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The pyrolysis of 2,5-dimethylfuran (DMF) in a flow reactor was investigated at various pressures (30, 150 and 760 Torr) by synchrotron vacuum ultraviolet photoionization mass spectrometry (SVUV-PIMS). Dozens of pyrolysis products, especially a series of radicals and aromatics, were identified from the measurement of photoionization efficiency spectra; and their mole fraction profiles were measured at 780–1470 K. Phenol, 1,3-cyclopentadiene, 2-methylfuran, vinylacetylene and 1,3-butadiene were observed with high concentrations in the decomposition of DMF. The pressure-dependent rate constants of the major unimolecular decomposition reactions of DMF were theoretically calculated, and was adopted in the pyrolysis model of DMF with 285 species and 1173 reactions developed in the present work. The model was validated against the species profiles measured in both the present work and the previous pyrolysis studies of DMF. Based on the rate of production and sensitivity analyses, main pathways in the decomposition of DMF and the growth of aromatics were determined. The unimolecular decomposition to produce CH 3 CHCCH and acetyl radicals, H-atom abstraction to produce 5-methyl-2-furanylmethyl radical, ipso substitution by H-atom to produce 2-methylfuran and H-atom attack to produce 1,3-butadiene and acetyl radical were concluded to dominate the primary decomposition of DMF. Further decomposition of 5-methyl-2-furanylmethyl radical leads to great production of phenol and 1,3-cyclopentadiene which can be readily converted to precursors of large aromatics such as cyclopentadienyl radical, phenyl radical and benzene. As a result, the formation of aromatics in the pyrolysis of DMF is promoted compared with the pyrolysis of cyclohexane and methylcyclohexane under very close conditions. This observation implies the potentially high sooting tendency of DMF, and emphasizes the necessity to investigate the sooting behavior and soot formation mechanism in DMF combustion for the potential application of DMF as an alternative engine fuel. [ABSTRACT FROM AUTHOR]

Abstract: The pyrolysis of cyclohexane at low pressure (40mbar) was studied in a plug flow reactor from 950 to 1520K by synchrotron VUV photoionization mass spectrometry. More than 30 species were identified by measurement of photoionization efficiency (PIE) spectra, including some radicals like methyl, propargyl, allyl and cyclopentadienyl radicals, and stable products (e.g., 1-hexene, benzene and some aromatics). Among all the products, 1-hexene is formed at the lowest temperature, indicating that the isomerization of cyclohexane to 1-hexene is the dominant initial decomposition channel under the condition of our experiment. We built a kinetic model including 148 species and 557 reactions to simulate the experimental results. The model satisfactorily reproduced the mole fraction profiles of most pyrolysis products. The rate of production (ROP) analysis at 1360 and 1520K shows that cyclohexane is consumed mainly through two reaction sequences: cyclohexane→1-hexene→allyl radical+ n-propyl radical, and cyclohexane→cyclohexyl radical→hex-5-en-1-yl radical that further decomposes to 1,3-butadiene via hex-1-en-3-yl and but-3-en-1-yl radicals. Besides the stepwise dehydrogenation of cyclohexane, C3+C3 channels, i.e. C3H3 +C3H3 and C3H3 +aC3H5 also have important contribution to benzene formation. The simulation reveals that C3H3 +C3H3 =phenyl+H reaction is the key step for other aromatics formation, i.e. toluene, phenylacetylene, styrene, ethylbenzene and indene in this work. [Copyright &y& Elsevier]

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. [ABSTRACT FROM AUTHOR]

