Chemical kinetic modeling of hydrocarbon combustion

This chapter is a critical survey of reaction rate coefficient data important in describing high-temperature combustion of H2, CO, and small hydrocarbons up to C4. A recommended reaction mechanism and rate coefficient set is presented. The approximate temperature range for this mechanism is from 1200 to 2500 K, which therefore excludes detailed consideration of cool flames, low-temperature ignition, or reactions of organic peroxides or peroxy radicals. Low-temperature rate-coefficient data are presented, however, when they contribute to defining or understanding high-temperature rate coefficients. Because our current knowledge of reaction kinetics is incomplete, this mechanism is inadequate for very fuel-rich conditions (see Warnatz et al., 1982). For the most part, reactions are considered only when their rates may be important for modeling combustion processes. This criterion eliminates considering many reactions among minor species present at concentrations so low that reactions of these species cannot play an essential part in combustion processes. The philosophy in evaluating the rate-coefficient data was to be selective rather than exhaustive: Recent results obtained with experimental methods capable of measuring isolated elementary reaction rate parameters directly were preferred, while results obtained using computer simulations of complex reacting systems were considered only when sensitivity to a particular elementary reaction was demonstrated or when direct measurements are not available. Theoretical results were not considered.

Rate Coefficients in the C/H/O System

Dimethyl ether reaction kinetics at high temperature were studied in two different flow reactors under highly dilute conditions. Pyrolysis of dimethyl ether was studied in a variable-pressure flow reactor at 2.5 atm and 1118 K. Studies were also conducted in an atmospheric pressure flow reactor at about 1085 K. These experiments included trace-oxygen-assisted pyrolysis, as well as full oxidation experiments, with the equivalence ratio (ϕ) varying from 0.32 ≤ ϕ ≤ 3.4. On-line, continuous, extractive sampling in conjunction with Fourier Transform Infra-Red, Non-Dispersive Infra-Red (for CO and CO2) and electrochemical (for O2) analyses were performed to quantify species at specific locations along the axis of the turbulent flow reactors. Species concentrations were correlated against residence time in the reactor and species evolution profiles were compared to the predictions of a previously published detailed kinetic mechanism. Some changes were made to the model in order to improve agreement with the present experimental data. However, the revised model continues to reproduce previously reported high-temperature jet-stirred reactor and shock tube results. © 2000 John Wiley & Sons, Inc. Int J Chem Kinet: 32: 713–740, 2000

The reaction kinetics of dimethyl ether. I: High‐temperature pyrolysis and oxidation in flow reactors

A detailed chemical kinetic model has been used to study dimethyl ether (DME) oxidation over a wide range of conditions Experimental results obtained in a jet-stirred reactor (JSR) at I and 10 atm, 02 < 0 < 25, and 800 < T < 1300 K were modeled, in addition to those generated in a shock tube at 13 and 40 bar, 0 = 10 and 650 :5 T :5 1300 K The JSR results are particularly valuable as they include concentration profiles of reactants, intermediates and products pertinent to the oxidation of DME These data test the Idnetic model severely, as it must be able to predict the correct distribution and concentrations of intermediate and final products formed in the oxidation process Additionally, the shock tube results are very useful, as they were taken at low temperatures and at high pressures, and thus undergo negative temperature dependence (NTC) behavior This behavior is characteristic of the oxidation of saturated hydrocarbon fuels, (eg the primary reference fuels, n-heptane and iso- octane) under similar conditions The numerical model consists of 78 chemical species and 336 chemical reactions The thermodynamic properties of unknown species pertaining to DME oxidation were calculated using THERM

/pdf/a-wide-range-modeling-study-of-dimethyl-ether-oxidation-2w5vtl2qna.pdf

A wide range modeling study of dimethyl ether oxidation

A detailed chemical kinetic model has been used to study dimethyl ether (DME) oxidation over a wide range of conditions. Experimental results obtained in a jet-stirred reactor (JSR) at I and 10 atm, 0.2 < 0 < 2.5, and 800 < T < 1300 K were modeled, in addition to those generated in a shock tube at 13 and 40 bar, 0 = 1.0 and 650 :5 T :5 1300 K. The JSR results are particularly valuable as they include concentration profiles of reactants, intermediates and products pertinent to the oxidation of DME. These data test the Idnetic model severely, as it must be able to predict the correct distribution and concentrations of intermediate and final products formed in the oxidation process. Additionally, the shock tube results are very useful, as they were taken at low temperatures and at high pressures, and thus undergo negative temperature dependence (NTC) behavior. This behavior is characteristic of the oxidation of saturated hydrocarbon fuels, (e.g. the primary reference fuels, n-heptane and iso- octane) under similar conditions. The numerical model consists of 78 chemical species and 336 chemical reactions. The thermodynamic properties of unknown species pertaining to DME oxidation were calculated using THERM.

/pdf/wide-range-modeling-study-of-dimethyl-ether-oxidation-pnag57ojwu.pdf

Wide range modeling study of dimethyl ether oxidation

Kinetic isotope effects in the reactions of hydrogen and deuterium atoms with dimethyl ether and methanol

The kinetics of the reaction of O + CH3OCH3 were investigated using fast-flow apparatus equipped with ESR and mass-spectrometric detection. The concentration of O(3P) atoms to CH3OCH3 was varied over an unusually large range. The rate constant for reaction 






was found to be k = (5.0 ± 1.0) × 1012 exp [(−2850 ± 200/RT)] cm3 mole−1 sec−1. The reaction O + CH3OH was studied using ESR detection. Based on an assumed stoichiometry of two oxygen atoms consumed per molecule of CH3OH which reacts, we obtain a value of k = (1.70 ± 0.66) × 1012 exp [(−2,280 ± 200/RT)] cm3 mole−1 sec−1 for the reaction 






The results obtained in this study are compared with the results from other workers on these reactions. The observation of essentially equal activation energies in these two reactions is indicative of approximately equal CH bond strengths in CH3OCH3 and CH3OH. This is in agreement with recent measurements of these bond energies.

The kinetics of the reactions of O(3P) atoms with dimethyl ether and methanol

The room temperature vacuum uv photolysis of dimethyl ether at 1470 A has been investigated. The main products were found to be H2, H2CO, C2H6, and CH4. In addition, some CH3OCH2CH2OCH3 and CH3CH2OCH3 were identified. The effects of free radical scavengers (C2D4 and H2S) and added inert gas (C2F6) were studied. Molecular elimination processes were found to account for a relatively small fraction of the total product yield. A mechanism has been proposed to account for the major experimental observations.

James F. Meagher

Papers

Kinetic isotope effects in the reactions of hydrogen and deuterium atoms with dimethyl ether and methanol

The kinetics of the reactions of O(3P) atoms with dimethyl ether and methanol

Photochemistry of Dimethyl Ether at 1470 Å

Kinetik der rk. von o((3)p)-atomen mit dimethylaether und methanol