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Primary and secondary reactions of the pyrolysis of C3H3Br and 1,3-butadiene in the SiC tubular microreactor.

Understanding the combustion chemistry of biofuel compounds is of great importance in the intelligent selection of next-generation alternative fuels. Ethylene glycol (C

Cool flame oxidation of hydrocarbon fuels produces substantial intermediates with various levels of chemical reactivity, which can be used for combustion control of advanced engines with low-temper...

Soft photoionization molecular-beam mass spectrometry (PI-MBMS) using synchrotron vacuum ultraviolet (SVUV) light has been significantly developed and applied in various fields in recent decades. Particularly, the tunability of SVUV light enables two-dimensional measurements

The pyrolysis of 1-heptene was studied in a flow reactor using synchrotron vacuum ultraviolet photoionization mass spectrometry at 0.04 and 1 atm and in a jet-stirred reactor using gas chromatography at 1 atm. Flow reactor pyrolysis products, including the allyl radical, cycloalkenes and aromatics, were identified and quantified. Alkenes are found to be the dominant product family, among which ethylene is the most abundant product. A detailed intermediate-to-high temperature model of 1-heptene was developed and validated against the new pyrolysis data in this work, as well as previous data of 1-heptene combustion in literature over a wide range of pressures, temperatures and equivalence ratios. Rate of production analysis and sensitivity analysis were performed to reveal the key pathways in fuel decomposition and product formation. The allylic C C bond dissociation reaction is concluded as the most important pathway in 1-heptene decomposition. Reactions of allyl, propargyl and cyclopentadienyl radicals play important roles in the formation of cycloalkenes and aromatics. Furthermore, comparative pyrolysis experiments of 1-hexene and n-heptane were also performed in the jet-stirred reactor at 1 atm using gas chromatography to explore fuel molecular structure effects on pyrolysis reactivity and product distributions among 1-alkene and n-alkane fuels. The comparison between 1-heptene and 1-hexene pyrolysis demonstrates that similar fuel molecular structure results in the similarities in primary fuel decomposition pathways and pyrolysis reactivity. Ethylene is the most abundant product in both 1-alkene pyrolysis, and the feature in 1-heptene molecular structure leads to enhanced formation of ethylene in its pyrolysis. The abundant formation of ethyl and methyl radicals leads to higher production of 1-pentene and 1-butene in 1-heptene and 1-hexene pyrolysis, respectively. The comparison between 1-heptene and n-heptane pyrolysis reveals that the existence of C C double bond enhances the pyrolysis reactivity of 1-heptene. Different from 1-heptene consumption, n-heptane consumption is dominantly controlled by H abstraction reactions instead of unimolecular decomposition reactions. Propene and 1-butene are prone to be produced in 1-heptene pyrolysis, while 1-hexene has higher mole fractions in n-heptane pyrolysis.

2-Methyl-3-buten-2-ol (MBO232) is a biogenic volatile organic compound (BVOC), and has a large percentage of emission into the atmosphere. The vacuum ultraviolet (VUV) photochemistry of BVOCs is of great importance for atmospheric chemistry. Studies have been carried out on several BVOCs but have not extended to MBO232. In the present report, the photoionization and dissociation processes of MBO232 in the energy range of 8.0-15.0 eV have been studied by tunable VUV synchrotron radiation coupled with a time-of-flight mass spectrometer. By measuring the photoionization spectra, the adiabatic ionization energy (AIE) of MBO232 and the appearance energies (AEs) of the eight identified fragment ions (i.e., C4H7O+, C3H7O+, C5H9+, C3H6O+, CH3CO+, CH3O+, C4H5+, and C3H5+) were determined. High-level quantum chemistry calculations suggest that there are 3 direct channels and 5 indirect channels via transition states and intermediates accountable for these fragments. Among the reaction channels, the direct elimination of CH3 is the most dominant channel and produces the resonance-stabilized radical cation. Most interestingly, our results show that the CH3 selectively migrates towards the cation, which leads to the different indirect channels. The CH3 migration is a rare process in the dissociative photoionization of metal-free organic molecules. We explain the process by molecular orbital calculations and electron localization function analysis and explore the non-conventional dissociation channels via the CH3 roaming mechanism. We further perform kinetics analysis using RRKM theory for the channels of interest. The activation barrier, and rate constants are analyzed for the branching fractions of the products. These results provide important implications for the VUV photochemistry of BVOCs in the atmosphere.