To uncover the fundamental chemistry of branched alkyl radical reaction with O 2 , especially the second oxidation process (O 2 + QOOH), iso-butyl is chosen as a combustion archetype and reactions on the potential energy surfaces of C 4 H 9 O 2 and C 4 H 9 O 4 are investigated by using quantum chemical calculations coupled with RRKM/master-equation method. In the present study we calculate the thermodynamics properties, the rate constants and branching ratios for major reaction pathways in a wide temperature range of 298−2400 K and pressure range of 0.01−10 atm. Our study indicates that the treatment of estimating the fate of OOQOOH in the second oxidation process by analogy with similar reaction type and molecular size for the fate of RO 2 in the first oxidation process could cause significant deviations. The accurate calculations conform that the rate constants for the second O 2 barrierless addition (QOOH + O 2) is half of the first O 2 barrierless addition (R + O 2). Morever, the accurate thermodynamics and kinetics data determined in the present work are indispensable for the detailed understanding and prediction of ignition properties of larger hydrocarbons. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Isoprene (2-methyl-1,3-butadiene) is not only the main component in gasoline and a potential fuel additive, but also is considered an important precursor of polycyclic aromatic hydrocarbons. To better understand the isoprene pyrolysis process, the pyrolysis experiments of isoprene in a flow reactor were performed at p = 30 Torr for T = 1056 – 1446 K, and p = 760 Torr for T = 850 – 1231 K. More than twenty pyrolysis species, especially radicals (methyl, propargyl, and but‑2‑yne-1-yl), isomers (allene/propyne, buta-1,2,3-triene/vinylacetylene, 1,3-butadiene/1-butyne), and aromatics (benzene, toluene, phenylacetylene, styrene, indene, and naphthalene), were identified and their mole fraction profiles were measured using synchrotron vacuum ultraviolet photoionization mass spectrometry. The potential energy surfaces of the unimolecular decomposition, H/CH 3 -abstraction, and H/CH 3 -addition reactions of isoprene were also calculated using quantum chemical calculations at the CBS-QB3 level. Based on the experimental and theoretical results, a detailed kinetic model was developed and validated against the pyrolysis experimental dataset of isoprene from this work and Grajales-González et al. H-addition reactions on the double bond and H-abstraction reactions by H/CH 3 radicals controlled the consumption of isoprene. The C–H bond dissociation reaction on the –CH 3 was the dominant unimolecular reaction in comparison with the isomerization reactions. Abundant aromatics were produced in isoprene pyrolysis, especially at atmospheric pressure, which is ascribed to the high-level concentration of C(2)–C(4) hydrocarbons formation, such as acetylene, ethylene, allene, propyne, 1,3-butadiene, etc. [ABSTRACT FROM AUTHOR]

In this work, pyrolysis experiments of ethyl valerate were performed in a flow reactor over 705–1051 K at low and atmospheric pressures and in a jet-stirred reactor over 633–1013 K at near-atmospheric pressure. Products were measured with synchrotron vacuum ultraviolet photoionization mass spectrometry in the flow reactor pyrolysis and gas chromatography in the jet-stirred reactor pyrolysis. Valeric acid and ethylene were observed as the most abundant pyrolysis products in both experiments. Laminar burning velocities of ethyl valerate/air mixtures were also measured in a high-pressure constant-volume cylindrical combustion vessel at the initial temperature of 443 K and initial pressures of 1–10 atm. A kinetic model of ethyl valerate combustion incorporated with recent theoretical progress was developed to predict the new experimental data in this work, as well as the speciation data under flame conditions and laminar burning velocities at different initial temperatures and pressures in literature. Experimental observations and modeling analyses both confirm the significant role of the intramolecular elimination reaction of ethyl valerate producing valeric acid and ethylene. In particular, this reaction has exclusive significance in decomposition of ethyl valerate under pyrolysis conditions, indicating pyrolysis experiments can provide crucial constraints for its rate constant. Subsequent decomposition reactions of valeric acid at higher temperatures enrich the intermediate pool, especially radicals, and can continue producing ethylene to make its mole fraction keep growing under the investigated temperature ranges in the jet-stirred reactor pyrolysis. Under the flame propagation conditions, C 0 C 1 reactions have the highest sensitivity coefficients to the flame propagation, while ethylene- and vinyl-involved reactions also play important roles due to the abundant production of ethylene. [ABSTRACT FROM AUTHOR]

The pyrolysis of 2-ethylfuran (EF2) in a flow reactor was studied by using synchrotron vacuum ultraviolet photoionization mass spectrometry at 846 – 1319 K and at 30 and 760 Torr. Over 20 pyrolysis products were detected and measured. A detailed kinetic model was constructed by extending the reported comprehensive 2,5-dimethylfuran model to describe the pyrolysis of EF2 and validated against the current experimental results, including methyl, 2-furylmethyl, propargyl, acetylene, ethylene, propene, ketene, 2-vinylfuran, furan/vinylketene and benzene, etc. Rate of production analysis and sensitivity analysis indicate that the main reaction pathways of EF2 pyrolysis are H-abstraction reactions forming 1-(2-furyl)ethyl and 2-(2-furyl)ethyl, unimolecular decomposition reactions forming 2-furylmethyl, and H-addition reactions forming furan and vinylketene. The corresponding products, 2-vinylfuran, 2-furylmethyl and vinylketene, etc., are indicated to be the most key products in EF2 pyrolysis. Comparisons of the formation of aromatic hydrocarbons in the pyrolysis of EF2, 2-methylfuran and 2,5-dimethylfuran show that EF2 had a lower tendency to produce aromatic soot precursors. [ABSTRACT FROM AUTHOR]

