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We performed systematic ab initio calculations for the pyrolysis of phenyl formate (PF), the simplest aromatic ester, to establish the potential energy surfaces (PESs), thermodynamics and reaction kinetics. Reaction pathways considered in this work include direct bond fission and intramolecular H-shift, as well as subsequent radical decomposition and ipso-addition by H, O and OH radicals. The energies of reactants, transition states and products were determined at the ROCBS-QB3//M062X/cc-pVTZ level of theory. The standard enthalpy of formation of each species was determined using the atomization method, showing a good agreement with the literature results. For the PF unimolecular decomposition, the intramolecular H-shift reactions to produce phenol + CO and 2,4-cyclohexadienone + CO are the dominant decomposition pathways. Among the decomposition reactions of PF radicals, the isomerization and β -scission channels to form phenoxy + CO and C 6 H 4 OH + CO are the dominant pathways. Additionally, for the ipso-addition reactions, PF + H/O → HCOO + C 6 H 6 /C 6 H 5 O and PF + OH → HCOOH + C 6 H 5 O are the major pathways. Multi-well and multi-channel phenomenological rate constants were determined using the Rice–Ramsperger–Kassel–Marcus/master equation (RRKM/ME) method at 500−2000 K and the pressure range of 0.01 atm to the high-pressure limit. It is of interest to observe that the corresponding intermediates for PF radical decompositions with lower energy barriers are merged at higher temperatures and lower pressures. The rate constants of ipso-addition reactions are almost pressure-independence especially at higher temperatures (> 1000 K). [ABSTRACT FROM AUTHOR]

Abstract We report a cascaded group-additivity (CGA) ONIOM method for high-level energy calculations of large aliphatic hydrocarbon molecules by combining the group additivity and two-layer ONIOM methods. This hybrid method is implemented by partitioning the target molecule into individual groups, which are cascaded via the overlapping between them. The energy of the entire molecule is first calculated at a low level of theory such as M06-2x/cc-pVTZ. Then all the groups and their overlappings are treated at the levels of CCSD(T)/CBS and M06-2x/cc-pVTZ to obtain their energy difference to be used as the energy correction. We selected small-to-middle size aliphatic hydrocarbons including 79 C 4 C 8 molecules as the validation set to demonstrate the feasibility of the CGA-ONIOM method, followed by the calculations of 12 representative C 10 , C 12 and C 16 aliphatic hydrocarbons (including normal-, branched-, cyclo- and unsaturated categories). Our calculations agree well with the reference values available in the literature with the modest deviation around 1.0 kcal mol−1. Compared with the conventional CCSD(T)/CBS calculation of the whole molecule, the computational cost can be dramatically reduced by a factor of ∼102 for molecules with 10 carbons and ∼104 for molecules with 16 carbons. Considering its outstanding computational efficiency and accuracy, our proposed CGA-ONIOM method is promising for combustion chemistry studies of large fuel molecules at a high level of theory. [ABSTRACT FROM AUTHOR]

Accurate determination of the bond dissociation energies (BDEs) of large alkanes is desirable but practically impossible due to the expensive cost of high-level ab initio methods. We developed a two-layer ONIOM-CCSD(T)/CBS method which treats the high layer with CCSD(T) method and the low layer with DFT method, respectively. The accuracy of this method was validated by comparing the calculated BDEs of n-hexane with that obtained at the CCSD(T)-F12b/aug-cc-pVTZ level of theory. On this basis, the C-C BDEs of C 6 -C 20 n-alkanes were calculated systematically using the ONIOM [CCSD(T)/CBS(D-T):M06-2x/6-311++G(d,p)] method, showing a good agreement with the data available in the literature. [ABSTRACT FROM AUTHOR]

