Experimental and modeling study of the oxidation of isobutene

This article describes an experimental and modeling study of the oxidation of isobutene. The low-temperature oxidation was studied in a continuous-flow stirred-tank reactor operated at constant temperature (from 833 to 913 K) and pressure (1 atm), with fuel equivalence ratios from 3 to 6 and space times ranging from 1 to 10 s corresponding to isobutene conversion yields from 1 to 50%. The main carbon containing products were analyzed by gas chromatography. The ignition delays of isobutene-oxygen-argon mixtures with fuel equivalence ratios from 1 to 3 were measured behind shock waves. Reflected shock waves permitted to obtain temperatures from 1230 to 1930 K and pressures from 9.5 to 10.5 atm. A mechanism has been proposed to reproduce the profiles obtained for the reactants consumption and the products formation during the slow oxidation and to compute the ignition delays in the shock tube. Simulations were performed using CHEMKIN II. A correct agreement between the simulated values and the experimental data has been obtained in both apparatuses. The main reaction paths have been determined for both series of measurements by a sensitivity and rate of production analysis. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 629–640, 1998     

Experimental and modeling study of the oxidation of benzene

This paper describes an experimental and modeling study of the oxidation of benzene. The low‐temperature oxidation was studied in a continuous flow stirred tank reactor with carbon‐containing products analyzed by gas chromatography. The following experimental conditions were used: 923 K, 1 atm, fuel equivalence ratios from 1.9 to 3.6, concentrations of benzene from 4 to 4.5%, and residence times ranging from 1 to 10 s corresponding to benzene conversion yields from 6 to 45%. The ignition delays of benzene–oxygen–argon mixtures with fuel equivalence ratios from 1 to 3 were measured behind shock waves. Reflected shock waves permitted to obtain temperatures from 1230 to 1970 K and pressures from 6.5 to 9.5 atm. A detailed mechanism has been proposed and allows us to reproduce satisfactorily our experimental results, as well as some data of the literature obtained in other conditions, such as in a plug flow reactor or in a laminar premixed flame. The main reaction paths have been determined for the four series of measurements by sensitivity and flux analyses. © 2003 Wiley Periodicals, Inc. Int J Chem Kinet 35: 503–524, 2003     

Experimental and modeling study of the oxidation of cyclohexene

Ignition delays of cyclohexene–oxygen–argon mixtures were measured behind shock. Mixtures contained 1 or 2% of hydrocarbons for equivalence ratios ranging from 0.5 to 2. Reflected shock waves permitted to obtain temperatures from 1050 to 1520 K and pressures from 7.7 to 9.1 atm. The experimental results exhibit an Arrhenius variation vs. temperature. A detailed mechanism of the combustion of cyclohexene has been written in the line of the mechanism developed previously for the reaction of C₃? C₄ unsaturated hydrocarbons (propyne, allene, 1,3‐butadiene, butynes); it is based on recent kinetic data values published in the literature and is consistent with thermochemistry. This mechanism has been validated by comparing the results of the simulations to the experimental results obtained for ignition delays. The main reaction pathways have been derived from flow rate and sensitivity analyses for the different temperature areas studied. © 2003 Wiley Periodicals, Inc. Int J Chem Kinet 35: 273–285, 2003     

Experimental and modeling study of the oxidation of toluene

This paper describes an experimental and modeling study of the oxidation of toluene. The low‐temperature oxidation was studied in a continuous flow stirred tank reactor with carbon‐containing products analyzed by gas chromatography under the following experimental conditions: temperature from 873 to 923 K, 1 bar, fuel equivalence ratios from 0.45 to 0.91, concentrations of toluene from 1.4 to 1.7%, and residence times ranging from 2 to 13 s corresponding to toluene conversion from 5 to 85%. The ignition delays of toluene–oxygen–argon mixtures with fuel equivalence ratios from 0.5 to 3 were measured behind reflected shock waves for temperatures from 1305 to 1795 K and at a pressure of 8.7 ± 0.7 bar. A detailed kinetic mechanism has been proposed to reproduce our experimental results, as well as some literature data obtained in other shock tubes and in a plug flow reactor. The main reaction paths have been determined by sensitivity and flux analyses. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 37: 25–49, 2005     