1-butene is an important intermediate in combustion of various hydrocarbon fuels and oxygenated biofuels (e.g., butanol). Understanding its oxidation chemistry can help improve ignition and combustion process in advanced engines and provide better emission control. This work addresses a discrepancy between experiments and simulations in 1-butene oxidation at low temperatures, wherein simulations with AramcoMech 3.0 model show greater fuel reactivity than experiments. To further explore 1-butene low temperature reaction pathways from 550 to 910 K, experiments were conducted in three jet-stirred reactors: two coupled to time-of-flight molecular beam mass spectrometers with synchrotron vacuum ultraviolet radiation as the photoionization source, and one coupled to gas chromatography mass spectrometer. Isomeric structure identification, comprehensive species datasets, and reactor cross examinations are provided by the combination of three experiments. The identified isomer-resolved species provide evidence of various 1-butene low temperature reaction pathways. For example, the identification of propanal confirms the Waddington reaction pathway. The kinetic model over-predicts fuel reactivity in the low temperature regime (550–700 K). Updating the rate coefficients of key reactions in the Waddington pathways, e.g., forward and reverse isomerization of hydroxyl-butyl-peroxide to butoxyl-peroxide and Waddington decomposition of butoxyl-peroxide reduces the discrepancies. The role of rate constant updates in each step of the Waddington pathway is evaluated and discussed to provide directions for future model development.

2,2,3-Trimethylbutane (i.e., triptane) is a potential gasoline octane booster with a research octane number (RON) of 112. Recent studies showed that it can be catalytically produced with high selectivity from methanol (CH3OH) and dimethyl ether (DME), which presents a promising route for utilizing biomass derivatives as transportation fuels. Understanding the ignition properties of triptane at engine relevant conditions is crucial for its further evaluation. In this work, a detailed kinetic model for triptane combustion is developed and validated. The rate rules for the low-temperature oxidation reactions are evaluated based on quantum chemistry calculations from literature, and thermochemical properties of all the species are assessed based on new thermodynamic group values with careful treatment of gauche interactions. In addition, alternative isomerization pathways for peroxy-alkylhydroperoxide species (ȮOQOOH) are incorporated in the model. The model is validated against new ignition delay data from facilities at King Abdullah University of Science and Technology (KAUST): rapid compression machine (RCM) experiments at pressures of 20 and 40 bar, equivalence ratios of 0.5 and 1 and across a temperature range of 620 to 1015 K, and shock tube experiments at 2 and 5 bar, 0.5 and 1 equivalence ratio and over 1000–1400 K. Moreover, the model prediction of various species is compared against species profiles from jet stirred reactor experiments at three equivalence ratios (0.5, 1 and 2) at atmospheric pressure. Finally, triptane is compared with its less branched isomers, n-heptane and 2-methylhexane, to evaluate the effect of branching on fuel reactivity and importance of alternative isomerization pathway.

External electric field and plasma assisted combustion show great potential for combustion enhancement, e.g., emission and ignition control. To understand soot suppression by external electric fields and flame ignition in spark ignition engines, flame ion chemistry needs to be investigated and developed. In this work, comprehensive and systematic investigations of neutral and ion chemistry are conducted in premixed rich methane flames. Cations are measured by quadrupole molecular beam mass spectrometry (MBMS), and neutrals are measured by synchrotron vacuum ultra violet photoionization time of flight MBMS (SVUV-PI-TOF-MBMS). The molecular formula and dominant isomers of various measured cations are identified based on literature survey and quantum chemistry calculations. Experimentally, we found that H3O+ is the dominant cation in slightly rich flame (ϕ=1.5), but C3H3+ is the most significant in very rich flames (ϕ=1.8 and 2.0). An updated ion chemistry model is proposed and used to explain the effects of changing equivalence ratio. To further verify key ion-neutral reaction pathways, measured neutral profiles are compared with cation profiles experimentally. Detailed cation and neutral measurements and numerical simulations by this work help to understand and develop ion chemistry models. Deficiencies in our current understanding of ion chemistry are also highlighted to motivate further research.