The unimolecular decomposition kinetics of methyl propanoate (MP), including the direct C−O/C−C bond fissions and molecular reaction channels, were studied by using high-level ab initio calculations and Rice–Ramsperger–Kassel–Marcus/master equation (RRKM/ME) theory. Four homolytic bond-fission and ten hydrogen transfer reactions of the MP unimolecular decomposition were identified. The phenomenological rate constants were determined using the RRKM/ME theory over a temperature range of 1000−2000 K and a pressure range of 0.01 atm to the high-pressure limit. At 1 atm, the branching ratios show that the dissociation reactions MP ↔ •CH 2 C( O)OCH 3 + CH 3 , MP ↔ CH 3 OC•( O) + C 2 H 5 and MP ↔ CH 3 CH 2 C( O)O• + CH 3 dominate MP pyrolysis over the temperature range of 1000−1500 K. Our calculated rate constants were adopted in a detailed kinetic model to reproduce the laser-absorption measured CO and CO 2 concentration time-histories during the pyrolysis of 0.2% MP/Ar in a shock tube from 1292−1551 K and at 1.6 atm. The updated mechanism accurately predicted the early-time CO and CO 2 formation over the entire temperature range. In particular, our mechanism well reproduced the CO 2 time-histories from the early-time formation to the final plateau level. [ABSTRACT FROM AUTHOR]

[Display omitted] • The CGA-ONIOM method was extended for rate constant calculation to prove it accuracy and efficiency in determining the thermodynamics and kinetics of large combustion reaction system. • A hybrid CGA-ONIOM-DFT framework was proposed to approach accurate kinetics of large reaction system with loose transition state at affordable cost. • The CGA-ONIOM-DFT framework was shown to be more efficient for larger reaction system. Accurate and efficient determination of thermodynamics and kinetics is long pursued but hindered by electronic energy calculations due to very high computational cost. In this work, we propose a Cascaded Group Additivity (CGA)-ONIOM-DFT framework targeting fast thermodynamic and kinetic predictions. We studied the reaction of cyclopentane with OH radical as a proof-of-principle demonstration. The CGA-ONIOM method accurately constructed the potential energy surface with a mean unsigned error of 0.20 kcal∙mol-1 compared to the full-level CCSD(T)/CBS results. The calculated rate constants agree well with the experimental data, suggesting the feasibility of using the CGA-ONIOM-DFT framework for combustion chemical kinetics. [ABSTRACT FROM AUTHOR]

To get a better understanding of low temperature oxidation chemistry of long-side-chain cycloalkanes, the low- and intermediate-temperature oxidation mechanisms and kinetics of ethylcyclohexane (ECH) have been investigated by using a combination of electronic-structure theory, transition state theory (TST) and Rice-Ramsberger-Kassel-Marcus/Master-Equation (RRKM/ME) theory in this work. The high pressure limit rate constants for reactions with tight transition states are obtained by the TST, while the high pressure limit rate constants for barrierless reactions are obtained by the variational transition state theory (VTST). The rate constants in the fall-off range for pressure-dependent reactions are obtained by RRKM/ME theory. Depending on the position of the extracted H atom on the ring or on the side chain, the oxidation of ECH is mainly initiated by H-abstraction with OH radical to form cyclic C 8 H 15 radicals having six isomers (R1–R6) at low (500−900 K) and intermediate (900−1100 K) temperature and in this study we focus on the kinetics of the reactions starting from these isomers. At low temperature, it is shown that, for addition reactions of O 2 to cyclic C 8 H 15 radicals, the calculated rate constants when the unpaired electron of the radicals is in the side-chain are smaller than when in the ring. The intramolecular isomerization reactions of six cycloalkylperoxy radicals (R1OO–R6OO) by H-shift can lead to a large number of hydroperoxycycloalkyl radicals (QOOH) and it is shown that the 1,5 H-shift is more competitive than the 1,6 H-shift in the R1OO–R6OO. Furthermore, unimolecular elimination reactions of QOOH can form OH, HO 2 , cyclic ethers, ketones, aldehydes and conjugated olefins. The calculated results indicate that the formation cyclic ethers of ECH oxidation are inclined to 1-oxaspiro[3.5]octane, 8-methyl-7-oxa-bicyclo[4.2.0]octane, 7-methyl-6-oxa-bicyclo[3.2.1]octane and 2-ethyl-6-oxa-bicyclo[3.1.1]heptane. At intermediate temperature, the most important reaction type of R1–R6 consumption is the C–C bond fission to form smaller products. The reaction pathways and potential energy surfaces to form the main products (ethylene, butadiene, 1-butene, and so on) of R1–R6 decomposition are also performed and the rate constants of the corresponding reactions are calculated by using the TST. Rate constants of these reactions are fitted by a nonlinear least-squares method to the form of a modified Arrhenius rate expression, which can be directly used for the modeling study of low temperature oxidation of cycloalkanes. [ABSTRACT FROM AUTHOR]

