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Co-firing ammonia (NH 3) and hydrogen (H 2) or H 2 -rich fuel and partially cracking NH 3 are promising non-carbon combustion techniques for gas turbines and marine engines, raising a growing need to understand the interactions of H 2 and nitric oxide (NO) as well as the non-hydrocarbon nitrogen oxides (NO X) reduction mechanism under flame conditions. In this work, the outwardly propagating spherical flame method was used to investigate the laminar flame propagation of H 2 /NO and H 2 /NO/nitrogen (N 2) mixtures at initial pressure (P u) of 2 atm, initial temperature (T u) of 298 K and equivalence ratios of 0.2-1.4. The laminar burning velocities (LBVs) of H 2 /NO mixtures are generally 5-10 times lower than those of H 2 /air mixtures, while the dilution of N 2 can dramatically inhibit the laminar flame propagation. A kinetic model of H 2 /NO combustion was constructed and validated against the new data in this work and other types of experimental data in literature. The modeling analyses reveal that NO+H=N+OH becomes the most important chain-branching reaction in H 2 /NO reaction system, while the LBV data of H 2 /NO mixtures in this work can provide highly sensitive validation targets for the kinetics in H 2 and NO interactions. Furthermore, the NO reduction to N 2 mainly proceeds through NO+N=N 2 +O under various H 2 /NO ratios, and NO+O=N+O 2 is found to have a significant contribution to NO reduction under NO-rich conditions. [ABSTRACT FROM AUTHOR]

This work reports an investigation on laminar premixed flames of tetralin at 30 Torr and equivalence ratios of 0.7 and 1.7. Measurements of the chemical structure including identification and mole fraction measurements of free radicals, isomers, and polycyclic aromatic hydrocarbons (PAHs) were performed using synchrotron vacuum ultraviolet photoionization mass spectrometry (SVUV‐PIMS). A kinetic model with 296 species and 1 577 reactions was developed and validated against the flame chemical structure data measured in this work. Modeling analysis reveals the key reaction pathways in tetralin decomposition and PAHs formation. The H‐atom abstraction reactions by H, O, and OH are found to control the consumption of tetralin in the lean flame, while those by H play the dominant role in the rich flame. Indene and naphthalene have very high concentration levels in the rich tetralin flame due to the existence of direct formation pathways from the decomposition of tetralin. The two bicyclic PAHs and their radicals play significant roles in the PAHs growth process of tetralin combustion, which results in the high sooting tendency of tetralin compared to those of alkylbenzenes with smaller or same carbon atom numbers. [ABSTRACT FROM AUTHOR]

In order to better understand the low-temperature oxidation chemistry of alkenes, 1-butene and i -butene oxidation experiments triggered by dimethyl ether (DME) were conducted in a jet-stirred reactor at 790 Torr, 500–725 K and the equivalence ratio of 0.35. Low-temperature oxidation intermediates involved in alcoholic radical chemistry and allylic radical chemistry were detected by using synchrotron vacuum ultraviolet photoionization mass spectrometry (SVUV-PIMS). To better interpret the experimental data, a kinetic model was proposed based on our low-temperature oxidation model of DME and comprehensive oxidation models of 1-butene and i -butene in literature. Based on present experimental results and modeling analysis, alcoholic radical chemistry initiated by OH addition is mainly responsible for the low-temperature chain propagation of butenes, since the Waddington mechanism plays a dominant role compared with the chain-branching pathways through the second O 2 addition. Allylic radical+HO 2 reactions producing alkenyl hydroperoxides and fuel+O 2 serve as the major chain-branching and chain-termination pathways, respectively, and they are competitive in the negative temperature coefficient (NTC) region. In contrast, chain-branching pathways originating from allylic radical+O 2 and alkyl-like radical+O 2 reactions have little contribution to the OH formation. Comparison with the simulation results of butane/DME mixtures demonstrates that butenes can largely inhibit the reactivity of DME at low temperatures due to its reduced low-temperature chain-branching process. However, in the NTC region, butenes may not be good OH absorbents since the allylic radicals can convert HO 2 to OH and consequently enhance the oxidation reactivity. [ABSTRACT FROM AUTHOR]

This work reports an experimental and kinetic modeling investigation on the flow reactor pyrolysis of iso -butylbenzene and tert -butylbenzene at 0.04 and 1 atm. Pyrolysis products were detected and identified using synchrotron vacuum ultraviolet photoionization mass spectrometry, and their mole fractions versus heating temperature were measured. High-pressure-limit and pressure-dependent rate constants of unimolecular decomposition reactions of iso -butylbenzene were calculated in this work using the same method as the theoretical calculation investigation on similar reactions of n -butylbenzene, sec -butylbenzene and tert -butylbenzene reported by Belisario-Lara et al. [ J. Phys. Chem. A , 122 (2018) 3980–4001]. Furthermore, a pyrolysis model of four butylbenzene isomers was developed from our previous models of n -butylbenzene and sec -butylbenzene and validated by the present experimental data. Modeling analysis was performed to reveal key pathways in fuel decomposition and polycyclic aromatic hydrocarbon (PAH) formation of iso -butylbenzene and tert -butylbenzene. The dominant decomposition reactions of iso -butylbenzene and tert -butylbenzene under pyrolysis conditions are benzylic C C bond dissociation reactions, while the major products in pyrolysis process are produced by β - scission reactions of primary radical products. Fuel-specific pathways are found to strongly affect the formation of PAHs, especially for indene, naphthalene and phenanthrene. Fuel isomeric effects on the pyrolysis of four butylbenzene isomers were also analyzed with special concerns on the fuel decomposition and PAH formation processes. Different sidechain structures result in different distributions of major products, while different formation pathways and concentrations of precursors lead to different formation tendency of typical PAHs. [ABSTRACT FROM AUTHOR]

