| 1. |
- Shmakov, A. G., et al.
(författare)
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Formation and consumption of NO in H-2 + O-2 + N-2 flames doped with NO or NH3 at atmospheric pressure
- 2010
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Ingår i: Combustion and Flame. - : Elsevier BV. - 0010-2180. ; 157:3, s. 556-565
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Tidskriftsartikel (refereegranskat)abstract
- Flat premixed burner-stabilized H-2 + O-2 + N-2 flames, neat or doped with 300-1000 ppm of NO or NH3, were studied experimentally using molecular-beam mass-spectrometry and simulated numerically. Spatial profiles of temperature and concentrations of stable species, H-2, O-2, H2O, NO, NH3, and of H and OH radicals obtained at atmospheric pressure in lean (phi = 0.47), near-stoichiometric (phi = 1.1) and rich (phi = 2.0) flames are reported. Good agreement between measured and calculated structure of lean and near-stoichiometric flames was found. Significant discrepancy between simulated and measured profiles of NO concentration was observed in the rich flames. Sensitivity and reaction path analyses revealed reactions responsible for the discrepancy. Modification to the model was proposed to improve an overall agreement with the experiment. (C) 2009 The Combustion Institute. Published by Elsevier Inc. All rights reserved.
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| 2. |
- Alekseev, Vladimir A., et al.
(författare)
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High-temperature oxidation of acetylene by N2O at high Ar dilution conditions and in laminar premixed C2H2 + O2 + N2 flames
- 2022
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Ingår i: Combustion and Flame. - : Elsevier BV. - 0010-2180. ; 238
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Tidskriftsartikel (refereegranskat)abstract
- High-temperature oxidation of acetylene (C2H2) is studied behind reflected shock waves and in laminar flames. Atomic resonance absorption spectroscopy (ARAS) is employed to record oxygen atom concentration profiles for the mixture of 10 ppm C2H2 + 10 ppm N2O + argon and temperatures from 1688 K to 3179 K, extending the range of such data available from the literature. Laminar burning velocity of C2H2 in a diluted oxidizer with 11–13% O2 in the O2 + N2 mixture is measured using the heat flux method and compared to the literature data for the 13% O2 mixture. An updated detailed kinetic mechanism is presented to model and analyze the results, and the selection of rate constants in the C2H2 sub-mechanism, whose importance was identified by the sensitivity analysis, is discussed. The performance of the new model is compared against several reaction schemes available from the literature, and kinetic differences between them are outlined. The new shock-wave data helped to improve the performance of the present model compared to its previous version. For the laminar flames, a particular importance of reactions involving C2H3 is identified, however, the reasons for the observed differences in model predictions are to a large extent located outside the C2H2 sub-mechanism, which were also identified.
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| 3. |
- Gerasimov, Ilya E., et al.
(författare)
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Methyl-3-hexenoate combustion chemistry : Experimental study and numerical kinetic simulation
- 2020
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Ingår i: Combustion and Flame. - : Elsevier BV. - 0010-2180. ; 222, s. 170-180
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Tidskriftsartikel (refereegranskat)abstract
- This work represents a detailed investigation of combustion and oxidation of methyl-3-hexenoate (CAS Number 2396-78-3), including experimental studies of combustion and oxidation characteristics, quantum chemistry calculations and kinetic model refinement. Following experiments have been carried out: Speciation measurements during oxidation in a jet-stirred reactor at 1 atm; chemical speciation measurements in a stoichiometric premixed flame at 1 atm using molecular-beam mass-spectrometry; ignition delay times measurements in a shock tube at 20 and 40 bar; and laminar burning velocity measurements at 1 atm using a heat-flux burner over a range of equivalence ratios. An updated detailed chemical kinetic mechanism for methyl-3-hexenoate combustion based on previous studies was proposed and validated against the novel experimental data and the relevant data available in literature with satisfactory agreement. Sensitivity and reaction pathway analyses were performed to show main decomposition pathways of methyl-3-hexenoate and underline possible sources of disagreements between experiments and simulations.
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| 4. |
- Savchenkova, Anna S., et al.
