Experimental and kinetic modeling study of oxidation of acetonitrile

Oxidation of acetonitrile has been studied in a flow reactor in the absence and presence of nitric oxide. The experiments were conducted at atmospheric pressure in the temperature range 1150–1450 K, varying the excess air ratio from slightly fuel-lean to very lean. Oxidation of CH₃CN was slow below 1300 K. Nitric oxide, hydrogen cyanide and nitrous oxide were detected as important products. A detailed chemical kinetic model for oxidation of acetonitrile was developed, based on a critical evaluation of data from literature. The rate coefficients for the reactions of CH₃CN and CH₂CN with O₂ were calculated from ab initio theory. Modeling predictions were in satisfactory agreement with experiments. Calculations were sensitive to thermal dissociation of CH₃CN and to the branching fraction for CH₃CN + OH to CH₂CN + H₂O and HOCN + CH₃, respectively. More work is desirable for these steps, as well as for reactions of CH₂CN and HCCN.     

A high temperature and atmospheric pressure experimental and detailed chemical kinetic modelling study of 2-methyl furan oxidation

An experimental ignition delay time study for the promising biofuel 2-methyl furan (2MF) was performed at equivalence ratios of 0.5, 1.0 and 2.0 for mixtures of 1% fuel in argon in the temperature range 1200–1800 K at atmospheric pressure. Laminar burning velocities were determined using the heat-flux method for mixtures of 2MF in air at equivalence ratios of 0.55–1.65, initial temperatures of 298–398 K and atmospheric pressure. A detailed chemical kinetic mechanism consisting of 2059 reactions and 391 species has been constructed to describe the oxidation of 2MF and is used to simulate experiment. Accurate reproduction of the experimental data has been obtained over all conditions with the developed mechanism. Rate of production and sensitivity analyses have been carried out to identify important consumption pathways of the fuel and key kinetic parameters under these conditions. The reactions of hydrogen atom with the fuel are highlighted as important under all experimental conditions studied, with abstraction by the hydrogen atom promoting reactivity and hydrogen atom addition to the furan ring inhibiting reactivity. This work, to the authors knowledge, is the first to combine theoretical and experimental work to describe the oxidation of any of the alkylated furans. The mechanism developed herein to describe 2MF combustion should also function as a sub-mechanism to describe the oxidation of 2,5-dimethyl furan whilst also providing key insights into the oxidation of this similar biofuel candidate.     

A high-temperature study of 2-pentanone oxidation: experiment and kinetic modeling

Small methyl ketones are known to have high octane numbers, impressive knock resistance, and show low emissions of soot, NO_x, and unburnt hydrocarbons. However, previous studies have focused on the analysis of smaller ketones and 3-pentanone, while the asymmetric 2-pentanone (methyl propyl ketone) has not gained much attention before. Considering ketones as possible fuels or additives, it is of particular importance to fully understand the combustion kinetics and the effect of the functional carbonyl group. Due to the higher energy density in a C₅-ketone compared to the potential biofuel 2-butanone, the flame structure and the mole fraction profiles of species formed in 2-pentanone combustion are of high interest, especially to evaluate harmful species formations. In this study, a laminar premixed low-pressure (p?=?40 mbar) fuel-rich (??=?1.6) flat flame of 2-pentanone has been analyzed by vacuum-ultraviolet photoionization molecular-beam mass-spectrometry (VUV-PI-MBMS) enabling isomer separation. Quantitative mole fraction profiles of 47 species were obtained and compared to a model consisting of an existing base mechanism and a newly developed high-temperature sub-mechanism for 2-pentanone. High-temperature reactions for 2-pentanone were adapted in analogy to 2-butanone and n-pentane, and the thermochemistry for 2-pentanone and the respective fuel radicals was derived by ab initio calculations. Good agreement was found between experiment and simulation for the first decomposition products, supporting the initial branching reactions of the 2-pentanone sub-mechanism. Also, species indicating low-temperature chemistry in the preheating zone of the flame have been observed. The present measurements of a 2-pentanone flame provide useful validation targets for further kinetic model development.     

Experimental and kinetic modeling study of C2H4 oxidation at high pressure

A detailed chemical kinetic model for oxidation of C₂H₄ in the intermediate temperature range and high pressure has been developed and validated experimentally. New ab initio calculations and RRKM analysis of the important C₂H₃ + O₂ 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 CH₂O and HCO, is the dominant product. The experiments, involving C₂H₄/O₂ mixtures diluted in N₂, 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 C₂H₄ are more complex than those prevailing at higher temperatures and lower pressures. The major differences are the importance of the hydroxyethyl (CH₂CH₂OH) and 2-hydroperoxyethyl (CH₂CH₂OOH) radicals, formed from addition of OH and HO₂ to C₂H₄, and vinyl peroxide, formed from C₂H₃ + O₂. Hydroxyethyl is oxidized through the peroxide HOCH₂CH₂OO (lean conditions) or through ethenol (low O₂ concentration), while 2-hydroperoxyethyl is converted through oxirane.     