Catalytic cracking of n -decane over a platinum/lanthanum–alumina coated stainless steel tube is experimentally studied to obtain the product distributions and gas yield at a pressure of 1 atm and different temperatures 600, 650 and 700 °C. The results reveal that the higher the cracking temperature is, the higher the gas yield will be. A detailed micro-kinetic model for cracking of n -decane over a platinum/lanthanum–alumina catalyst is developed to simulate the gaseous product distribution and gas yield. In high temperature catalytic cracking systems, the interactions of gas-phase and surface reactions are very significant phenomena. Thus, the model contains a detailed gas-phase pyrolysis kinetic model along with a surface kinetic model for n -decane cracking over a platinum/alumina catalyst. The gas-phase pyrolysis kinetic model contains 304 species, 1104 reactions and the surface kinetic model contains 52 adsorbed chemical species and 218 reactions. The modeling results of the gaseous product distribution and gas yield are acceptable compared with experimental results. In order to evaluate the contribution of thermal cracking in catalytic cracking, simulation of thermal cracking of n -decane is performed by using the gas-phase pyrolysis kinetic model. The simulation results show that the contribution of thermal cracking in catalytic cracking is increasing with temperature increasing. This work provides insight at the molecular level for the kinetic process of n -decane cracking over a platinum/lanthanum–alumina catalyst. [ABSTRACT FROM AUTHOR]

[Display omitted] • Solving the accurate energy barrier calculations for H-abstraction reactions (amines + H) at a low level HF method. • Providing the accurate reaction kinetics for amines combustion modeling. • Evans-Polanyi diagram for each sub-class and the corresponding rate rule are also performed for the 154 reactions. The H-abstraction reaction kinetics of primary, secondary and tertiary amines with H atom are computed using the isodesmic reaction method. The average unsigned deviation of energy barriers is 12.40 kcal mol−1 at the HF/6-31+G(d) level compared to the CCSD(T)/CBS(D-T-Q) method but reduced to 0.75 kcal mol−1 after corrections. The calculated rate constants of all reactions and corresponding rate rules are also presented. This work solves the accurate energy barrier calculations for larger molecules reaction amines + H at a low level HF method and also provides the accurate reaction kinetics for the critical important H-abstraction reactions of amines combustion modeling. [ABSTRACT FROM AUTHOR]

The promotion effect of nitromethane (NM) on ethane ignition is studied in a heated shock tube. An unusual promotion effect of NM is observed: the ignition delay time of blends first decreases and then increases with increasing NM blending ratio, and the promotion effect peaks at blending ratio of 0.5. A model from our recent study [Fuel, 2019, 256: 115956] can reproduce the measurements and the abnormal promotion effect of NM. The kinetic analyses indicate that the radical pool establishment is slow for ethane, but much faster for NM due to the weak C–N bond. After the first-stage ignition of NM, most radicals are consumed and the radical pool needs to be re-established. In the ethane/NM blends, ethyl radicals, produced from the H-atom abstraction from ethane, can accelerate the re-establishment of the radical pool and then lead to a faster ignition delay time in comparison to neat ethane and NM, thus resulting in an abnormal promotion effect. [ABSTRACT FROM AUTHOR]