International audience; Low temperature oxidation chemistry is crucial in the auto-ignition process of internal combustion engines. The development of laboratory based reactors and diagnostic systems promotes understanding of the low temperature oxidation mechanism. This work develops a variable pressure jet-stirred reactor (VP-JSR) platform working from one to ten bar. Compared to previous high pressure studies which routinely use gas chromatography to analyze low temperature oxidation products, the difference in this work is the possibility of probing intermediates by synchrotron vacuum ultraviolet photoionization mass spectrometry via molecular beam sampling. The setup was validated by repeating n-heptane low temperature oxidation experiments at one and ten bar, respectively. Good agreement was observed between the data in this work and the data in the literature. A much more detailed species pool was probed compared to the literature study, including H2O2, carbonyl acids, alkylhydroperoxides, and keto-hydroperoxides. As a first demonstration of the usefulness of this design, the low temperature oxidation of n-heptane with initial fuel mole fraction of 0.005, residence time of 2 s, and equivalence ratio of 1.0 was studied at one, five, and ten bar. The preliminary results, including reactants, final products, and the initial low temperature oxidation intermediates, are discussed. The VP-JSR system developed in this work is valuable for study of the fuel chemistry from one to ten bar, to develop and examine chemical kinetic models, and to guide the development of the reaction system at even higher pressures, such as those in engine function and supercritical conditions.

To explore the fuel isomeric effect on ether combustion characteristics, pyrolysis, and laminar flame propagation of di-n-propyl ether (DPE) and diisopropyl ether (DIPE) were investigated. A new kinetic model of DIPE was developed based on our recent DPE model [Fuel 298 (2021) 120797]. The pyrolysis experiments were carried out in two jet-stirred reactors at near-atmospheric pressure with good agreement on the measurements using synchrotron vacuum ultraviolet photoionization mass spectrometry and gas chromatography/mass spectrometry. The decomposition profile of DIPE showed a faster trend than that of DPE, which can be attributed to the faster alcohol elimination reaction of DIPE. The dominant roles of alcohol elimination reaction and H-abstraction reactions in fuel consumption explain the production of fuel-specific oxygenated species, i.e. n-propanol and propanal in DPE and i-propanol, acetaldehyde and acetone in DIPE. The laminar burning velocities of DPE and DIPE were also measured in a high-pressure constant-volume cylindrical combustion vessel at the initial temperature of 373 K and pressures of 1–10 atm. It was found that the linear DPE propagated faster than DIPE with the branched structure under all investigated conditions. Rate of production analysis and sensitivity analysis were also performed to elucidate the key radicals and reactions responsible for the remarkable reactivity of isomeric fuels. Fuel structures have a great influence on the distribution of radical pools, resulting in the easy formation of active radicals in DPE flames such as vinyl and ethyl and stable radicals in DIPE flames like methyl and allyl. The successive decomposition reactions of these dominant radicals promote the DPE flame and inhibit the DIPE flame propagation respectively, which explains the higher laminar burning velocities and reactivity of DPE than that of DIPE. Furthermore, the present model was also examined against the literature data, including pyrolysis and oxidation in the jet-stirred reactor and flow reactor.

1- and 2-pentene are components in gasoline and are also used as representative alkene components in gasoline surrogate fuels. Most of the available ignition delay time data in the literature for these fuels are limited to low pressures, high temperatures and highly diluted conditions, which limits the kinetic model development and validation potential of these fuels. Therefore, ignition delay time measurements under engine-like conditions are needed to provide target data to understand their low-temperature fuel chemistry and extend their chemical kinetic validation to lower temperatures and higher pressures. In this study, both a high-pressure shock tube and a rapid compression machine have been employed to measure ignition delay times of 1- and 2-pentene over a wide temperature range (60 0-130 0 K) at equivalence ratios of 0.5, 1.0 and 2.0 in 'air', and at pressures of 15 and 30 atm. At high-temperatures (> 900 K), the experimental ignition delay times show that the fuel reactivities of 1and 2-pentene are very similar at all equivalence ratios and pressures. However, at low temperatures, 1-pentene shows negative temperature coefficient behavior and a higher fuel reactivity compared to 2-pentene. Moreover, carbon monoxide time-histories for both 1- and 2-pentene were measured in a high-pressure shock tube for a stoichiometric mixture at 10 atm and at high temperatures. Furthermore, species versus temperature profiles were measured in a jet-stirred reactor at = 1.0 and 1 atm over a temperature range of 70 0-110 0 K. All of these experimental data have been used to validate the current chemistry mechanism. Starting from a published pentane mechanism, modifications have been made to the 1and 2-pentene sub-mechanisms resulting in overall good predictions. Moreover, flux and sensitivity analyses were performed to highlight the important reactions involved in the oxidation process. (C) 2020 The Authors. Published by Elsevier Inc. on behalf of The Combustion Institute. This is an open access article under the CC BY license. The authors at NUI Galway recognize funding support from Science Foundation Ireland (SFI) via project number 16/SP/3829 and also funding from Computational Chemistry LLC. The work at LLNL was performed under the auspices of the U.S. Department of Energy (DOE) by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344 and was conducted as part of the Co-Optimization of Fuels & Engines (Co-Optima) project sponsored by the DOE Office of Energy Efficiency and Renewable Energy (EERE), Bioenergy Technologies and Vehicle Technologies Offices. The work at KAUST was supported by the KAUST Clean Fuels Consortium (KCFC) via its Office of Sponsored Research and member companies. This work at UCF was conducted as part of the Co-Optimization of Fuels & Engines (Co-Optima) project sponsored by the U.S. Department of Energy (DOE) Office of Energy Efficiency and Renewable Energy (EERE) [grant numbers DE-EE007982, DE-EE007984]. peer-reviewed