Experimental and modelling study of gasoline surrogate mixtures oxidation in jet stirred reactor and shock tube

The oxidation of several mixtures of surrogate for gasoline was studied using a jet stirred reactor and a shock tube. One representative of each classes constituting gasoline was selected: iso-octane, toluene, 1-hexene and ethyl tert-butyl ether (ETBE). The experiments were carried out in the 800-1880 K temperature range, for two different initial pressures (0.2 and 1 MPa), with an initial fuel molar fraction of 0.001. The equivalence ratio varied from 0.5 to 1.5. Each hydrocarbon sub-mechanism was validated using shock tube data. The full mechanism describing the surrogate fuel oxidation is constituted of the sub-mechanisms for each fuel components and by adding interaction reactions between different hydrocarbon fragments. Good agreement between the experimental results and the computations was observed under JSR and shock tube conditions.     

Experimental and semi-detailed kinetic modeling study of decalin oxidation and pyrolysis over a wide range of conditions

Decalin is the simplest polycyclic alkane (polynaphtenic hydrocarbon) found in liquid fuels (jet fuels, Diesel). In order to better understand the combustion characteristics of decalin, this study provides new experimental data for its oxidation in a jet-stirred reactor. For the first time, stable species concentration profiles were measured in a jet-stirred reactor at a constant mean residence time of 0.1 s and 0.5 s at respectively 1 and 10 atm, over a range of equivalence ratios (? = 0.5–1.5) and temperatures (750–1350 K). The oxidation of decalin under these experimental conditions was modeled using a semi-detailed chemical kinetic reaction mechanism (11,000 reactions involving 360 species) derived from a previously proposed scheme for the ignition of the same fuel in a shock-tube. The proposed mechanism that includes both low- and high-temperature chemistry shows reasonably good agreement with the present experimental data set. It can also represent well decalin pyrolysis and oxidation data available in the literature. Reaction path analyses and sensitivity analyses were conducted to interpret the results.     

A wide-range experimental and kinetic modeling study of the pyrolysis and oxidation of 2-butyne

To reduce particulate emissions leading to a cleaner environment, it is important to understand how polycyclic-aromatic hydrocarbons (PAHs) and their precursors are formed during combustion. 2-butyne can decompose to propargyl and allyl radicals. These radicals can produce benzene and other PAHs, leading to the formation of soot. In the present study, pyrolysis, oxidation, and laminar flame speed experiments were performed for 2-butyne. The pyrolysis experiments were conducted in a single-pulse shock tube at 2 bar in the temperature range 1000 – 1500 K. Ignition delay times for 2-butyne/‘air’ mixtures were measured in the pressures range 1 – 50 bar, over the temperature range 660 – 1630 K, at equivalence ratios of 0.5, 1.0, and 2.0 using rapid compression machines and shock tubes. Moreover, laminar flame speed (LFS) experiments were performed at ambient temperature, at p = 1 – 3 atm, over an equivalence ratio range of 0.6 – 1.8. A new, detailed chemical kinetic model for 2-butyne has been developed and widely validated against the data measured in this study and those available in the literature. The significant reactions for 2-butyne pyrolysis, ignition, and oxidation are identified and discussed using flux and sensitivity analyses.     

Experimental and modeling study of H2S formation and evolution in air staged combustion of pulverized coal

High-concentration H₂S formed in the reduction zone of pulverized coal air-staged combustion can result into the high temperature corrosion of water wall tube of boiler, so it is of great importance to accurately predict H₂S concentration for the safe operation of boilers and burners. H₂S formation and evolution depends on two steps: the sulfur release from coal conversion and gas-phase reactions of sulfur species. In this study, the sulfur release characteristics from the pyrolysis of 17 coals, including 5 lignite, 9 bituminous coals and 3 anthracites, are investigated in a drop tube furnace (DTF). Sulfur release model is developed to describe the relationship between sulfur release and coal types. A global gas-phase reaction mechanism of sulfur species composed of ten reactions is used to calculate and predict the formation and evolution of H₂S, COS and SO₂ in the reduction zone of pulverized coal air-staged combustion. A wide range of air-staged combustion experiments of 17 coals are conducted in the DTF at different temperatures and stoichiometric ratios to validate the developed model. The results show that the prediction errors of sulfur species, including SO₂, H₂S and COS, are within ± 30%, which indicates that the developed prediction model of sulfur species is of great assistance for CFD modeling of actual engineering application.     

