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Pyrolysis of 1,2,4-trimethylcyclohexane (T124MCH) at 30 and 760 Torr has been investigated by using VUV-synchrotron photoionization molecular-beam mass spectrometry. In general, the ambient pressure leads to peak-shaped profiles of light hydrocarbons, while the monotonically increasing curves are observed for light hydrocarbons and aromatics in pyrolysis of T124MCH at low pressure. A detailed mechanism involving 530 species and 3160 reactions developed by the authors previously was used for the simulation of T124MCH with reasonable predictions. The consumption of T124MCH followed similar patterns at both pressures, namely the H-abstractions on the first, secondary, and tertiary carbon atoms are the main consumption reactions of T124MCH. The isomerization reactions transform the C9H17 radicals to branch-chain hydrocarbons, which are the precursors of light hydrocarbons such as ethane and propene. Sensitivity analysis indicates that the CH3 consumption reactions are the most significant promoting reactions at both pressures. Isomerization reactions of T124MCH tend to play significant inhibiting effect on T124MCH pyrolysis. Compared to T124MCH oxidation, T124MCH pyrolysis tends to produce large quantities of benzene and toluene. These results will improve the understanding of the combustion and soot formation of T124MCH as a potential aviation surrogate fuel.

Pyrolysis study of iso-propylbenzene (IPB) at 30 and 760 torr was carried out by using synchrotron photoionization and molecular beam mass spectrometry techniques. 0.5%IPB was diluted by helium and heated to 798–1148 K in a flow tube. Styrene was the most abundant aromatic intermediate at both pressures. Several polycyclic aromatics were only observed at 760 torr, such as 2-ethenyl-1, 4-dimethyl-benzene, fluorene, anthracene, phenanthrene, 2-methyl-anthracene and pyrene, while fulvene, 1, 3-cyclohexadiene, and 5-ethenylidene-1, 3-cyclopentadiene were only detected at 30 torr. A detail mechanism involving 306 species and 1990 reactions was developed by updating ipso-addition and unimolecular dissociation reactions of IPB as well as reactions related to styrene, indene and naphthalene. The mechanism could predict the pyrolysis of IPB and production of other intermediates well. Rate-of-production analysis shows that the formations of 2-phenethyl, 1-iso-phenylpropyl and 2-iso-phenylpropyl radicals are the main consumption reactions of IPB independent of pressure. Sensitivity analysis indicates that the unimolecular dissociation of IPB forming 2-phenethyl radical is the most significant promoting reaction at both pressures. H-abstraction reaction forming 1-iso-phenylpropyl radical tends to play a significant inhibiting effect on IPB consumption at 30 torr, while the most inhibiting reaction is self-combination of methyl radicals at 760 torr. Compared to n-propylbenzene experiments reported by Liu et al. (Combustion and Flame, 191 (2018) 53–65) and Yuan et al. (Combustion and Flame,186 (2017) 178–192.), IPB tends to produce larger quantities of benzene, styrene and indene under pyrolysis and oxidation conditions. These results will improve the understanding of the combustion and soot formation of IPB as a potential aviation surrogate fuel.

A comparison study of the oxidation of n-propylbenzene (NPB), iso-propylbenzene (IPB), 1,3,5-trimethylbenzene (T135MB), 1,2,4-trimethylbenzene (T124MB) in a same jet-stirred reactor was performed to find a most suitable transport fuel as a surrogate component. The experimental results show that IPB with the weakest C H bond tends to be the most active fuel among the four C9H12 fuels, while T135MB is the slowest. Ten common intermediates detected in all experiments and eight characteristic intermediates were comprehensively compared, including hydrocarbons, aromatics and oxygenated species. NPB and IPB tend to produce more hydrocarbons and benzene, while T124MB and T135MB generate more toluene and acrolein. Based on the previous studies, an universal mechanism was presented by involving the four sub-mechanisms with good prediction on the measured results. The rate-of-production analysis shows that H-abstraction on the methyl or propyl is the dominant consumption pathway of C9H12 fuels, while C9H11 radicals maintains bigger differences than the initial reactions. Sensitivity analysis shows that CH3 is the key intermediate in the consumption of propylbenzenes, and OH plays similar role in the oxidation of trimethylbenzenes. Moreover, the production pathways of the aldehydes and PAHs in the oxidation were also discussed to understand the pollutant formations. Benzyl and styrene are believed to be the main precursors of aldehydes and PAHs, respectively. In general, these results provide better understanding of the oxidation and combustion of C9H12 fuels as potential surrogate fuel constituents for kerosene and diesel. Furthermore, the comprehensive experimental and modeling studies of C9H12 fuels could also offer the guidance function for the surrogate component selection.

The pyrolysis and oxidation of nitromethane (NM) were studied in a plug flow reactor over the temperature range of 735–1476 K at 5 Torr and in a jet-stirred reactor over the temperature range of 600–875 K at atmospheric pressure, respectively. Mole fraction profiles of major products and intermediates were identified with tunable synchrotron vacuum ultraviolet photoionization and molecular-beam mass spectrometry. The current study represents the first comprehensive characterization of NM conversion under these conditions. The experimental results were compared to predictions with a detailed chemical kinetic model involving 364 species and 2389 reactions. The rate constants for significant dissociation reactions CH3NO2 = CH3 + NO2 and CH3NO2 = HCNO + H2O were calculated by the RRKM/Master Equation method using Variflex program in this work. The model provided an overall reasonable agreement with the measured data, but for pyrolysis conditions future work is required to improve predictions of some intermediates. Rate-of-production analysis indicates that the primary decomposition pathways of NM are different for pyrolysis and oxidation due to the effects of C N bond fission and roaming mediated isomerization. From the sensitivity analysis, the two pathways mentioned above have promoting effects on NM consumption for all the studied conditions, while the reaction of CH3+NO2 CH3O+NO with inhibiting effect at Φ=2.0 shows promoting effects for Φ=0.4 and pyrolysis. This work extends the experimental database and helps to improve the understanding of low temperature chemistry of NM.