It remains a long-standing challenge to predict the reaction kinetics of large complex hydrocarbon system from first principles. Exo -tricyclo[5.2.1.02,6decane, which is further called tricyclodecane and which is the major component in JP-10 aviation fuel, and therefore its reaction with hydroxyl radical is very significant. We report high-level theoretical calculations of the rate constants of tricyclodecane + OH for the first time. We show that the exchange-correlation hybrid functional M06-2X with MG3S basis set provides an accurate and efficient calculation of the barrier heights and reaction energies. A total of 20 reaction pathways for hydrogen abstractions from chair and boat tricyclodecane conformations are considered for direct dynamics. Multi-structural canonical variational transition state theory with small-curvature tunneling (MS-CVT/SCT) is adopted to calculate the rate constants of the title reaction at 200–2000 K. The theoretical results obtained using MS-CVT/SCT with curvilinear coordinates are in fairly good agreement with the experimental measurements. We also determine the branching fractions as a function of temperature and find the tertiary abstraction from tricyclodecane is dominant. This work highlights the significance of modern DFT methods for studying combustion kinetics of large fuel molecules. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Ignition delay times for CH 4 /CH 3 NO 2 binary fuel mixtures are measured. • Rate constants for hydrogen abstraction reactions (HNO + NO 2 = NO + HONO) are calculated. • A newly updated kinetic mechanism can well reproduce the measurements. • CH 3 NO 2 can reduce the initial ignition temperature of CH 4. Abstract Ignition delay times for methane/nitromethane binary fuels with oxygen diluted in Ar ( CH 4 / CH 3 NO 2 / O 2 /Ar mixtures) are measured with a heated shock tube behind the reflected shock wave at 995–1962 K and 4–18 atm for different equivalence ratios (0.5, 1.0, and 2.0). Blending ratios for CH 3 NO 2 are varied (0, 0.1, 0.2, 0.5, and 1) to investigate the promotion of CH 3 NO 2 on CH 4 during the ignition process. OH∗ emission histories at a sidewall are used to determine the measured ignition delay times of the binary fuels mixture. Correlations for the measured ignition delay times are obtained using multiple linear regression as a function of pressure, temperature, blending ratio, and equivalence ratio. Experimental results show that a small addition of CH 3 NO 2 dramatically reduces the ignition delay times of CH 4 , and induces a weak two-stage ignition. Three literature mechanisms are examined and compared with the measured ignition delay times for CH 4 / CH 3 NO 2 binary fuels mixtures, and the mechanism from Mathieu et al. is updated and validated against the experimental data. In this mechanism, the rate constants for some important reactions are theoretically determined by quantum chemical calculation. In addition, sensitivity analysis and reaction pathway analysis as well as rate of production are carried out to further elucidate the promotion of CH 3 NO 2 on ignition of the CH 4 . [ABSTRACT FROM AUTHOR]

• Explored various isomerization and decomposition pathways for MA, MB and MC radicals, considering not only conventional C–C and C–H β- scission reactions but also including C–O β- scission reactions. • High-level theoretical calculations are conducted to obtain the rate constants for isomerization and decomposition reactions for MA, MB and MC radicals over wide temperature and pressure ranges and the thermodynamics of involved species. • Improved species concentration prediction by updating the calculated rate constants into the kinetic models. Reaction kinetics of radical isomerization and decomposition of three small unsaturated methyl esters of methyl acrylate (MA, C 4 H 6 O 2), methyl butenoate (MB, C 5 H 8 O 2) and methyl crotonate (MC, C 5 H 8 O 2) are systematically studied with high-level quantum chemistry computation. MB and MC are isomers with the C=C double bonds at different positions. The potential energy profiles for these reactions are obtained at the DLPNO-CCSD(T)/CBS(T-Q)//M062X/ma-TZVP level of theory, and the thermodynamics of the involved species are derived at the CCSD(T)/CBS(T-Q) level of theory using the atomization enthalpy method. Our results show that isomerization reactions with stable cyclic transition states have lower reaction barrier heights, making them energetically and kinetically favored. For decomposition reactions, C–C β- scission reactions are more energetically favorable than C–H β- scission reactions, and the C–O β- scission reactions to produce HCHO are the most energetically favorable. The related rate constants are calculated via solving the Rice-Ramsperger-Kassel-Marcus (RRKM)/master equation at 300–2500 K and over a pressure range of 0.01–100 atm along with the high-pressure limit. It is shown that isomerization reaction dominates at low and intermediate temperatures; while as the temperature increases, the importance of decomposition reaction becomes apparent. Pressure is found to have a significant impact on the studied reactions. Additionally, the computed rate constants of this work agree well with the available theoretical results but differ significantly from the estimated results in the literatures. Kinetic reaction mechanisms are further updated, and the results show that through incorporating the presently computed rate constants and thermodynamics, the experimental species concentration distributions can be better reproduced. This work provides the necessary rate constants and thermodynamics for the kinetic model construction of MA, MB, and MC and are expected to help establish more accurate chemical kinetic models of small unsaturated methyl esters, enriching our understanding of the combustion chemistry of biodiesel. [ABSTRACT FROM AUTHOR]