Experimental and modeling study of methyl cyclohexane pyrolysis and oxidation

Although the combustion chemistry of aliphatic hydrocarbons has been extensively documented, the oxidation of cyclic hydrocarbons has been studied to a much lesser extent. To provide a deeper understanding of the combustion chemistry of naphthenes, the oxidation of methylcyclohexane was studied in a series of high-temperature shock tube experiments. Ignition delay times for a series of mixtures, of varying methylcyclohexane/oxygen equivalence ratios (phi=0.5, 1.0, 2.0), were measured over reflected shock temperatures of 1200-2100 K and reflected shock pressures of 1.0, 2.0, and 4.0 atm. A detailed chemical kinetic mechanism has been assembled to simulate the shock tube results and flow reactor experiments, with good agreement observed.     

Experimental and chemical kinetic modeling study of 3-pentanone oxidation

Shock tube ignition delay times have been measured for 3-pentanone at a reflected shock pressure of 1 atm (±2%), in the temperature range 1250-1850 K, at equivalence ratios of 0.5-2.0 for O(2) mixtures in argon with fuel concentrations varying from 0.875 to 1.3125%. Laminar flame speeds have also been measured at an initial pressure of 1 atm over an equivalence ratio range. Complementary to previous studies [Pichon S., Black, G., Chaumeix, N., Yahyaoui, M., Simmie, J. M., Curran, H. J., Donohue, R. Combust. Flame, 2009, 156, 494-504; Serinyel, Z.; Black, G.; Curran, H. J.; Simmie, J. M. Combustion Sci. Tech., 2010, 182, 574-587], laminar flame speeds of 2-butanone have also been measured, and relative reactivities of these ketones have been compared and discussed. A chemical kinetic submechanism describing the oxidation of 3-pentanone has been developed and detailed in this paper; rate constants for unimolecular fuel decomposition reactions have been treated for falloff in pressure with nine-parameter fits using the Troe Formulism. Both compounds treated in this work may be used as fuel tracers, thus further ignition delay time measurements have been carried out by adding 3-pentanone to n-heptane in order to test the effect of the blend on ignition delay timing. It was found that the autoignition characteristics of n-heptane remained unaffected in the presence of 15% 3-pentanone in the fuel, consistent with results obtained using acetone and 2-butanone [Pichon S., Black, G., Chaumeix, N., Yahyaoui, M., Simmie, J. M., Curran, H. J., Donohue, R. Combust. Flame, 2009, 156, 494-504; Serinyel, Z.; Black, G.; Curran, H. J.; Simmie, J. M. Combustion Sci. Tech., 2010, 182, 574-587].     

Experimental and modeling study of shock‐tube oxidation of acetylene

Nine mixtures of acetylene and oxygen diluted in argon were studied behind reflected shock waves at temperatures of 1150–2132 K and pressures of 0.9–1.9 atm. Initial compositions were varied from very fuel‐lean to moderately fuel‐rich, covering equivalence ratios of 0.0625–1.66. Two more mixtures with added ethylene were used to boost the sensitivity to reactions of vinyl oxidation. The progress of reaction was monitored by laser absorption of CO molecules. The collected experimental data were subjected to extensive detailed chemical kinetics analysis. The initial kinetic model was assembled based on recent literature data and then optimized using the solution mapping technique. The analysis was extended to include recent experimental observations of Hidaka and co‐workers (Combust Flame 1996, 107, 401). The derived model reproduces closely both sets of experimental data, the result obtained by modifying nine rate coefficients and three enthalpies of formation of intermediate species. The identified parameter tradeoffs and justification for the changes are discussed. © 2003 Wiley Periodicals, Inc. Int J Chem Kinet 35: 391–414, 2003     

Experimental and kinetic modeling study of the oxidation of cyclopentane and methylcyclopentane at atmospheric pressure