Experimental and kinetic modeling studies of low- to moderate-temperature oxidation of 2-furfuryl alcohol in a jet-stirred reactor

2-Furfuryl alcohol, a promising platform chemical, and alternative fuels or additives, is produced from the hydrogenation of furfural. However, the low- to moderate-temperature oxidation study of 2-furfuryl alcohol is scarce up to now. The present study first performed the oxidation experiments in a jet-stirred reactor at the equivalence ratios of 0.5, 1.0, and 2.0. The oxidation species were identified and measured by the synchrotron vacuum ultraviolet photoionization mass spectrometry. No negative-temperature-coefficient behavior was observed. A detailed kinetic model was developed to better understand the consumption of 2-furfuryl alcohol and the formation of oxidation products. The present model can well reproduce the experimental results. Based on the rate of production analysis, H-abstraction reactions on hydroxymethyl group forming hydroxyl(2-furyl)methyl radical are the dominant pathways. Besides, the formation and consumption of main products, such as furfural, furan, acrolein, acetaldehyde, etc., are also discussed. Fuel radicals control the formation of furfural. Furan has multiple formation sources, such as the H-addition reactions on 2-furfuryl alcohol, furfural, and 2-hydroxyfuran. Acrolein is produced by the H-addition reaction on 2-hydroxyfuran and OH-addition reactions on furan. Also, the present work compares and discusses peak concentration for major oxidation products of 2-furfuryl alcohol and 2-methyl furan under the same simulated condition. 2-Furfuryl alcohol oxidation produces a higher concentration of furfural, furan, and acrolein than that of 2-methyl furan. OH on hydroxymethyl group promotes the H-abstraction reactions on the side chain and inhibits the OH-addition reaction on the furan ring.     

Experimental and detailed kinetic modeling study of the high pressure oxidation of methanol sensitized by nitric oxide and nitrogen dioxide

The perturbation of the combustion by NO_x is important in several practical systems (recent NO_x-reduction strategies, combustion with exhaust-gas recirculation in diesel and HCCI engines and for mild combustion). New experimental results were obtained for the oxidation of methanol in absence and in presence of NO or NO₂ in a fused silica jet-stirred reactor operating at 10 atm, over the temperature range 700-1100 K. Probe sampling followed by on-line FTIR analyses and off-line GC-TCD/FID analyses permitted to measure the concentration profiles of the reactants, stable intermediates and the final products. A detailed chemical kinetic modeling of the present experiments was performed. An overall good agreement between the present data and this modeling was obtained. The oxidation of methanol is significantly sensitized by NO₂, whereas the effect of NO is more limited. According to the proposed model, the mutual sensitization of the oxidation of methanol and NO proceeds through the NO to NO₂ conversion by HO₂. The increased production of OH resulting from the oxidation of NO by HO₂ promotes the oxidation of the fuel. A simplified reaction scheme can be proposed for the NO-seeded oxidation of methanol: NO + HO₂ ⇒ NO₂ + OH followed by OH + CH₃OH ⇒ H₂O + CH₂OH and CH₃O. The enhanced oxidation of methanol by addition of NO₂ is also due to additional OH production through: NO₂ + HO₂ ⇒ HONO + O₂, NO₂ + H ⇒ NO + OH and HONO ⇒ NO + OH followed by OH + CH₃OH ⇒ CH₂OH and CH₃O. The further reactions CH₂OH + O₂ ⇒ CH₂O + HO₂; CH₃O ⇒ CH₂O + H; CH₂O + OH ⇒ HCO; HCO + O₂ ⇒ HO₂ and H + O₂ ⇒ HO₂ complete the sequence whether NO or NO₂ is added.     

Theoretical study of molecular properties of low-lying electronic excited states of H2O and H2S

Geometries, excitation energies, dipole moments and dipole polarisability tensor components of the ground and four lowest excited states ³ B ₁, ¹ B ₁, ³ A ₂, ¹ A ₂ of the H₂O and H₂S molecules were calculated at the CASSCF, CASPT2, CCSD and CCSD(T) level of approximation. Vertical excitation and equilibrium transition energies of these states, having the Rydberg character, are reported too. Properties of both molecules in the ground and in low lying excited states are compared and discussed from the point of view of their molecular electronic structure. Upon excitation we observe dramatic changes of dipole moments and polarisabilities with respect to the ground state. We stress the change of the polarity of H₂O in all excited states accompanied by the enhancement of the dipole polarisability by an order of magnitude. Large, even if less pronounced, are changes of electric properties of H₂S in its excited states. Dipole moments and dipole polarisabilities of ³ B ₁, ¹ B ₁ states of H₂S and H₂O behave quite analogously in comparison to their respective ground state. The general pattern of properties for both molecules in their ³ A ₂ and ¹ A ₂ excited states is more different due to a pronounced participation of the sulphur d-orbitals in these states of the H₂S molecule.     

