanism for CO/H 2 O/H 2 /O 2 , CH 2 O, and CH 3 OH oxidation. Important modifications include recent revisions for the hydrogen-oxygen submechanism (Li et al., Int J Chem Kinet 2004, 36, 565), an updated submechanism for methanol reactions, and kinetic and thermochemical parameter modifications based upon recently published information. New rate constant correlations are recommended for CO + OH = CO 2 + H (R23) and HCO + M = H + CO + M (R24), motivated by a new identification of the temperatures over which these rate constants most affect laminar flame speed predictions (Zhao et al., Int J Chem Kinet 2005, 37, 282). The new weighted least-squares fit of literature experimental data for (R23) yields k 23 = 2.23 × 10 5 T 1.89 exp(583/T ) cm 3 /mol/s and reflects significantly lower rate constant values at low and intermediate temperatures in comparison to another recently recommended correlation and theoretical predictions. The weighted least-squares fit of literature results for (R24) yields k 24 = 4.75 × 10 11 T 0.66 exp(−7485/T ) cm 3 /mol/s, which predicts values within uncertainties of both prior and new (Friedrichs et al., Phys Chem Chem Phys 2002, 4, 5778; DeSain et al., Chem Phys Lett 2001, 347, 79) measurements. Use of either of the data correlations reported in and DeSain et al. (2001) for this reaction significantly degrades laminar flame speed predictions for oxygenated fuels as well as for other hydrocarbons. The present C 1 /O 2 mechanism compares favorably against a wide range of experimental conditions for laminar premixed flame speed, shock tube ignition delay, and flow reactor species time history data at each level of hierarchical development. Very good agreement of the model predictions with all of the experimental measurements is demonstrated.

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An updated H 2 /O 2 kinetic model based on that of Li et al. (Int J Chem Kinet 36, 2004, 566-575) is presented and tested against a wide range of combustion targets. The primary motivations of the model revision are to incorporate recent improvements in rate constant treatment and resolve discrepancies between experimental data and predictions using recently published kinetic models in dilute, high-pressure flames. Attempts are made to identify major remaining sources of uncertainties, in both the reaction rate parameters and the assumptions of the kinetic model, affecting predictions of relevant combustion behavior. With regard to model parameters, present uncertainties in the temperature and pressure dependence of rate constants for HO 2 formation and consumption reactions are demonstrated to substantially affect predictive capabilities at high-pressure, low-temperature conditions. With regard to model assumptions, calculations are performed to investigate several reactions/processes that have not received much attention previously. Results from ab initio calculations and modeling studies imply that inclusion of H + HO 2 = H 2 O + O in the kinetic model might be warranted, though further studies are necessary to ascertain its role in combustion modeling. In addition, it appears that characterization of nonlinear bath-gas mixture rule behavior for H + O 2 (+ M) = HO 2 (+ M) in multicomponent bath gases might be necessary to predict high-pressure flame speeds within ∼15%. The updated model is tested against all of the previous validation targets considered by Li et al. as well as new targets from a number of recent studies. Special attention is devoted to establishing a context for evaluating model performance against experimental data by careful consideration of uncertainties in measurements, initial conditions, and physical modelCorrespondence to: Michael P. Burke;

The unimolecular decomposition reaction of dimethyl ether (DME) was studied theoretically using RRKM/master equation calculations. The calculated decomposition rate is significantly different from that utilized in prior work (Fischer et al., Int J Chem Kinet 2000, 32, 713-740; Curran et al., Int J Chem Kinet 2000, 32, 741-759). DME pyrolysis experiments were performed at 980 K in a variable-pressure flow reactor at a pressure of 10 atm, a considerably higher pressure than previous validation data. Both unimolecular decomposition and radical abstraction are significant in describing DME pyrolysis, and hierarchical methodology was applied to produce a comprehensive high-temperature model for pyrolysis and oxidation that includes the new decomposition parameters and more recent small molecule/radical kinetic and thermochemical data. The high-temperature model shows improved agreement against the new pyrolysis data and the wide range of high-temperature oxidation data modeled in prior work, as well as new low-pressure burner-stabilized species profiles (Cool et al., Proc Combust Inst 2007, 31, 285-294) and laminar flame data for DME/methane mixtures (Chen et al., Proc Combust Inst 2007, 31, 1215-1222. The high-temperature model was combined with low-temperature oxidation chemistry (adopted from Fischer et al., Int J Chem Kinet 2000, 32, 713-740), with some modifications to several important reactions. The revised construct shows good agreement against high-as well as low-temperature flow reactor and jet-stirred reactor data, shock tube ignition delays, and laminar flame species as well as flame speed measurements. C 2007 Wiley Periodicals, Inc. Int J Chem Kinet 40:

The oxidation of methyl formate (CH 3 OCHO) has been studied in three experimental environments over a range of applied combustion relevant conditions: 1. A variable-pressure flow reactor has been used to quantify reactant, major intermediate and product species as a function of residence time at 3 atm and 0.5% fuel concentration for oxygen/fuel stoichiometries of 0.5, 1.0, and 1.5 at 900 K, and for pyrolysis at 975 K. 2. Shock tube ignition delays have been determined for CH 3 OCHO/O 2 /Ar mixtures at pressures of ≈ 2.7, 5.4, and 9.2 atm and temperatures of 1275-1935 K for mixture compositions of 0.5% fuel (at equivalence ratios of 1.0, 2.0, and 0.5) and 2.5% fuel (at an equivalence ratio of 1.0). 3. Laminar burning velocities of outwardly propagating spherical CH 3 OCHO/air flames have been determined for stoichiometries ranging from 0.8-1.6, at atmospheric pressure using a pressure-release-type high-pressure chamber.A detailed chemical kinetic model has been constructed, validated against, and used to interpret these experimental data. The kinetic model shows that methyl formate oxidation proceeds through concerted elimination reactions, principally forming methanol and carbon monoxide as well as through bimolecular hydrogen abstraction reactions. The relative importance of elimination versus abstraction was found to depend on the particular environment. In general, methyl formate is consumed exclusively through molecular decomposition in shock tube environments, while at flow reactor and freely propagating premixed flame conditions, there is significant competition between hydrogen abstraction and concerted elimination channels. It is suspected that in diffusion flame configurations the elimination channels contribute more significantly than in premixed environments. C