(författare)
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Mechanism and rate constants of the CH2 + CH2CO reactions in triplet and singlet states : A theoretical study
- 2019
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Ingår i: Journal of Computational Chemistry. - : Wiley. - 0192-8651 .- 1096-987X. ; 40:2, s. 387-399
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Tidskriftsartikel (refereegranskat)abstract
- Ab initio and density functional CCSD(T)-F12/cc-pVQZ-f12//B2PLYPD3/6-311G** calculations have been performed to unravel the reaction mechanism of triplet and singlet methylene CH2 with ketene CH2CO. The computed potential energy diagrams and molecular properties have been then utilized in Rice–Ramsperger–Kassel–Marcus-Master Equation (RRKM-ME) calculations of the reaction rate constants and product branching ratios combined with the use of nonadiabatic transition state theory for spin-forbidden triplet-singlet isomerization. The results indicate that the most important channels of the reaction of ketene with triplet methylene lead to the formation of the HCCO + CH3 and C2H4 + CO products, where the former channel is preferable at higher temperatures from 1000 K and above. In the C2H4 + CO product pair, the ethylene molecule can be formed either adiabatically in the triplet electronic state or via triplet-singlet intersystem crossing in the singlet electronic state occurring in the vicinity of the CH2COCH2 intermediate or along the pathway of CO elimination from the initial CH2CH2CO complex. The predominant products of the reaction of ketene with singlet methylene have been shown to be C2H4 + CO. The formation of these products mostly proceeds via a well-skipping mechanism but at high pressures may to some extent involve collisional stabilization of the CH3CHCO and cyclic CH2COCH2 intermediates followed by their thermal unimolecular decomposition. The calculated rate constants at different pressures from 0.01 to 100 atm have been fitted by the modified Arrhenius expressions in the temperature range of 300–3000 K, which are proposed for kinetic modeling of ketene reactions in combustion.
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| 5. |
- Savchenkova, Anna S., et al.
(författare)
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Revisiting diacetyl and acetic acid flames : The role of the ketene + OH reaction
- 2020
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Ingår i: Combustion and Flame. - : Elsevier BV. - 0010-2180. ; 218, s. 28-41
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Tidskriftsartikel (refereegranskat)abstract
- The mechanism of the reaction of ketene with hydroxyl radical has been studied by ab initio CCSD(T)-F12/cc-pVQZ-F12//B3LYP/6-311G(d,p) calculations of the potential energy surface. Temperature- and pressure-dependent reaction rate constants have been computed using the RRKM-Master Equation and transition state theory methods in the temperature range of 300–3000 K and in the pressure range of 0.01–100 atm. Three main channels have been analyzed: through direct abstraction of H atoms or starting with OH addition to the terminal carbon and to the central carbon atoms. Major products identified agree with the recent theoretical studies, however, significant difference was found with the rate constants derived by Xu et al. [13] and Cavallotti et al. [11]. To investigate the impact of the choice of reactions between CH2CO and OH radicals on the predicted burning velocities of the flames sensitive to ketene chemistry, namely diacetyl and acetic acid flames, a detailed kinetic mechanism was updated with pertinent reactions suggested in the literature. Then the rate constants of four most important product channels of reaction CH2CO + OH forming HCCO + H2O, CH2OH + CO, CH3 + CO2 and CH2COOH from the present and from the recent theoretical studies were tested. Good agreement with the burning velocities of diacetyl + air flames was found for the present model, while the expressions from the literature underestimate them. On the contrary, any combination of the rate constants of reactions between ketene and hydroxyl radical overpredicts burning velocities of acetic acid + air flames, which strongly indicates that the kinetic model of acetic acid is most probably incomplete and requires consideration of additional reactions.
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| 6. |
- Alekseev, Vladimir A., et al.
(författare)
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Data consistency of the burning velocity measurements using the heat flux method : Hydrogen flames
- 2018
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Ingår i: Combustion and Flame. - : Elsevier BV. - 0010-2180. ; 194, s. 28-36
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Tidskriftsartikel (refereegranskat)abstract
- Consistent datasets of experiments are highly important both for validation and optimization of kinetic mechanisms. An analysis of the data consistency of all available burning velocity measurements of hydrogen flames using the heat flux method at atmospheric pressure is performed in the present work. A comparison of many experiments performed in several laboratories with different types of dilution by various inerts was guided by kinetic modeling using two kinetic mechanisms. Konnov (2015) and ELTE (Varga et al., 2016) models demonstrated a uniform trend at all conditions tested: the second mechanism predicts lower burning velocities which are in better agreement with the heat flux measurements from different groups. Some experimental datasets, however, significantly disagree with one or both models; these conditions were revisited experimentally in the present work. The laminar burning velocities of H2 + O2 + N2 mixtures with 7.7% O2 in O2 + N2 oxidizer and of 85:15 (H2 + N2) and 25:75 (H2 + N2) fuel mixtures with 12.5:87.5 (O2 + He) oxidizer have been measured. It was concluded that the results of Hermanns et al. (2007) are somewhat higher than those of other studies at similar conditions and a possible reason of this disagreement was suggested. Analysis of the measurements performed by Goswami et al. (2015) on a high-pressure installation suggests an equipment malfunction that led to the erroneous values of the equivalence ratio for hydrogen and syngas flames. The ELTE mechanism developed using an optimization approach shows a very good performance in predicting laminar burning velocities of hydrogen flames measured using the heat flux method.
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| 7. |
- Alekseev, Vladimir A., et al.