Elucidating the formation of combustion intermediates is crucial to validate reaction pathways, develop reaction mechanisms and examine kinetic modeling predictions. While high-temperature pyrolysis and oxidation intermediates of alkanes have been thoroughly studied, comprehensive analysis of cool flame intermediates from alkane autoxidation is lacking and challenging due to the complexity of intermediate species produced. In this work, jet-stirred reactor autoxidation of four C10 alkanes: n-decane, 2-methylnonane, 2,7-dimethyloctane, and n-butylcyclohexane, as model compounds of diesel fuel, was investigated from 500 to 630 K using synchrotron vacuum ultraviolet photoionization molecular beam mass spectrometry (SVUV-PIMS). Around 100 intermediates were detected for each fuel. The classes of molecular structures present during the autoxidation of the representative paraffinic functional groups in transport fuels, i.e., n-alkanes, branched alkanes, and cycloalkanes were established and were found to be similar from the oxidation of various alkanes. A theoretical approach was applied to estimate the photoionization cross sections of the intermediates with the same carbon skeleton as the reactants, e.g., alkene, alkenyl keto, cyclic ether, dione, keto-hydroperoxide, diketo-hydroperoxide, and keto-dihydroperoxide. These species are indicators of the first, second, and third O2 addition reactions for the four C10 hydrocarbons, as well as bimolecular reactions involving keto-hydroperoxides. Chemical kinetic models for the oxidation of these four fuels were examined by comparison against mole fraction of the reactants and final products obtained in additional experiments using gas chromatography analysis, as well as the detailed species pool and mole fractions of aforementioned seven types of intermediates measured by SVUV-PIMS. This works reveals that the models in the literature need to be improved, not only the prediction of the fuel reactivity and final products, but also the reaction network to predict the formation of many previous undetected intermediates.

Comprehensive analysis of the low-temperature oxidation intermediates, including the reactive intermediates and isomers, is crucial to develop the low-temperature oxidation models of the fuels. In this aim, the complementary analysis by different analytic methods is needed. Furthermore, the cross check by different analytic methods increases the fidelity of the experiment data. In this work, we developed a jet-stirred reactor (JSR) system that coupled to the synchrotron vacuum ultraviolet photoionization mass spectrometry (SVUV-PIMS) and gas chromatography (GC) analysis. The JSR was designed to couple the SVUV-PIMS and GC, and the temperature homogeneity and mixing of the JSR was examined by a CFD simulation. The SVUV-PIMS system was developed to have a mass resolution of ca. 5000 at m/z 100. The GC system included a flame ionization detector (FID), thermal conductivity detector (TCD), and a mass spectrometer (MS). This newly developed setup was validated by repeating the oxidation data of n-heptane in the literature. A good agreement was observed between the two datasets. The low-temperature oxidation of n-butane was then studied to show the advantage of this setup, i.e., the simultaneous and comprehensive measurement of the low-temperature oxidation products. Specifically, the SVUV-PIMS enables the separation of the C/H/O composition of the intermediates, the measurement of formaldehyde and the peroxide intermediate, while the GC analysis gives a better separation of the oxygenated isomers and the quantification of the species that the SVUV-PIMS has difficult in quantifying. The experimental method developed in this work is valuable to study the fuel low-temperature oxidation chemistry, to reveal the species pool, and to provide reliable mole fraction data for the validation and development of combustion models.