N-methyl pyrrole (NMP) is an important nitrogenous heterocyclic compound in bio-oils produced from biomass conversion. NMP can be used as surrogate model compound to clarify the combustion chemistry of nitrogenous fuels and NO X formation mechanism. The low- to moderate-temperature oxidation experiments of NMP are carried out in atmospheric pressure jet-stirred reactor for 0.5% NMP/oxygen/Argon mixtures at different equivalence ratios (0.5, 1.0, and 2.0) over the temperature range of 760 – 1030 K. More than twenty species, including reactants, nitrogen-containing species, and oxygenated products, are measured using synchrotron vacuum ultraviolet photoionization mass spectrometry (SVUV-PIMS). A detailed and comprehensive kinetic model for NMP oxidation is developed for the first time based on the pyrrole oxidation model developed by Pelucchi et al. and Chen et al.. Simulated results show that the present model can reasonably reproduce the experimental results. Rate of production analysis indicates that the H-abstraction reactions on the methyl group dominate in NMP oxidation at all equivalence ratios. NMP oxidation produces C4 and C5 nitrogen-containing compounds including pyridine and pyrrole. These species are found to be products of the primary reactions of NMP, and their formation pathways can be explained satisfactorily by the present model. The present work provides a basis to further understand the oxidation characteristics of nitrogen-containing heterocyclic fuels. [ABSTRACT FROM AUTHOR]

The rate constants for H-initiated reactions of 2-furfuryl alcohol (2FFOH) were calculated for the first time by a high-level quantum chemical method combined with the Rice–Ramsperger–Kassel–Marcus (RRKM) theory/Master equation method. A detailed potential energy surface was constructed by the CCSD(T)/CBS//M06–2X/def2-TZVP method, involving H-abstraction, initial H-addition, adduct-subsequent pathways and interconnected conversion pathways. The H-addition reaction on the β -carbon and δ -carbon sites to form bimolecular products 2-methylene-2,3-dihydrofuran plus OH and 2-methylene-2,5-dihydrofuran plus OH were found to be the major product channels at high temperatures. No significant pressure dependence is observed for the total rate constants of 2FFOH + H. However, the overall kinetics behavior does not reflect the site characteristics, i.e., the site-specific rate constants for each reaction channel show different temperature and pressure dependences. The total rate constants via the H-addition mechanism are higher by factors of 3.3–10 than those via H-abstraction channels under all studied conditions. The present updated kinetic model obtained by applying these new calculated rate constants can better predict 2FFOH decomposition, especially at 30 Torr, and it can also lead to good predictions of the speciation profiles (e.g., vinyl ketene) during 2FFOH pyrolysis. The data calculated in the present work can provide valuable information for the development of combustion models of furan-based biofuels. [ABSTRACT FROM AUTHOR]

The combustion of tert-butanol was studied experimentally in this work, including flow reactor pyrolysis at 30–760 Torr, laminar flat premixed flame at 30 Torr, coflow methane/tert-butanol diffusion flame at atmospheric pressure, and laminar flame speed at 1–10 atm. Synchrotron vacuum ultraviolet photoionization mass spectrometry (SVUV-PIMS) was applied in the investigation of pyrolysis and flame, and the schlieren technique was used in the measurement of laminar flame speed. A detailed kinetic model consisting of 209 species and 1486 reactions was developed in this work, which can predict the decomposition of tert-butanol and the formation of aromatics over wide temperature and pressure ranges. Kinetic analysis illustrates that the unimolecular decomposition of tert-butanol is the most important and sensitive reaction class in different combustion modes, which readily produce the most important aromatic precursors: tert-butanol → iso-butene → 2-methylallyl → allene → propargyl. As a result, the production of benzene, phenyl radical, and benzyl radical are all enhanced in the combustion of tert-butanol compared to those of other butanol isomers. The self-combination of propargyl and the combination of propargyl with other resonantly stabilized radicals are the key steps of aromatics formation in the combustion of tert-butanol. [ABSTRACT FROM AUTHOR]

