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

Oxy-fuel combustion of pulverized coal: Characterization, fundamentals, stabilization and CFD modeling

Hierarchical and comparative kinetic modeling of laminar flame speeds of hydrocarbon and oxygenated fuels

An updated H2/O2 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 HO2 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 + HO2 = H2O + 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 + O2(+ M) = HO2(+ 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 model assumptions. For example, ignition delay times in shock tubes are shown to be sensitive to potential impurity effects, which have been suggested to accelerate early radical pool growth in shock tube speciation studies. In addition, speciation predictions in burner-stabilized flames are found to be more sensitive to uncertainties in experimental boundary conditions than to uncertainties in kinetics and transport. Predictions using the present model adequately reproduce previous validation targets and show substantially improved agreement against recent high-pressure flame speed and shock tube speciation measurements. Comparisons of predictions of several other kinetic models with the experimental data for nearly the entire validation set used here are also provided in the Supporting Information. © 2011 Wiley Periodicals, Inc. Int J Chem Kinet 44: 444–474, 2012

Comprehensive H2/O2 kinetic model for high-pressure combustion

Alcohol combustion chemistry

Two global multistep schemes, the two-step mechanism of Westbrook and Dryer (WD) and the four-step mechanism of Jones and Lindstedt (JL), have been refined for oxy-fuel conditions. Reference calculations were conducted with a detailed chemical kinetic mechanism, validated for oxy-fuel combustion conditions. In the modification approach, the initiating reactions involving hydrocarbon and oxygen were retained, while modifying the H2−CO−CO2 reactions in order to improve prediction of major species concentrations. The main attention has been to capture the trend and level of CO predicted by the detailed mechanism as well as the correct equilibrium concentration. A CFD analysis of a propane oxy-fuel flame has been performed using both the original and modified mechanisms. Compared to the original schemes, the modified WD mechanism improved the prediction of the temperature field and of CO in the post flame zone, while the modified JL mechanism provided a slightly better prediction of CO in the flame zone.

Global Combustion Mechanisms for Use in CFD Modeling under Oxy-Fuel Conditions

Article on experimental measurements and kinetic modeling of CO/H₂/O₂/NOₓ conversion at high pressure.

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Experimental measurements and kinetic modeling of CO/H2/O2/NOx conversion at high pressure

Sensitizing effects of NOx on CH4 oxidation at high pressure

It is well established from experiments in premixed, laminar flames, jet-stirred reactors, flow reactors, and batch reactors that SO 2 acts to catalyze hydrogen atom removal at stoichiometric and reducing conditions. However, the commonly accepted mechanism for radical removal, SO 2  + H(+M) ⇌ HOSO(+M), HOSO + H/OH ⇌ SO 2  + H 2 /H 2 O, has been challenged by recent theoretical and experimental results. Based on ab initio calculations for key reactions, we update the kinetic model for this chemistry and re-examine the mechanism of fuel/SO 2 interactions. We find that the interaction of SO 2 with the radical pool is more complex than previously assumed, involving HOSO and SO, as well as, at high temperatures also HSO, SH, and S. The revised mechanism with a high rate constant for H + SO 2 recombination and with SO + H 2 O, rather than SO 2  + H 2 , as major products of the HOSO + H reaction is in agreement with a range of experimental results from batch and flow reactors, as well as laminar flames.

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Mechanisms of Radical Removal by SO2

A detailed chemical kinetic model for oxidation of C 2 H 4 in the intermediate temperature range and high pressure has been developed and validated experimentally. New ab initio calculations and RRKM analysis of the important C 2 H 3  + O 2 reaction was used to obtain rate coefficients over a wide range of conditions (0.003–100 bar, 200–3000 K). The results indicate that at 60 bar and medium temperatures vinyl peroxide, rather than CH 2 O and HCO, is the dominant product. The experiments, involving C 2 H 4 /O 2 mixtures diluted in N 2 , were carried out in a high pressure flow reactor at 600–900 K and 60 bar, varying the reaction stoichiometry from very lean to fuel-rich conditions. Model predictions are generally satisfactory. The governing reaction mechanisms are outlined based on calculations with the kinetic model. Under the investigated conditions the oxidation pathways for C 2 H 4 are more complex than those prevailing at higher temperatures and lower pressures. The major differences are the importance of the hydroxyethyl (CH 2 CH 2 OH) and 2-hydroperoxyethyl (CH 2 CH 2 OOH) radicals, formed from addition of OH and HO 2 to C 2 H 4 , and vinyl peroxide, formed from C 2 H 3  + O 2 . Hydroxyethyl is oxidized through the peroxide HOCH 2 CH 2 OO (lean conditions) or through ethenol (low O 2 concentration), while 2-hydroperoxyethyl is converted through oxirane.

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Christian Lund Rasmussen

Papers

Global Combustion Mechanisms for Use in CFD Modeling under Oxy-Fuel Conditions

Experimental measurements and kinetic modeling of CO/H2/O2/NOx conversion at high pressure

Sensitizing effects of NOx on CH4 oxidation at high pressure

Mechanisms of Radical Removal by SO2

Experimental and Kinetic Modeling Study of C2H4 Oxidation at High Pressure