Furan-based derivatives are promising biomass fuels that may be used directly in internal combustion engines as alternative fuels or as additives to fossil fuels. In this work, the experimental studies of 2-acetylfuran (AF2) pyrolysis were carried out in a jet-stirred reactor in the temperature range of 770 – 1130 K and at the pressure of 760 Torr, using synchrotron vacuum ultraviolet photo-ionization mass spectrometry, coupled with gas chromatography. Key pyrolysis intermediates such as methane, ethylene, acetylene, ketene, vinylacetylene, cyclopentadiene, ethynylketene, 2-methylfuran, furfural, carbon monoxide and isomers such as allene/propyne, furan/vinylketene, benzene/fulvene, etc., were identified and quantified. The potential energy surfaces of AF2 unimolecular decomposition reactions were calculated at CBS-QB3 level. The temperature- and pressure-dependent rate constants of the relevant reactions were calculated by solving the master equation based on Rice-Ramsperger-Kassel-Marcus theory. A detailed pyrolysis kinetics of AF2 was developed based on the previous combustion models of 2-methylfuran and was validated against the current experimental results. Rate of production and sensitivity analysis showed that the main consumption pathways of AF2 pyrolysis under atmospheric pressure are unimolecular decomposition reactions, leading to 2-furyl + acetyl and furoyl + methyl, and hydrogen atom-addition reaction to C(5), leading to 2,3-dihydro-5-acetyl-3-furyl, accounting at 1070 K for 25.1%, 13.2% and 20.7% of AF2 consumption, respectively (the remaining 41.0% are due to minor reaction channels contributing

Hydroperoxyalkylperoxy species are important intermediates that are generated during the autoignition of transport fuels. In combustion, the fate of hydroperoxyalkylperoxy is important for the performance of advanced combustion engines, especially for autoignition. A key fate of the hydroperoxyalkylperoxy is a 1,5 H-shift, for which kinetics data are experimentally unavailable. In the present work, we study 1-hydroperoxypentan-3-yl)dioxidanyl (CH3CH2CH(OO)CH2CH2OOH) as a model compound to clarify the kinetics of 1,5 H-shift of hydroperoxyalkylperoxy species, in particular α-H isomerization and alternative competitive pathways. With a combination of electronic structure calculations, we determine previously missing thermochemical data, and with multipath variational transition state theory (MP-VTST), a multidimensional tunneling (MT) approximation, multiple-structure anharmonicity, and torsional potential anharmonicity, we obtained much more accurate rate constants than the ones that can computed by conventional single-structure harmonic transition state theory (TST) and than the empirically estimated rate constants that are currently used in combustion modeling. The roles of various factors in determining the rates are elucidated. The pressure-dependent rate constants for these competitive reactions are computed using system-specific quantum RRK theory. The calculated temperature range is 298–1500 K, and the pressure range is 0.01–100 atm. The accurate thermodynamic and kinetics data determined in this work are indispensable in the detailed understanding and prediction of ignition properties of hydrocarbons and alternative fuels.

Through the use of tunable vacuum ultraviolet light generated by the DESIRS VUV synchrotron beamline, a jet-stirred reactor was coupled for the first time to an advanced photoionization mass spectrometer based upon a double imaging PhotoElectron PhotoIon COincidence (i2PEPICO) scheme. This new coupling was used to investigate the low-temperature oxidation of n-pentane, a prototype molecule for gasoline or diesel fuels. Experiments were performed under quasi-atmospheric pressure (1.1 bar) with a residence time of 3 s for two equivalence ratios (1/3 and 0.5) with a fuel initial mole fraction of 0.01. The measured time-of-flight mass spectra are in good agreement with those previously obtained with other photoionization mass spectrometers and, like those previous ones, display several m/z peaks for which the related species assignation is ambiguous. This paper shows how the analysis of the coincident mass-tagged Threshold PhotoElectron Spectra (TPES) together with first principle computations, consisting of the determination of the adiabatic ionization energies and the spectra of some products, may assist products’ identification. The results mostly confirm those previously obtained by photoionization mass spectrometry and gas chromatography, but also allow a more accurate estimation of the 1-pentene/2-pentene mole fraction ratio. Our data also indicate a higher formation of acetone and methyl ethyl ketone than what is predicted by current models, as well as the presence of products that were not previously taken into account, such as methoxyacetylene, methyl vinyl ketone or furanone. The formation of three, four and five membered ring cyclic ethers is confirmed along with linear ketones: 2- and 3-pentanone. A significant general trend in indicating higher amounts of ketones than are indicated by gas chromatography is noted. Finally, TPES of alkenylhydroperoxides are also provided for the first time and constrains on the isomers identification are provided. 22;3