2-Furfuryl alcohol, derived from non-edible biomass, is the significant component of bio-oil in the pyrolysis of lignocellulose biomass and a potential alternative fuel or fuel additive. To better optimize the pyrolysis model of lignocellulose to improve the properties of pyrolysis bio-oil and further understand the combustion characteristics of 2-furfuryl alcohol, the pyrolysis experiments were performed in a flow reactor at 30 Torr for T = 1006 – 1339 K and 760 Torr for T = 850 – 1131 K, and in a jet-stirred reactor at 760 Torr for T = 750 – 1050 K. The pyrolysis products, including radicals (methyl, propargyl, allyl, and cyclopentadienyl), isomers (furfural/2-ethyl furan, furan/vinyl ketene, and allene/propyne), and aromatics (benzene, toluene, indene, etc.) were identified and measured using synchrotron vacuum ultraviolet photoionization mass spectrometry. A comprehensive kinetic model for 2-furfuryl alcohol pyrolysis was developed and was validated against the experimental data in the present and previous work. Rate of production analysis indicated that the C–O bond dissociation reaction, H-abstraction reactions on the hydroxymethyl group, and the H-addition reactions on the furan-ring controlled the consumption of 2-furfuryl alcohol and the formation of primary pyrolysis products like 2-methyl furan, 2-ethyl furan, furfural, and furan. In addition, the OH-addition reaction on the furan-ring had a certain contribution to the consumption of 2-furfuryl alcohol, while the contribution of H-shift reactions was negligible. The present work systematically compared the effects of methyl, ethyl, and hydroxymethyl groups on the decomposition of furanic fuels and the formation of major products. The results showed that the substituent groups can reduce the decomposition temperature of the fuels, especially the ethyl and hydroxymethyl groups. The alkyl substituent group can promote the formation of small hydrocarbons, of which the mole fraction increased with the length of the carbon chain increasing. The hydroxymethyl group facilitated the formation of oxygenated products. [ABSTRACT FROM AUTHOR]

Abstract: i-Butanol (iC4H9OH) pyrolysis has been studied in a flow reactor with synchrotron vacuum ultraviolet photoionization mass spectrometry combined with molecular-beam sampling technique. The pyrolysis species were identified and their mole fractions were determined. Three pressures of 30, 150 and 760Torr were selected to study the pressure effect of i-butanol chemistry. A detailed kinetic model consisting of 186 species and 1294 reactions was developed to simulate i-butanol high temperature chemistry. To enhance the accuracy, the model was further validated by the species profiles in shock tube pyrolysis, laminar premixed flames, oxidation data from jet-stirred reactor, ignition delay times, and flame speeds. Good agreement between the predicted and measured results was obtained. [Copyright &y& Elsevier]

Biomass fuel, as a kind of alternative fuel, offers the possibility of a higher sustainability of the energy system. Furanic fuels that are proposed as next-generation biomass-derived fuels have become one of the targets of recent researches. Here the studies on the low-temperature oxidation of 2-ethylfuran (EF2) in a jet-stirred reactor were performed at atmospheric pressure, at temperature range of 600–900 K and at three equivalence ratios of 0.5, 1.0 and 2.0, respectively. Over 20 oxidation products were detected and measured by using synchrotron vacuum ultraviolet photoionization mass spectrometry, including hydrocarbons, such as methane, ethylene, acetylene, et al., and oxygenated species, such as formaldehyde, ketene, acetaldehyde, 2-methylfuran and 2-vinylfuran, especially the isomers (furan/vinyl ketene) et al. A detailed low-temperature oxidation kinetic model with 723 species and 3300 reactions based on the reported models and theoretical calculations was developed to demonstrate the experimental results in this work. Rate of production analysis shows that, in the low-temperature oxidation of EF2, the consumption of EF2 is dominated by hydrogen atom-abstraction to produce 1-(2-furyl)ethyl radical and by hydroxyl radical-addition onto C(2) of EF2 to produce 2,3-dihydro-2-hyroxyl-2-ethyl-3-furanyl radical at 50% EF2 consumption. The subsequent dominant consumption pathway of 1-(2-furyl)ethyl radical reacting with hydroperoxyl radical will generate 1-(2-furyl)ethyloxyl radical or 2,5-dihydro-5-ethyliden-2-furanyloxyl radical, while 2,3-dihydro-2-hyroxyl-2-ethyl-3-furanyl radical will subsequently go through β -scission to produce carbon monoxide + acetylene + formyl radical eventually. Sensitivity analysis indicates that reactions related to these four radicals, i.e., hydroxyl, 1-(2-furyl)ethyl, 2,5-dihydro-5-ethyliden-2-furanyloxyl and 2,3-dihydro-2-hyroxyl-2-ethyl-3-furanyl, are critical in the consumption of EF2. Hydroxyl radical is mainly produced by the decomposition of hydroperoxide at the equivalence ratio of 0.5 and 1.0, while at the equivalence ratio of 2.0, reactions between 1-(2-furyl)ethyl radical and hydroperoxyl radical, as well as that between methyl radical and hydroperoxyl radical, become more important. [ABSTRACT FROM AUTHOR]