Hydrogen-nitrous oxide delay times: Shock tube experimental study and kinetic modelling

Hydrogen-nitrous oxide mixtures have been studied for decades. In addition to their fundamental interest, they might play an important role in semi-conductor industry safety. Indeed, in silane-nitrous oxide mixtures, widely used in this industry, the silane molecule readily decomposes into molecular hydrogen which can react violently with nitrous oxide. Despite numerous shock tube studies on H₂-N₂O delay times, the pressure effect has never been addressed. The present work aims at studying this effect and at developing a detailed kinetic mechanism able to accurately reproduce experimental delay time data. Delay times of H₂-N₂O-Ar mixtures have been measured behind reflected shock waves in the 1300-2000 K temperature range and at a pressure around 300 kPa. Mixtures equivalence ratios ranged between 0.5 and 2, and the dilution was 98 and 99 mol% Ar. The present results and those from a previous study carried out in our institute show, first that, in the studied conditions, the equivalence ratio has no influence on delay times, and second, that the pressure increase drastically reduces the delay times. A kinetic model has been constructed from previously published mechanisms and tested against the present data with a mean error of 29%. Moreover, other delay time data from the literature for H₂-O₂-Ar, NH₃-Ar and H₂-N₂O-Ar mixtures are also correctly reproduced as well as macroscopic parameters such as reduced activation energies.     

Experimental and kinetic modelling studies of flammability limits of partially dissociated NH3 and air mixtures

This paper presents a set of experimental and kinetic modelling studies of the flammability limits of partially dissociated NH₃ in air at 295 K and 1 atm. The experiments were carried out using a Hartmann bomb apparatus. The kinetic modelling was performed using Ansys Chemkin-Pro with opposed-flow premixed flame model employing three detailed reaction mechanisms, namely, the Mathieu and Petersen, Otomo et al., and Okafor et al. mechanisms. The degree of NH₃ dissociation was varied from 0 to 25% (0 to 20%v/v H₂ in the fuel mixture with a fixed H₂/N₂ ratio of 3). It was found that the lower (LFL) and upper (UFL) flammability limits of pure NH₃ in air were 15.0%v/v and 30.0%v/v, respectively, consistent with the literature data. The flammability limits of the mixture widened significantly with increasing the degree of NH₃ dissociation. At 25% NH₃ dissociation, LFL decreased to 10.1%v/v and UFL increased to 36.6%v/v. All tested mechanisms were able to predict the extinction characteristics exhibited by the lean and rich mixtures of partially dissociated NH₃ in air with non-unity Lewis numbers. While all three mechanisms predict well LFL, the Otomo et al. mechanism showed the best agreement with the experimental data of UFL. The rate of production of radicals, sensitivity, and reaction path analyses were performed to identify the key elementary reactions and radicals during combustion of partially dissociated NH₃. The production of key radicals including OH, H, O, and NH₂ was enhanced in the presence of H₂ and thus the conversion of NH to NO and then NO to N₂ near LFL and the conversion of NH₂ and NO to N₂ near UFL leading to wider flammability limits.     

H2S和H2S+的振动光谱和电子能谱计算

本文基于MOLPRO软件包使用从头算方法计算了星际分子H₂S及其阳离子H₂S⁺的势能面及光电子能谱.首先,在(U)CCSD/cc-pVQZ理论水平下获取了H₂S沿法线坐标展开的势能面,势能面直观描述了不同振动模式耦合对分子能量变化的影响,S-H键的非对称伸缩振动和面内弯曲振动共同作用使得系统势能变化范围明显变大.振动多组态相互作用方法被用来计算非谐振动频率和振动光谱,计算结果显示,倍频和组合频之间出现了强烈的费米共振,使得相应波段处的红外强度显著增强.最后,使用拉曼波函数和收缩不变Krylov子空间方法首次计算了H₂SΧ¹A₁→H₂S⁺ X²B₁的光电子能谱.此项研究有助于进一步理解星际分子的内部结构,并为实验研究及星际观测提供参考.     