Acetaldehyde is an observed emission species and a key intermediate produced during the combustion and low-temperature oxidation of fossil and bio-derived fuels. Investigations into the low-temperature oxidation chemistry of acetaldehyde are essential to develop a better core mechanism and to better understand auto-ignition and cool flame phenomena. Here, the oxidation of acetaldehyde was studied at low-temperatures (528–946 K) in a jet-stirred reactor (JSR) with the corrected residence time of 2.7 s at 700 Torr. This work describes a detailed set of experimental results that capture the negative temperature coefficient (NTC) behavior in the low-temperature oxidation of acetaldehyde. The mole fractions of 28 species were measured as functions of the temperature by employing a vacuum ultra-violet photoionization molecular-beam mass spectrometer. To explain the observed NTC behavior, an updated mechanism was proposed, which well reproduces the concentration profiles of many observed peroxide intermediates. The kinetic analysis based on the updated mechanism reveals that the NTC behavior of acetaldehyde oxidation is caused by the competition between the O2-addition to and the decomposition of the CH3CO radical.

Normal alkanes constitute a significant fraction of transportation fuels, and are the primary drivers of ignition processes in gasoline and diesel fuels. Low temperature ignition of n-alkanes is driven by a complex sequence of oxidation reactions, for which detailed mechanisms are still being developed. The current study explores the dynamics of low-temperature ignition of n-hexane/air mixtures, and identifies chemical pathways that characterize the combustion process. Two chemical kinetic mechanisms were selected as a comparative study in order to better understand the role of specific reaction sequences in ignition dynamics: one mechanism including a new third sequential O 2 addition reaction pathways (recently proposed by Wang et al. 2017), while the other without (Zhang et al. 2015). The analysis is conducted by applying tools generated from the computational singular perturbation (CSP) approach to two distinct ignition phenomena: constant volume and compression ignition. In both cases, the role of the third sequential O 2 addition reactions proves to be significant, although it is found to be much more pronounced in the constant volume cases compared to the HCCI. In particular, in the constant volume ignition case, reactions present in the third sequential O 2 addition reaction pathways (e.g., KDHP → products + OH) contribute significantly to the explosivity of the mixture; when accounted for along with reactions P(OOH) 2 + O 2 → OOP(OOH) 2 and OOP(OOH) 2 → KDHP + OH, they decrease ignition delay time of the mixture by up to 40%. Under HCCI conditions, in the first-stage ignition, the third-O 2 addition reactions contribute to the process, although their role decays with time and becomes negligible at the end of the first stage. The second ignition stage is dominated almost exclusively by hydrogen-related chemistry.

The authors appreciate the funding support from National Key R&D Program of China (2017YFE0123100) and National Natural Science Foundation of China (91841301, U1832171). The authors acknowledge fundings from KAUST Clean Fuels Consortium (KCFC) and its member companies. The authors would like to thank KAUST Supercomputing Laboratory for supporting the quantum chemistry calculations, and Mr. Nitin Lokachari and Ms. Geyuan Yin for sharing the IC8D4 models in their papers. The authors are also grateful to Mr. Jonathan Peterson for checking the English.

This work presents a comprehensive experimental and kinetic modeling study on the combustion of n -propylbenzene. Flow reactor pyrolysis of n -propylbenzene at 0.04, 0.2 and 1 atm and laminar premixed flames of n -propylbenzene at 0.04 atm with equivalence ratios of 0.75 and 1.00 were investigated with synchrotron vacuum ultraviolet photoionization mass spectrometry. Jet stirred reactor (JSR) oxidation of n -propylbenzene at 10 atm with equivalence ratios of 0.5, 1.0, 1.5 and 2.0 was investigated with gas chromatography. A detailed kinetic model for n -propylbenzene combustion with 340 species and 2069 reactions was developed and validated against the data measured in this work. Model analyses such as rate of production analysis and sensitivity analysis were also performed to reveal the key pathways in the consumption of fuel and formation of polycyclic aromatic hydrocarbons (PAHs). The analysis results demonstrate that the benzylic C C bond dissociation reaction is crucial for the decomposition of n -propylbenzene in the pyrolysis and rich flame. Low temperature oxidation reactions play important roles in the high pressure JSR oxidation of n -propylbenzene. In addition, the formation pathways of PAHs are strongly related to the fuel structure, especially for the formation of bicyclic PAHs such as indene and naphthalene. Furthermore, the present model was also validated against previous experimental data of n -propylbenzene combustion under a wide range of conditions, including ignition delay times, laminar flame speeds, extinction strain rates, speciation profiles in atmospheric pressure JSR oxidation, flow reactor oxidation and high pressure shock tube pyrolysis and oxidation.