Abstract: Methylcyclohexane is the simplest alkylated cyclohexane, and has been broadly used as the representative cycloalkane component in fuel surrogates. Understanding its combustion chemistry is crucial for developing kinetic models of larger cycloalkanes and practical fuels. In this work, the synchrotron vacuum ultraviolet photoionization mass spectrometry combined with molecular-beam sampling was used to investigate the species formed during the pyrolysis of methylcyclohexane and in premixed flame of methylcyclohexane. A number of pyrolysis and flame intermediates were identified and quantified, especially including radicals (e.g. CH3, C3H3, C3H5 and C5H5) and cyclic C6- and C7-intermediates (benzene, 1,3-cyclohexadiene, cyclohexene, toluene, C7H10 and C7H12, etc.). In particular, the observation of cyclic C6- and C7-intermediates provides important experimental evidence to clarify the special formation channels of toluene and benzene which were observed with high concentrations in both pyrolysis and flame of methylcyclohexane. Furthermore, the rate constants of H-abstraction of methylcyclohexane via H attack, and the isomerization and decomposition of the formed cyclic C7H13 radicals were calculated in this work. A kinetic model of methylcyclohexane combustion with 249 species and 1570 reactions was developed including a new sub-mechanism of MCH. The rate of production and sensitivity analysis were carried out to elucidate methylcyclohexane consumption, and toluene and benzene formation under various pyrolytic and flame conditions. Furthermore, the present kinetic model was also validated by experimental data from literatures on speciation in premixed flames, ignition delays and laminar flame speeds. [Copyright &y& Elsevier]

Abstract: Methyl propanoate (MP) pyrolysis in a laminar flow reactor was studied at low pressure (30Torr) within the temperature range from 1000 to 1500K. About 30 products were detected and identified in the pyrolysis process using the photoionization mass spectrometry, including H2, CO, CO2, CH3OH, CH2O, CH2CO, C1 to C4 hydrocarbons and radicals (such as CH3, C2H5 and C3H3). Their mole fraction profiles versus temperature were also measured. For the unimolecular dissociation reactions, the rate constants were calculated by high precision theoretical calculations. Based on the theoretical calculations and measured mole fraction profiles of pyrolysis species, a kinetic model of MP pyrolysis containing 98 species and 493 reactions was developed. The model simulates the primary decomposition process well with the calculated rate constants. According to the rate of production analysis, the decomposition pathways of MP and the formation channels of both oxygenated and hydrocarbon products were discussed. It is concluded that the main decomposition pathway is MP→CH2COOCH3 →CH3CO+CH2O→CO. [Copyright &y& Elsevier]

Abstract: 2-Butanol (sC4H9OH) pyrolysis has been studied in a flow reactor with the synchrotron vacuum ultraviolet photoionization mass spectrometry combined with the molecular-beam sampling technique. The pyrolysis species were identified and their mole fractions were determined. Four pressures of 5, 30, 150 and 760Torr were selected to study the pressure dependence of 2-butanol pyrolysis chemistry. The temperature- and pressure-dependent rate constants of unimolecular reactions of 2-butanol were calculated with the RRKM/Master Equation method. With the help of theoretical calculations, a detailed kinetic model consisting of 160 species and 1038 reactions was developed to simulate the 2-butanol pyrolysis. It is concluded that the mole fractions of pyrolysis species are very sensitive to the 2-butanol unimolecular reaction rates. To enhance the accuracy, the model is further validated by the species profiles in shock tube pyrolysis, a rich laminar premixed flame, oxidation data from jet-stirred reactor, ignition delay times, and laminar flame speed. Good agreements between the predicted and measured results were obtained. [Copyright &y& Elsevier]