In this work, low temperature (low-T) oxidation of 1-heptene was investigated in a jet-stirred reactor (JSR) over the temperatures of 450–800 K, 770 Torr and equivalence ratios of 0.5–2.0. The intermediates were identified and quantified using synchrotron vacuum ultraviolet photoionization mass spectrometry (SVUV-PIMS) and gas chromatography combined with mass spectrometry (GC–MS). The SVUV-PIMS experiment combined with quantum chemistry calculation of ionization energy enables the identification of fuel-specific intermediates, including C 7 alkenylperoxy radical and hydroperoxides, such as diolefinic-hydroperoxide, alkenylhydroperoxide, alkenyl-ketohydroperoxide and cyclic ether hydroperoxide. Among them, alkenylperoxy radical, diolefinic-hydroperoxide and cyclic ether hydroperoxide have not been detected in alkene oxidation before. In order to accurately identify and quantify other fuel-specific intermediates such as aldehyde and cyclic ether isomers, the GC–MS experiment was conducted under the same conditions as the SVUV-PIMS experiment. On the other hand, a detailed low-T oxidation model of 1-heptene was developed, which can reasonably capture the fuel oxidation rate and negative temperature coefficient behaviors observed in this work. The present model can not only interpret the formation of different kinds of hydroperoxides and predict their temperature windows, but also capture the formation of 2-heptenal, hexanal and heptanal, and branched tetrahydrofurans, which are derived from the H-abstraction by OH, OH addition and H addition reactions of 1-heptene, respectively, revealing that the competition between these reactions can be well characterized. [ABSTRACT FROM AUTHOR]

Abstract The kinetics of propanal oxidation was studied in a jet-stirred reactor (JSR) at atmospheric pressure. The investigated temperature range is from 450 to 800 K at two different equivalence ratios (0.35 and 4.0). Thanks to the synchrotron vacuum ultraviolet photoionization mass spectrometry (SVUV-PIMS), critical intermediates were identified, including methylperoxy, methyl hydroperoxide, ethylperoxy, ethyl hydroperoxide, α-lactone, β-propiolactone and ketohydroperoxides. A kinetic model for propanal oxidation was also developed and validated against the present experimental results, as well as those available from the literature. Main chain-branching pathways under the investigated conditions were analyzed based on present experimental data and kinetic model. The O 2 addition reaction to the propanoyl radical and subsequent oxidation reactions play an important role in determining the oxidation rate of propanal under fuel-lean conditions, especially in the low-temperature oxidation region. Under fuel-rich conditions, the decomposition of the propanoyl radical is predominant and C 2 H 5 relevant reactions consequently determine the kinetics of oxidation of propanal. [ABSTRACT FROM AUTHOR]

Two sets of experiments were performed to unravel the high-temperature pyrolysis of tricyclo[5.2.1.02,6] decane (JP-10) exploiting high-temperature reactors over a temperature range of 1100 K to 1600 K, Advanced Light Source (ALS), and 927 K to 1083 K, National Synchrotron Radiation Laboratory (NSRL), with residence times of a few tens of microseconds (ALS) to typically 144 ms (NSRL). The products were identified in situ in supersonic molecular beams via single photon vacuum ultraviolet (VUV) photoionization coupled with mass spectroscopic detection in a reflectron time-of-flight mass spectrometer (ReTOF). These studies were designed to probe the initial (ALS) and also higher order reaction products (NSRL) formed in the decomposition of JP-10 – including radicals and thermally labile closed-shell species. Altogether 43 products were detected and quantified including C1–C4 alkenes, dienes, C3–C4 cumulenes, alkynes, eneynes, diynes, cycloalkenes, cyclo-dienes, aromatic molecules, and most importantly, radicals such as ethyl, allyl, and methyl produced at shorter residence times. At longer residence times, the predominant fragments were molecular hydrogen (H2), ethylene (C2H4), propene (C3H6), cyclopentadiene (C5H6), cyclopentene (C5H8), fulvene (C6H6), and benzene (C6H6). Accompanied by electronic structure calculations, the initial JP-10 decomposition via C–H bond cleavages resulting in the formation of the initial six C10H15 radicals was found to explain the formation of all products detected in both sets of experiments. These radicals are not stable under the experimental conditions and further decompose via C–C bond β-scission processes. These pathways result in ring opening in the initial tricyclic carbon skeletons of JP-10. Intermediates accessed after the first β-scission can further isomerize or dissociate. Complex PAH products in the NRLS experiment (naphthalene, acenaphthylene, biphenyl) are likely formed via molecular growth reactions at elevated residence times. [ABSTRACT FROM AUTHOR]