Bromofluorobenzene(BrFPh) is one of the major volatile atmospheric pollutants. In this paper, using the VUV synchrotron radiation as the excitation source, the photoionization time of flight mass spectra of ortho-, meta-, para-BrFPh moleclues were recorded and the mass spectra illustrated that BrFPh molecule would be ionized into C 6 H 4 B r F + and then dissociate into C 6 H 4 F + and Br atom under the synchrotron radiation. Then the photoionization efficiency (PIE) curves of each parent ions and fragment ions were obtained by plotting the ion intensity versus photon energy. And the photoionization energies of three isomers of BrFPh molecules were determined to be 9.10 eV, 9.16 eV, 8.98 eV. Meanwhile, the photodissociation energies of o-, m-, p- C 6 H 4 B r F + ions were determined to be 3.71 eV, 3.50 eV and 3.63 eV, respectively. Furthermore, the photoionization and photodissociation energies of them were also calculated based on DFT via B3LYP/6–311++G basis set. The theoretical results are in excellent agreement with the experimental values, and could provide important theoretical support for the experimental analysis of the photoionization and dissociative photoionization process of BrFPh molecules.

Alkylated cycloalkanes are vital components in gasoline, aviation, and diesel fuels; however, their combustion chemistry has been less investigated compared to other hydrocarbon classes. In this work, the combustion kinetics of n-propylcyclohexane (n-Pch) was studied across a range of experiments including pressurized flow reactor (PFR), jet stirred reactor (JSR), shock tube (ST), and rapid compression machine (RCM). These experiments cover a wide range of conditions spanning low to intermediate to high temperatures, low to high pressures at lean to rich equivalence ratios. Stable intermediate species were measured in PFR over a temperature range of 550–850 K, pressure of 8.0 bar, equivalence ratio ( φ ) of 0.27, and constant residence time of 120 ms. The JSR was utilized to measure the speciation during oxidation of n-Pch at φ of 0.5–2.0, at atmospheric pressure, and across temperature range of 550–800 K. Ignition delay times (IDTs) for n-Pch were measured in the RCM and ST at temperatures ranging from 650 to 1200 K, at pressures of 20 and 40 bar, at φ = 0.5 , 1.0 . In addition, a comprehensive detailed chemical kinetic model was developed and validated against the measured experimental data. The new kinetic model, coupled with the breadth of data from various experiments, provides an improved understanding of n-Pch combustion.

Control of surface wettability is very important and useful for many industrial applications, and can be realized by controlling surface chemistry and microstructure simultaneously. Here, we present a facile laser-based surface texturing method to achieve switchable wettability control on titanium surface. The experimental results indicate that the laser-treated surfaces became superhydrophilic immediately upon laser texturing. Using alternate low-temperature heat treatment and UV irradiation, the wettability of the laser-treated surface could be efficiently switched between superhydrophilicity and superhydrophobicity for many times. Surface morphology and chemistry analyses confirm that the reversible wettability transition should be attributed to the combined effect of the dual-scale surface structure and controllable surface chemistry. Using the laser-based wettability control method, a water collection device was fabricated and demonstrated by a superhydrophobic-superhydrophilic hybrid surface pattern. The developed method could enable a practical throughput for large-area processing, and endow various industrial applications.

The pyrolysis of 1-hexene was studied in a flow reactor by synchrotron vacuum ultraviolet photoionization mass spectrometry and gas chromatography combined with mass spectrometry at 0.04, 0.2, and 1 atm. Laminar flame speeds of 1-hexene/air mixtures at various pressures (1, 2, 5, and 10 atm) were measured at an initial temperature of 373 K and equivalence ratios from 0.7 to 1.5. A kinetic model of 1-hexene combustion with 122 species and 919 reactions was developed to investigate the key pathways in the decomposition of 1-hexene and the formation and consumption of products, as well as the chemical kinetic effects on the laminar flame propagation. The presence of double bond in 1-hexene molecule leads to the enhanced formation of resonantly stabilized radicals and unsaturated intermediates. The model was also validated against the experimental data of 1-hexene combustion from literature, including ignition delay times and species profiles in jet-stirred reactor oxidation and laminar premixed flames. The extensive validations demonstrate the applicability of the present model over a wide range of conditions, such as low to high pressures, intermediate to high temperatures, and pyrolysis to oxidation circumstances.