Cyclopentane and methylcyclopentane oxidation was investigated in a jet-stirred reactor at atmospheric pressure, over temperatures ranging from 900 to 1250 K, for fuel-lean, stoichiometric, and fuel-rich mixtures at a constant residence time of 70 ms. The initial mole fraction of both fuels was kept constant at 1000 ppm. The reactants were highly diluted by a flow of nitrogen to ensure thermal homogeneity. Samples of the reacting mixture were analyzed online and off-line by Fourier transform infrared spectroscopy and gas chromatography. A detailed kinetic mechanism consisting of 590 species involved in 3469 reactions was developed, and simulation results were compared to these new experimental data and previously reported ignition delays. Reaction pathways analysis as well as sensitivity analyses were performed to get insights into the differences observed during the oxidation process of cyclopentane and methylcyclopentane.     

Experimental and modeling study of the oxidation of 1‐pentene at high temperature

Ignition delay times of 1‐pentene–oxygen–argon mixtures have been measured behind shock wave, the onset of ignition being detected by OH radical emission. Mixtures contained 1 or 2% of hydrocarbon for equivalence ratios ranging from 0.5 to 2. Reflected shock waves allowed temperatures from 1130 to 1620 K and pressures from 7.3 to 9.5 atm to be obtained. A detailed mechanism of combustion of 1‐pentene has been automatically generated using EXGAS software. This mechanism has been validated by comparing the results of the simulations to the experimental ignition delay times. The main reaction pathways have been derived from flow rate and sensitivity analyses at different temperatures. Comparisons with 1‐butene and 1‐hexene in the same conditions show that 1‐pentene has a higher reactivity which seems to be due to its decomposition to give ethyl radicals, which rapidly yields very reactive hydrogen atoms, while the decomposition of 1‐butene and 1‐hexene leads to less reactive methyl radicals. © 2005 Wiley Periodicals, Inc. Int J Chem Kinet 37: 451–463, 2005     

Experimental investigation of the molecular ions of the xylenes

A mass spectrometric method of distinguishing between molecular ions of the three isomeric xylenes (dimethylbenzenes) was sought, in light of recent findigs that photoexcited ions could be distinguished via measurements of kinetic energy release accompanying expulsion of a methyl radical. Provided the molecular ions are formed with low internal energies, reproducible differences were found between relative intensities of collision induced reactions of higher critical energies, than for methyl expulsion. These differences exist both for collision energies in the kilovolt range (double focusing mass spectrometers) and in the range of a few tens of volts (triple quadrupole instrument). Though statistically significant, these differences were small. The mechanism of isomerization and fragmentation was investigated via isotopic labelling studies and measurements of kinetic energy release. Most of the present findings can be rationalized in terms of the most recent version of established mechanisms for reactions of ionized methylbenzenes.     

A comprehensive modeling study of hydrogen oxidation

A detailed kinetic mechanism has been developed to simulate the combustion of H₂/O₂ mixtures, over a wide range of temperatures, pressures, and equivalence ratios. Over the series of experiments numerically investigated, the temperature ranged from 298 to 2700 K, the pressure from 0.05 to 87 atm, and the equivalence ratios from 0.2 to 6. Ignition delay times, flame speeds, and species composition data provide for a stringent test of the chemical kinetic mechanism, all of which are simulated in the current study with varying success. A sensitivity analysis was carried out to determine which reactions were dominating the H₂/O₂ system at particular conditions of pressure, temperature, and fuel/oxygen/diluent ratios. Overall, good agreement was observed between the model and the wide range of experiments simulated. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36: 603–622, 2004     

Shock-tube and modeling study of chloroethane pyrolysis and oxidation

The high-temperature pyrolysis and oxidation of chloroethane were studied behind reflected shock waves using single-pulse, time-resolved IR absorption (3.39 μm), time-resolved UV absorption (306.7 nm), and time-resolved IR emission (4.24 μm) methods. The studies were performed over the temperature range 900–1650 K at total pressures between 0.8 and 3.2 atm. From a computer simulation study, a 201-reaction mechanism that could explain all of our data was constructed. The reactions at high temperatures were discussed in detail. It was found that, in the chloroethane pyrolysis and oxidation under our experimental conditions, reactions (1)–(7) and (9) and the submechanism of ethylene were important to predict our data. © 2008 Wiley Periodicals, Inc. Int J Chem Kinet 40: 320–339, 2008     