2-Ethylfuran (EF2), having similar thermophysical properties as gasoline, can be produced from biomass and has received increasing attention in recent years. The reaction of EF2 with OH radical plays a fundamental role in combustion chemistry of furan fuels. This work provides a comprehensive investigation on the reaction kinetics of the title reaction. The performance of several density functional theory methods is evaluated against the DLPNO CCSD(T)/CBS(T-Q) benchmark method. The results show that M08-HX/jun-cc-pVTZ is the best one for both abstraction and addition reactions with the lowest average unsigned deviations of 0.61 and 0.63 kcal mol−1, respectively. Multi-structural variational transition state theory combined with small-curvature tunneling approximation (MS-CVT/SCT) is employed to calculate the high-pressure limit (HPL) rate constants over a wide temperature range of 500−2000 K. The system-specific quantum Rice-Ramsperger-Kassel (SS-QRRK) method is used to obtain the pressure-dependent rate constants for addition reactions at several selected pressures from 0.01 to 100 atm. We have measured the rate constants of EF2 + OH reaction behind reflected shock wave at temperatures of 985−1342 K and pressure around 1 bar. The measured rate constants exhibit a positive temperature dependence and may be described by a three-parameter Arrhenius expression: k = 1.28 × 10 − 10 × T 6.89 exp (5318 T) (cm3 mol−1 s–1). The calculated results are in good agreement with measurements and the total rate constants exhibit a non-monotonic temperature dependence due to the competition between the abstraction and addition channels. At the HPL, the addition reaction is dominant, and the branching ratio is larger than abstraction reaction at 500–1800 K and is 0.92 at 500 K. Finally, to evaluate the performance of our calculations on the ignition delay time of EF2, three available kinetic models (Somers et al., Xu et al. and Li et al.) of EF2 are updated and the results show that the predictions of Li's model are improved. [ABSTRACT FROM AUTHOR]

Ignition delay times (IDTs) of methyl crotonate (MC), methyl 3-butanoate (MB3D), and methyl methacrylate (MMA), were systematically measured to explore the influences of the position of unsaturated C C double bond and the structure of alkyl chain on ignition characteristics of unsaturated C 5 methyl esters. Experiments were performed at 1108–1783 K and 4–16 atm with the equivalance ratio ranging from 0.25 to 2 in a shock tube. Reactivities of three unsaturated esters are similar: their IDTs increase with decreasing temperature and increasing equivalence ratio but are less sensitive to pressure. To gain the insight into differences in kinetics during fuel ignition, the literature MC, MB3D and MMA models were evaluated and the MMA model was updated. Sensitivity and reaction pathway analyses show that the hydrogen-abstraction, unimolecular decomposition, and radical addition reactions are important in controlling MC ignition. However, only hydrogen-abstraction and radical addition reactions show the significance during MB3D and MMA ignitions. Furthermore, the impact of saturation was also explored. The saturated methyl esters have slightly longer IDTs than MC, MB3D, and MMA under fuel-lean conditions with T > 1350 K, because the unsaturated methyl esters are the key intermediates and the hydrogen-abstraction reactions dominate the consumption of saturated esters. • IDTs of MB3D and MMA were measured for the first time. • Kinetic models of MC, MB3D, and MMA were evaluated and updated. • MC, MB3D, and MMA have similar ignition characteristics. • MC, MB3D, and MMA are less reactive than MB and MIB at ϕ = 0.25 with T > 1350 K. • C C double bond and alkyl chain inherently influence the reaction kinetics. [ABSTRACT FROM AUTHOR]