Comprehensive low-temperature oxidation mechanisms are needed to accurately predict fuel auto-ignition properties. This paper studies the effects of a previously unconsidered third O 2 addition reaction scheme on the simulated auto-ignition of n -alkanes. We demonstrate that this extended low-temperature oxidation scheme has a minor effect on the simulation of n -pentane ignition; however, its addition significantly improves the prediction of n -hexane auto-ignition under low-temperature rapid compression machine conditions. Additional simulations of n -hexane in a homogeneous charge compression ignition engine show that engine-operating parameters (e.g., intake temperature and combustion phasing) are significantly altered when the third O 2 addition kinetic mechanism is considered. The advanced combustion phasing is initiated by the formation and destruction of additional radical chain-branching intermediates produced in the third O 2 addition process, e.g. keto-dihydroperoxides and/or keto-hydroperoxy cyclic ethers. Our results indicate that third O 2 addition reactions accelerate low-temperature radical chain branching at conditions of relevance to advance engine technologies, and therefore these chemical pathways should also be considered for n -alkanes with 6 or more carbon atoms.

Initiator could accelerate the rate of hydrocarbon pyrolysis and reduce the required material temperatures for a hypersonic aircraft heat exchanger/reactor. Nitroalkanes were proposed as the effective initiator because of the lower C N bond dissociation energy. In order to investigate the initiation mechanism of nitroalkanes on hydrocarbon pyrolysis, the pyrolysis of n -decane, nitromethane and their binary mixture were carried out at 30, 150 and 760 Torr in a flow reactor with synchrotron vacuum ultraviolet photoionization mass spectrometry (SVUV-PIMS). The identified and quantified pyrolysis species include C 1 C 2 alkanes, C 2 C 10 alkenes, C 3 C 6 dialkenes, C 2 C 3 alkynes, nitrogen oxides such as NO and NO 2 , benzene, and radicals including CH 3 , C 3 H 3 , and C 3 H 5 , which shed light on the mechanism of n -decane and nitromethane pyrolysis, as well as the interactions of these two fuels. The experimental results indicate that the addition of nitromethane decreases the initial decomposition temperature of n -decane, and a stronger promotion effect could be obtained as the experimental pressure increases. The distributions of alkanes, alkenes, dialkenes, alkynes and benzene are also influenced by the addition of nitromethane. A detailed kinetic model with 266 species and 1648 reactions was developed and validated against the mole fraction profiles of reactants, major products and important intermediates during the pyrolysis of each fuel and their binary mixture. The satisfactory model prediction to the experimental measurements permits the analysis of the kinetic effect of nitromethane initiation on the pyrolysis of n -decane. So that, the increase of the conversion rate at a lower temperature, the selectivity of decomposition products, and reduction of benzene formation are better understood.

© 2015 The Combustion Institute. Chain-branching reactions represent a general motif in chemistry, encountered in atmospheric chemistry, combustion, polymerization, and photochemistry; the nature and amount of radicals generated by chain-branching are decisive for the reaction progress, its energy signature, and the time towards its completion. In this study, experimental evidence for two new types of chain-branching reactions is presented, based upon detection of highly oxidized multifunctional molecules (HOM) formed during the gas-phase low-temperature oxidation of a branched alkane under conditions relevant to combustion. The oxidation of 2,5-dimethylhexane (DMH) in a jet-stirred reactor (JSR) was studied using synchrotron vacuum ultra-violet photoionization molecular beam mass spectrometry (SVUV-PI-MBMS). Specifically, species with four and five oxygen atoms were probed, having molecular formulas of C8H14O4(e.g., diketo-hydroperoxide/keto-hydroperoxy cyclic ether) and C8H16O5(e.g., keto-dihydroperoxide/dihydroperoxy cyclic ether), respectively. The formation of C8H16O5species involves alternative isomerization of OOQOOH radicals via intramolecular H-atom migration, followed by third O2addition, intramolecular isomerization, and OH release; C8H14O4species are proposed to result from subsequent reactions of C8H16O5species. The mechanistic pathways involving these species are related to those proposed as a source of low-volatility highly oxygenated species in Earth's troposphere. At the higher temperatures relevant to auto-ignition, they can result in a net increase of hydroxyl radical production, so these are additional radical chain-branching pathways for ignition. The results presented herein extend the conceptual basis of reaction mechanisms used to predict the reaction behavior of ignition, and have implications on atmospheric gas-phase chemistry and the oxidative stability of organic substances.