An experimental and kinetic modeling study on the oxidation of 1,3-dioxolane

The modern catalytic or enzymatic advances allow the production of novel biofuel. Among them, 1,3-dioxolane can be produced from formaldehyde and ethylene glycol, both can be obtained from biomass. In this study, the oxidation of 1,3-dioxolane is studied at stoichiometric conditions. The ignition delay times of 1,3-dioxolane/O₂/inert mixtures were measured in a shock tube and in a rapid compression machine at pressures of 20 to 40 bar and temperatures ranging from 630 to 1300 K. The pressure profiles recorded in the rapid compression machine show a first stage of ignition enlightening the influence of the low temperature chemistry of combustion. Furthermore, mole fraction profiles of the stable intermediates produced during the oxidation of 1,3-dioxolane were measured in a jet-stirred reactor at 10 bar. Following these observations, a detailed kinetic model was developed with reaction rate coefficients and thermochemical data calculated by theoretical calculations or estimated by analogies to suitable molecules. In order to get an insight into the most important reaction pathways brute force sensitivity analysis and reaction pathway analysis were performed with the proposed model and discussed. It became clear that in the fuel-in-air case for the alkylhydroperoxide of 1,3-dioxolane the ring opening beta-scission pathway is favored against the further alkane-like second addition to molecular oxygen, which leads to a limited negative temperature coefficient.     

Experimental and kinetic modeling study of sooting atmospheric-pressure cyclohexane flame

Experimental data and modelling results of the main products and intermediates from a fuel-rich sooting premixed cyclohexane flame were presented in this work. Model predictions well agree with experimental data both in sooting and non-sooting flames. Major and minor species are properly predicted, together with the soot yield. The initial benzene peak was demonstrated to be due to the fast dehydrogenation reactions of the cycloalkane, which gives rise to cyclohexene and cyclohexadiene both via molecular and radical pathways. Once formed cyclohexadiene quickly forms benzene whereas in the postflame zone, benzene comes from the recombination and addition reactions of small radicals, with C₃H₃ + C₃H₃ playing the most important role in these conditions. An earlier soot inception was detected in the cyclohexane flame with respect to a n-hexane flame and this feature is not reproduced by the model that foresees soot formation significant only in the second part of the flame. The model insensitivity of soot to the reactant hydrocarbon was also observed comparing the predictions of three flames of cyclohexane, 1-hexene and n-hexane with the same temperature profile. A sensitivity analysis revealed that soot primarily comes from the HACA mechanism for the three flames, acetylene being the key species in the nucleation. Experimental data on soot inception seem to indicate the importance of the early formation of benzene, that depends on the fuel structure. It is thus important to further investigate the role of benzene and aromatics in order to explain this discrepancy.     

基于第一性原理计算H_2S、CO_2、CH_4在Fe-MoS_2上的吸附性能

在高含硫气藏开发中,伴随着CH_4的采出,H_2S和CO_2也不可避免的被采出.这两种气体会产生管道腐蚀和气体中毒等诸多不利影响.为了解决这一现实需要,从研究较为广泛的MoS_2材料入手,考虑了其掺杂结构中的吸附性能的变化,相关计算原理基于密度泛函数理论.主要计算了一种吸附式掺杂过渡金属原子Fe在MoS_2上的结构,同时也计算了H_2S,CO_2,CH_4气体在其表面的吸附能,电荷转移,电子密度差等相关参数.结果表明,CH_4对这种材料表现出不敏感的特性,而CO_2、H_2S均表现出吸附的性质,预测这种材料可能作为一种可使用的吸附材料,或是开发作为一种新型的气体预警材料.     

Methane/propane oxidation at high pressures: Experimental and detailed chemical kinetic modeling

Shock tube experiments and chemical kinetic modeling were performed to further understand the ignition and oxidation kinetics of various methane-propane fuel blends at gas turbine pressures. Ignition delay times were obtained behind reflected shock waves for fuel mixtures consisting of CH₄/C₃H₈ in ratios ranging from 90/10% to 60/40%. Equivalence ratios varied from lean (? = 0.5), through stoichiometric to rich (? = 3.0) at test pressures from 5.3 to 31.4 atm. These pressures and mixtures, in conjunction with test temperatures as low as 1042 K, cover a critical range of conditions relevant to practical turbines where few, if any, CH₄/C₃H₈ prior data existed. A methane/propane oxidation mechanism was prepared to simulate the experimental results. It was found that the reactions involving CH₃O˙, CH₃O˙₂, and ?H₃ + O₂/HO˙₂ chemistry were very important in reproducing the correct kinetic behavior.