• Uniformity of laminar premixed flames is comprehensively studied. • Thermochemical structures are obtained by LAS measurements and CFD simulations. • Almost identical radial distribution of temperature and major products are observed. • Central H 2 O/CO 2 concentrations remain constant with varied Q coflow and Re reactant. • Flame uniformity is insensitive to Φ, but more sensitive to Q coflow and Re reactant. We performed a combined experimental and numerical study of the flame uniformity for a standard McKenna burner by investigating the spatially-resolved temperature and species concentrations in laminar CH 4 /air premixed flames. In the experiment, multi-wavelength laser absorption spectroscopy (LAS) was employed for in situ , non-intrusive, and quantitative measurements of temperature, H 2 O and CO 2. In the simulation, computational fluid dynamics (CFD) simulations were performed to model the thermochemical structures of the flames. The LAS measurements and CFD simulations were compared by varying the co-flow rate, equivalence ratio (Φ = 0.8–1.2), and the Reynolds number of the reactant flow. In general, all the simulations were in relatively good agreement with the experimental data. We observed that the flame temperature and H 2 O/CO 2 concentrations have almost the identical radial distributions with a certain non-uniformity, which should be carefully considered when using the standard flame for combustion research. In particular, the flame uniformity could be improved by increasing the Reynolds number of reactant flow or reducing the co-flow rate. [ABSTRACT FROM AUTHOR]

• Two-stage ignition delay times are measured at broader experimental conditions. • First-stage ignition delay time decreases with increasing equivalence ratio below 1150 K. • The intensity of second OH* peak is indiscernible at fuel-rich or low temperature condition. • CH 3 + NO = H 2 CN + OH shows importance for second-stage ignition at fuel-rich condition. Two-stage ignition of nitromethane diluted in Ar is investigated at various equivalence ratios (0.2–0.5), dilution levels (93%–97%), and pressures (4–16 atm) with a heated shock tube apparatus. OH* emission profiles are used to determine ignition delay times. The second-stage ignition delay time increases with increasing equivalence ratio or dilution level, but is insensitive to pressure especially at high dilution levels. The first-stage ignition delay time is unaffected by the present experimental parameters above 1150 K, below which it decreases with increasing equivalence ratio or pressure. An updated model reconsidering reaction CH 3 + NO = H 2 CN + OH is examined against the experimental measurements from present work and literature, including ignition delay times, laminar burning velocities, and species mole fraction profiles. At fuel-rich condition, this reaction has a significant contribution to the formation of OH radical during the second-stage ignition. The two-stage ignition and intensity evolution of OH peaks are well predicted and explained kinetically by the updated model. [ABSTRACT FROM AUTHOR]