Experimental and modeling study of the oxidation of 1‐butyne and 2‐butyne

Ignition delays were measured behind shock waves in the cases of hydrocarbon–oxygen–argon mixtures containing 1‐butyne or 2‐butyne (1 or 2% of hydrocarbons for equivalence ratios from 0.5 to 2). Reflected shock waves permitted to obtain temperatures from 1100 to 1600 K and pressures from 6.3 to 9.1 atm. A detailed mechanism of the reactions of 1‐butyne and 2‐butyne has been explained in the line of the mechanism developed previously for the reaction of C₃–C₄ unsaturated hydrocarbons (propyne, allene, 1,3‐butadiene) [Int J chem Kin 1999, 31, 361]. It is based on the most recent kinetic data values published in the literature and is consistent with thermochemistry. This mechanism has been validated by comparing the results of our simulations to the experimental results obtained for ignition delays in our shock tube and to measurements of species obtained during thermal decomposition [Int J Chem Kin 1995, 27, 321; J Phys Chem 1993, 97, 10977]. The main reaction pathways have been derived from flow‐rate and sensitivity analyses. © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 34: 172–183, 2002; DOI 10.1002/kin.10035     

Mechanism of oxidation of xylenes with Pd(II) complexes

Conclusions Oxidation of xylenes with Pd(II) complexes in acidic medium is possible according to two pathways: a) electrophilic substitution in the arene ring with the formation of an organometalic intermediate and b) one-electron transfer from the arene to the palladium atom with the intermediacy of the arene cation-radical. The relative contribution of each pathway depends on the nature of the arene and on the acidity of the medium.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 10, pp. 2167–2174, October, 1985.     

Experimental and modeling study of the autoignition of cyclopentene

Ignition delay times of cyclopentene–oxygen–argon mixtures were measured behind reflected shock waves. Mixtures contained 0.5% or 1% of hydrocarbons for equivalence ratios ranging from 0.5 to 1.5. Reflected shock wave conditions were as follows: temperatures from 1300 to 1700 K and pressures from 7 to 9 atm. When compared with the previous results obtained under similar conditions, it can be observed that the reactivity of cyclopentene is much lower than that of cyclohexene, but very close to that of cyclopentane. A kinetic mechanism recently proposed for the combustion of cyclopentene in a flame has been used to model these results, and a satisfactory agreement is obtained. The main reaction pathways have been derived from the flow rate, simulated temporal profiles of products, and sensitivity analyses. © 2007 Wiley Periodicals, Inc. Int J Chem Kinet 40: 25–33, 2008     

Experimental and modeling study of ice melting

Differential scanning calorimetry (DSC) is applied to analyse the process of ice melting. Experimental results were compared to those obtained by a numerical simulation in which a conventional enthalpy formulation was applied. The effects of various parameters on the kinetics of transformations and therefore the shape of curves has been analysed and the importance of temperature gradients inside the sample evaluated.     

Acetaldehyde oxidation in the negative temperature coefficient regime: Experimental and modeling results

Acetaldehyde oxidation has been studied in experiments at temperatures of 553 and 713 K carried out in a low pressure, static reactor and in numerical modeling calculations using a detailed chemical kinetic reaction mechanism. The results of the experimental study were used to construct and validate the reaction mechanism, which was then used to examine acetaldehydeoxidation in the negative temperature coefficient regime between 550 and 900 K. This mechanism was also tested against independent measurements of acetaldehyde oxidation carried out by Baldwin, Matchan, and Walker. The overall rate of reaction and the properties of the negative temperature coefficient regime were found to be sensitive to the competition between radical decomposition reactions and the addition of molecular oxygen to acetyl and methyl radicals, including particularly During these experiments, an upper limit to the rate of decomposition ofCH₃O₂H was measured at 553 K. Implications of the results for future kinetic modeling of engine knock are discussed.     

Ethylene pyrolysis and oxidation: A kinetic modeling study

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).