To investigate the initial chemical events associated with high-temperature gas-phase oxidation of hydrocarbons, we have expanded the ReaxFF reactive force field training set to include additional transition states and chemical reactivity of systems relevant to these reactions and optimized the force field parameters against a quantum mechanics (QM)-based training set. To validate the ReaxFF potential obtained after parameter optimization, we performed a range of NVT−MD simulations on various hydrocarbon/O2 systems. From simulations on methane/O2, o-xylene/O2, propene/O2, and benzene/O2 mixtures, we found that ReaxFF obtains the correct reactivity trend (propene > o-xylene > methane > benzene), following the trend in the C−H bond strength in these hydrocarbons. We also tracked in detail the reactions during a complete oxidation of isolated methane, propene, and o-xylene to a CO/CO2/H2O mixture and found that the pathways predicted by ReaxFF are in agreement with chemical intuition and our QM results. We o...

ReaxFF Reactive Force Field for Molecular Dynamics Simulations of Hydrocarbon Oxidation

Progress and recent trends in homogeneous charge compression ignition (HCCI) engines

A detailed chemical kinetic mechanism has been developed to describe the oxidation of small hydrocarbon and oxygenated hydrocarbon species. The reactivity of these small fuels and intermediates is of critical importance in understanding and accurately describing the combustion characteristics, such as ignition delay time, flame speed, and emissions of practical fuels. The chosen rate expressions have been assembled through critical evaluation of the literature, with minimum optimization performed. The mechanism has been validated over a wide range of initial conditions and experimental devices, including flow reactor, shock tube, jet-stirred reactor, and flame studies. The current mechanism contains accurate kinetic descriptions for saturated and unsaturated hydrocarbons, namely methane, ethane, ethylene, and acetylene, and oxygenated species; formaldehyde, methanol, acetaldehyde, and ethanol.

A Hierarchical and Comparative Kinetic Modeling Study of C1 − C2 Hydrocarbon and Oxygenated Fuels

https://hal.archives-ouvertes.fr/hal-00848875/document

A comprehensive detailed chemical kinetic reaction mechanism for combustion of n-alkane hydrocarbons from n-octane to n-hexadecane

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/H2O/H2/O2, CH2O, and CH3OH 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 = CO2 + 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 k23 = 2.23 × 105T1.89exp(583/T) cm3/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 k24 = 4.75 × 1011T0.66exp(−7485/T) cm3/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 Friedrichs et al. (2002) 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 C1/O2 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. © 2007 Wiley Periodicals, Inc. 39: 109–136, 2007

A comprehensive kinetic mechanism for CO, CH2O, and CH3OH combustion

Ethylene oxidation and pyrolysis was modeled using a comprehensive kinetic reaction mechanism. This mechanism is an updated version of one developed earlier. It includes the most recent findings concerning the kinetics of the reactions involved in the oxidation of ethylene. The proposed mechanism was tested against ethylene oxidation experimental data (molecular species concentration profiles) obtained in jet stirred reactors (1–10 atm, 880–1253 K), ignition delay times measured in shock tubes (0.2–12 atm, 1058–2200 K) and ethylene pyrolysis data in shock tube (2–6 atm, 1700–2200 K). The general prediction of concentration profiles of minor species formed during ethylene oxidation is improved in the present model by using more accurate kinetic data for several reactions (principally: HO2 + HO2 H2O2 + O2, C2H4 + OH C2H3 + H2O, C2H2 + OH Products, C2H3 C2H2 + H).