To better understand the combustion chemistry and improve the model performance of aliphatic amines, the kinetics of H-abstraction reactions from n -propylamine (NPA) by H, CH 3 , OH, and NH 2 radicals and the ignition characteristics of NPA are investigated. The CCSD(T)-F12/cc-pVTZ-F12 method is selected as the benchmark, and the performances of several density functional theory methods are evaluated by comparing the calculated reaction energies and barrier heights against the benchmark values. The M06-2X/jun-cc-pVTZ method is identified as the best one with a mean unsigned deviation of 0.59 kcal mol−1. With the selected method, the rate constants are calculated using the variational transition-state theory combined with the small-curvature tunneling and multi-structural torsional anharmonicity (MS-CVT/SCT) options at 298–2000 K. The H-abstraction reactions at the α -C site are the dominant channels for NPA + H/ CH 3 / NH 2 , but this channel is less important for NPA + OH due to the significant variational effect. The ignition characteristics of NPA is studied in a shock tube at 1105–1441 K, 4–20 atm, and different equivalence ratios (0.5, 1.0, and 2.0). The ignition delay time of NPA decreases noticeably with increasing temperature and pressure, while it is insensitive to equivalence ratio. Based on our calculations, a literature model is updated and then assessed against the measured ignition delay times. The updated model shows a better agreement with the measurements but fails to predict the ignition behavior of NPA under certain conditions. The reaction pathway and sensitivity analyses demonstrate that the unsaturated aliphatic amines and imines (such as CH 3 CHCHNH 2 and CH 2 NH) are the important nitrogen-containing intermediates, and further investigation of the subset of these species is needed to improve the combustion model of aliphatic amines. • The rate constants of n -propylamine with H, CH 3 , OH, and NH 2 radicals are theoretically determined. • Ignition delay times of n -propylamine are reported for the first time using a shock tube. • The literature combustion model is updated and validated against the measurements. • Kinetic analyses are implemented to interpret the combustion chemistry of n -propylamine; [ABSTRACT FROM AUTHOR]

The ignition characteristics of methyl acrylate (MA) and vinyl acetate (VA) are investigated in a heated shock tube at 1176–1618 K, 4–16 atm, and equivalence ratios of 0.5–2.0. The ignition delay times of MA and VA decrease with increasing equivalence ratio and decreasing pressure but pressure has a negligible effect on their ignition at low temperatures. Comparison between ignition delay times of MA and VA as well as their corresponding saturated esters indicates that both saturation and position of C C double bond affect the ignition process. To reveal its chemical kinetics on ignition characteristics of esters, the existing kinetic model of MA is updated and VA model is further constructed based on the updated MA model. The new kinetic models can better reproduce ignition delay times under current experimental conditions. Comparisons and kinetic analyses demonstrate that MA is more active than VA and H-addition and unimolecular decomposition reactions are the major channels consuming fuel molecules. The reactivities of MA and VA are lower than their corresponding saturated esters at φ = 0.5 and 1. With increasing temperature and equivalence ratio, the saturated esters become less active than MA and VA because of low decomposition rate and stable intermediate formations, respectively. • Ignition delay times of vinyl acetate (VA) are first measured in shock tube. • Kinetic models are updated and constructed for methyl acrylate (MA) and VA. • Unsaturated methyl ester MA is more reactive than unsaturated acetic ester VA. • MA and VA are less reactive than corresponding saturated esters at φ = 0.5 and 1. • Unsaturated esters are more reactive at high temperatures (>1480 K) and φ = 2. [ABSTRACT FROM AUTHOR]

We report the first demonstration of heterodyne phase-sensitive dispersion spectroscopy (HPSDS) for the simultaneous temperature and H2O concentration measurements in combustion environments. Two continuous-wave distributed-feedback quantum cascade lasers (DFB-QCLs) at 5.27 and 10.53 µm were used to exploit the strong H2O transitions (1897.52 and 949.53 cm−1) at high temperatures. The injection current of each QCL was modulated at sub-GHz or GHz to generate the three-tone radiation and the dispersion signal was detected by the radio-frequency down-conversion heterodyning. The peak-to-peak ratio of the two H2O dispersion spectra exhibits a monotonic relationship with temperature over the temperature range of 1000-3000 K, indicating the capability of performing two-line thermometry using laser dispersion spectroscopy. We measured the temperatures of CH4/air flames at different equivalence ratios (Φ = 0.8-1.2), yielding a good agreement with the corresponding thermocouple measurements. In addition, one-dimensional kinetic modeling coupled with a detailed chemical kinetic mechanism (GRI 3.0) was conducted to compare with the measured H2O concentrations using HPSDS. Finally, we demonstrated HPSDS is immune to optical power fluctuations by measuring the dispersion spectra at varied incident laser powers. [ABSTRACT FROM AUTHOR]