Abstract: The low-temperature oxidation of n-heptane, one of the reference species for the octane rating of gasoline, was investigated using a jet-stirred reactor and two methods of analysis: gas chromatography and synchrotron vacuum ultraviolet photoionization mass spectrometry (SVUV-PIMS) with direct sampling through a molecular jet. The second method allowed the identification of products, such as molecules with hydroperoxy functions, that are not stable enough to be detected using gas chromatography. Mole fractions of the reactants and reaction products were measured as a function of temperature (500–1100K), at a residence time of 2s, at a pressure of 800Torr (1.06bar) and under stoichiometric conditions. The fuel was diluted in an inert gas (fuel inlet mole fraction of 0.005). Attention was paid to the formation of reaction products involved in the low-temperature oxidation of n-heptane, such as olefins, cyclic ethers, aldehydes, ketones, species with two carbonyl groups (diones), and ketohydroperoxides. Diones and ketohydroperoxides are important intermediates in the low-temperature oxidation of n-alkanes, but their formation have rarely been reported. Significant amounts of organic acids (acetic and propanoic acids) were also observed at low temperatures. The comparison of experimental data and profiles computed using an automatically generated detailed kinetic model is satisfactory overall. A route for the formation of acetic and propanoic acids was proposed. Quantum calculations were performed to refine the consumption routes of ketohydroperoxides toward diones. [Copyright &y& Elsevier]

Abstract: Pyrolysis of three butene isomers (C4H8) including 1-butene (1-C4H8), 2-butene (2-C4H8) and i-butene (iC4H8) were studied from 900 to 1900K at low pressure. Synchrotron vacuum ultraviolet (VUV) photoionization mass spectrometry with molecular-beam sampling technique was used for isomeric identification of products and intermediates and also for concentration measurement. Based on the experimental results, a kinetic model consisting of 76 species and 232 reactions was developed to simulate mole fractions of species. The mole fraction profiles of pyrolysis species predicted by the model are in good agreement with the experimental measurements. The decomposition pathways of C4H8 are illustrated according to the reaction flux analysis. Our analysis demonstrates that reaction sequences 1-C4H8 →aC3H5 →aC3H4 →pC3H4 →C2H2, 2-C4H8 →saxC4H7 →1,3-C4H6 →C2H3 →C2H2 and iC4H8 → iC4H7 →aC3H4 →pC3H4 →C2H2 are the major decomposition pathways of 1-butene, 2-butene and i-butene, respectively. [Copyright &y& Elsevier]

2-Methylfuran (MF), a promising biofuel, produced from non-edible biomass, is desirable as an alternative fuel or fuel additive to internal combustion engines. For a better understanding of the ignition process in engines, the low-temperature oxidation experiments of MF at the temperature range of 600 – 925 K and atmospheric pressure with different equivalence ratios (0.5, 1.0, and 2.0), were performed in a jet-stirred reactor. Synchrotron vacuum ultraviolet photoionization mass spectrometry was used to identify and measure the intermediates and products in the oxidation process, especially for the isomers (furfural/2-ethylfuran and furan/vinyl ketene), species with identical mass-to-charge ratio (methanol/oxygen and aldehyde/carbon dioxide), and the other oxygenated and hydrocarbon products. The typical negative-temperature-coefficient behavior was not observed in the low-temperature oxidation of MF. The dominant consumption pathways of MF in low-temperature oxidation are the hydroxyl radical/hydrogen atom-addition reactions on the ring and hydrogen atom-abstraction reactions on the side methyl group by hydroxyl radical/hydroperoxyl radical/hydrogen atom, while the contribution of unimolecular decomposition reactions is almost negligible. 2-Furylmethyl radical is a key intermediate in the low-temperature oxidation of MF. Furfural and 2-ethylfuran, as the subsequent products from 2-furylmethyl low-temperature oxidation, were identified as the early-stage products. Besides, the important chemistry of other important species, especially acrolein and methyl vinyl ketone, were also discussed at different equivalence ratios. [ABSTRACT FROM AUTHOR]