Ethylene pyrolysis and oxidation: A kinetic modeling study

Ethane oxidation in jet-stirred reactor has recently been investigated at high temperature (800–1200 K) in the pressure range 1–10 atm and molecular species (H2, CO, CO2, CH4, C2H2, C2H4, C2H6) concentration profiles were obtained by probe sampling and GC analysis. Ethane oxidation was modeled using a comprehensive kinetic reaction mechanism including the most recent findings concerning the kinetics of the reactions involved in the oxidation of C1C4 hydrocarbons. The proposed mechanism is able to reproduce experimental data obtained in our high-pressure jet stirred reactor and ignition delay times measured in shock tube in the pressure range 1–13 atm, for temperatures extending from 800 to 2000 K and equivalence ratios of 0.1 to 2. It is also able to reproduce atoms concentrations (H,O) measured in shock tube at ≈2 atm. The same detailed kinetic mechanism can also be used to model the oxidation of methane, ethylene, propyne, and allene in similar conditions.

Kinetics of ethane oxidation

The oxidation of propene was studied in a jet stirred flow reactor in the temperature range 900-1200 K at pressures extending from 1 to 8 atm for a wide range of fuel-oxygen equivalence ratios (0.15-4.0). A computer program has been developed to model the experimental data by using a chemical kinetic reaction mechanism. A direct method to determine the first-order sensitivities of the mole fraction of each species with respect to the rate constants was used to develop the kinetic scheme. The present chemical kinetic reaction mechanism is able to reproduce the experimental results, although some discrepancies are observed for the minor products.

Experimental study and kinetic modeling of propene oxidation in a jet stirred flow reactor

Propane oxidation in jet-stirred reactor was modeled using a comprehensive kinetic reaction mechanism including the most recent findings concerning the kinetics of the reactions involved in the oxidation of C1C4 hydrocarbons. The present detailed mechanism is able to reproduce experimental species concentration profiles obtained in our high-pressure jet-stirred reactor (900 ⩽ T/K ⩽ 1200; 1 ⩽ P/atm ⩽ 10; 0.15 ⩽ ϕ ⩽ 4) and in a turbulent flow reactor at 1 atm; ignition delay times measured in shock tube (1200 ⩽ T/K ⩽ 1700; 2 ⩽ P/atm ⩽ 15; 0.125 ⩽ ϕ ⩽ 2); H-atoms concentrations measured in shock tube during the pyrolysis of propane and burning velocities of freely propagating premixed propane-air laminar flames. The computed results are discussed in terms of pressure and equivalence ratio (ϕ) effects on propane oxidation. The same detailed kinetic reaction mechanism can also be used to model the oxidation of methane, ethylene, ethane, and propene in similar conditions. © John Wiley & Sons, Inc.

Kinetic modeling of propane oxidation and pyrolysis

The kinetics of the oxidation of natural gas and blends (CH 4 /C 2 H 6 , CH 4 /C 3 H 8 , CH 4 /C 2 H 6 /C 3 H 8 ) hasbeen studied in a jet-stirred reactor (800≤ T/K ≤1240, 1≤ P /atm≤10, 0.1≤equivalence ratio≤1.5). The concentration profiles of reactants, intermediates, and products measured in a jet-stirred reactor (JSR) have been used to validate a detailed kinetic reaction mechanism. Literature ignition delay times measured in shock tube have also been modeled. A generally good agreement between the data and the model is found. The same mechanism has also been used to successfully represent the oxidation of methane, ethyne, ethene, ethane, propene, propane, n -butane, and 1-butene in various conditions including JSR, shock tube, and flame. The present study clearly shows the importance of trace hydrocarbons in the oxidation of methane. The computations indicate that the oxidation of methane is initiated by its reaction with O 2 when no other hydrocarbon is present. In natural gas and blends, higher hydrocarbons react before methane, leading to the formation of OH, H, and O radicals, which in turn initiate methane oxidation. This work demonstrates that methane cannot be used safely to represent the kinetics of natural gas combustion. However, simple blends like methane-propane or methane-ethane-propane could be used.

J. C. Boettner

Papers

Ethylene pyrolysis and oxidation: A kinetic modeling study

Kinetics of ethane oxidation

Experimental study and kinetic modeling of propene oxidation in a jet stirred flow reactor

Kinetic modeling of propane oxidation and pyrolysis

Natural gas and blends oxidation and ignition: Experiments and modeling