The low-temperature oxidation (LTO) of pyridine was studied in a jet-stirred reactor over the temperature range of 700–1000 K at atmospheric pressure and equivalence ratio of 2.0. Mole fraction profiles of the reaction products were obtained based on molecular beam mass spectrometry and tunable vacuum ultraviolet synchrotron photoionization techniques. Hydrogen peroxide, methanamine, acetylenamine, ethenamine, acetaldimine, ethylamine, allyamine, and methylformamide were newly identified compared with previous studies of pyridine flame and pyrolysis. HCN was found to be the dominant N-containing species of pyridine LTO. Pyrrole, acrylonitrile, acetonitrile, and ammonia were also found at the same level of N2O and NO. Based on the new measurements and updated rate constants of several reactions including the H-abstractions of pyridine as well as the oxidation of ortho-pyridyl using density functional theory calculations, a new pyridine LTO kinetic model consisting of 588 species and 3516 reactions was developed with a reasonable agreement with the experimental results. In general, the predictions of the predominant species have been improved compared with the existing model. Rate-of-production analysis indicates that pyridine mainly consumes via C5H5N→C5H4N→C5H4NO2→HCN+CO+ C H 2 CH C ˙ O , and C5H5N→C5H5NO→C2H2+HCN+CH2CO. Sensitivity analysis shows that C5H4N+O2=>C5H4NO2, and C5H5N+OH C5H4N+H2O have significant promoting effect on pyridine consumption, while the reverse of C5H4N+HO2 C5H4NO+OH has strong inhibiting effect. The results will enrich the understanding of pyridine low-temperature oxidation mechanism, which can be applied to the fields of coal pre-treatment, staged combustion and mild combustion.

This work describes the experimental and modeling study of low temperature oxidation of 1,3,5-trimethylbenzene (T135MB) in a jet-stirred reactor over the temperature range of 700–1100 K at atmospheric pressure under fuel-lean and stoichiometric conditions. 9 C0 C5 hydrocarbons, 6 oxygenated products and 6 aromatic compounds were identified and quantified using GC and GC-MS. A detailed kinetic based on T135MB model of Dievart et al. was proposed to simulate the low-temperature experimental results in the present work. Rate constants of T135MB decomposition and metatheses reactions were calculated with CBS-QB3 method implemented in Gaussian 09. The performance of proposed mechanism in reproducing the experimental data is reasonably good. Reaction flux analysis shows that dominant consumption channels for T135MB oxidation are H-abstraction reactions to form 3,5-dimethylbenzyl radicals, while reactions with O/OH radicals to generate 1,3,5-trimethylphenoxyl/1,3,5-trimethylphenyl and ipso-addition to form m-xylene play minor roles. Sensitivity analysis reveals that H-abstraction from side methyl groups of T135MB by OH radical is the most inhibiting reaction oxidation at Φ = 1.0, while it is a promoting reaction at Φ = 0.4. Moreover, current model were validated against experimental results on T135MB oxidation in flow reactor from Dievart et al. as well as global combustion property ignition delay times from Rao et al. and Dievart et al. with reasonable predictions.

The low temperature oxidation of neat 1,3,5-trimethylbenzene (T135MB) and n-decane/T135MB mixture as a surrogate for JP-8 has been investigated in a jet-stirred reactor over the temperature range of 500–1100 K at atmospheric pressure under fuel-rich condition with residence time from 2.33 to 1.06 s. Mole fraction profiles of 29 intermediates including light hydrocarbons, oxygenated and aromatic compounds were identified by gas chromatographic techniques. In general, the concentrations of intermediates tend to increase progressively with temperature from 925 K in neat T135MB oxidation, while these species exhibit bimodal distributions from 550 K in the oxidation of n-decane/T135MB mixture (surrogate). By considering the calculated rate constants of T135MB and analogous coupling reactions between T135MB and n-decane, a detailed kinetic mechanism involving 910 species and 5329 reactions was established with a reasonable agreement with the experimental results. The low temperature chemistry of T135MB and surrogate was analyzed including the NTC behavior below 800 K. The oxidation process of T135MB is occurring mainly by H-abstraction with OH radical and subsequent reactions. The difference is that in the NTC region H-abstraction by OH radicals is the major consumption pathway for T135MB in the surrogate. But for neat T135MB, the dominant channels change to the H-abstractions by H-atoms, OH and CH3 radicals. Addition of n-decane can promote the oxidation of T135MB by providing OH radicals in the low temperature oxidation of surrogate fuel. Moreover, the model was also validated against the experimental data on n-decane and JP-8 combustion, including species profiles in low temperature jet-stirred reactor oxidation and high temperature flow reactor pyrolysis as well as ignition delay times. These extended results yielded overall satisfactory agreement, and will benefit for further application of practical JP-8 fuels, particularly for their combustion properties at wide temperature range.