(författare)
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Laminar burning velocities of methylcyclohexane + air flames at room and elevated temperatures : A comparative study
- 2018
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Ingår i: Combustion and Flame. - : Elsevier BV. - 0010-2180. ; 196, s. 99-107
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Tidskriftsartikel (refereegranskat)abstract
- Laminar burning velocities of methylcyclohexane + air flames were determined using the heat flux method at atmospheric pressure and initial temperatures of 298–400 K. The measurements were performed on two experimental setups at Lund University and Samara National Research University. Our results obtained at the same initial temperatures are in good agreement. Consistency of the measurements performed at different temperatures was tested employing analysis of the temperature dependence of the burning velocities. This analysis revealed increased scatter in the burning velocity data at some equivalence ratios which may be attributed to the differences in the design of the burners used. New measurements were also compared to available literature data. Reasonably good agreement with the data of Kumar and Sung (2010) was observed at 400 K, with significantly higher burning velocities at the maximum at 353 K as compared to other studies from the literature. Predictions of two detailed reaction mechanisms developed for jet fuels – PoliMi and JetSurF 2.0 were compared with the present generally consistent measurements. The two kinetic models disagreed with each other, with the experimental data being located in between the model predictions. Sensitivity analysis revealed that behavior of the models is largely defined by C0–C2 chemistry. Comparison of the model predictions with the burning velocities of ethylene and methane showed the same trends in over- and under-predictions as for methylcyclohexane + air flames.
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| 8. |
- Brackmann, Christian, et al.
(författare)
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Strategy for improved NH2 detection in combustion environments using an Alexandrite laser
- 2017
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Ingår i: Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy. - : Elsevier BV. - 1386-1425. ; 184, s. 235-242
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Tidskriftsartikel (refereegranskat)abstract
- A new scheme for NH2 detection by means of laser-induced fluorescence (LIF) with excitation around wavelength 385 nm, accessible using the second harmonic of a solid-state Alexandrite laser, is presented. Detection of NH2 was confirmed by identification of corresponding lines in fluorescence excitation spectra measured in premixed NH3-air flames and on NH2 radicals generated through NH3 photolysis in a nonreactive flow at ambient conditions. Moreover, spectral simulations allow for tentative NH2 line identification. Dispersed fluorescence emission spectra measured in flames and photolysis experiments showed lines attributed to vibrational bands of the NH2 A2A1 ← X2B1 transition but also a continuous structure, which in flame was observed to be dependent on nitrogen added to the fuel, apparently also generated by NH2. A general conclusion was that fluorescence interferences need to be carefully considered for NH2 diagnostics in this spectral region. Excitation for laser irradiances up to 0.2 GW/cm2 did not result in NH2 fluorescence saturation and allowed for efficient utilization of the available laser power without indication of laser-induced photochemistry. Compared with a previously employed excitation/detection scheme for NH2 at around 630 nm, excitation at 385.7 nm showed a factor of ~ 15 higher NH2 signal. The improved signal allowed for single-shot NH2 LIF imaging on centimeter scale in flame with signal-to-noise ratio of 3 for concentrations around 1000 ppm, suggesting a detection limit around 700 ppm. Thus, the presented approach for NH2 detection provides enhanced possibilities for characterization of fuel-nitrogen combustion chemistry.
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| 9. |
- Burke, Sinead M., et al.
(författare)
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An experimental and modeling study of propene oxidation. Part 2: Ignition delay time and flame speed measurements
- 2015
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Ingår i: Combustion and Flame. - : Elsevier BV. - 0010-2180. ; 162:2, s. 296-314
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Tidskriftsartikel (refereegranskat)abstract
- Experimental data obtained in this study (Part II) complement the speciation data presented in Part I, but also offer a basis for extensive facility cross-comparisons for both experimental ignition delay time (IDT) and laminar flame speed (LFS) observables. To improve our understanding of the ignition characteristics of propene, a series of IDT experiments were performed in six different shock tubes and two rapid compression machines (RCMs) under conditions not previously studied. This work is the first of its kind to directly compare ignition in several different shock tubes over a wide range of conditions. For common nominal reaction conditions among these facilities, cross-comparison of shock tube IDTs suggests 20-30% reproducibility (2 sigma) for the IDT observable. The combination of shock tube and RCM data greatly expands the data available for validation of propene oxidation models to higher pressures (2-40 atm) and lower temperatures (750-1750 K). Propene flames were studied at pressures from 1 to 20 atm and unburned gas temperatures of 295-398 K for a range of equivalence ratios and dilutions in different facilities. The present propene-air LFS results at 1 atm were also compared to LFS measurements from the literature. With respect to initial reaction conditions, the present experimental LFS cross-comparison is not as comprehensive as the IDT comparison; however, it still suggests reproducibility limits for the LFS observable. For the LFS results, there was agreement between certain data sets and for certain equivalence ratios (mostly in the lean region), but the remaining discrepancies highlight the need to reduce uncertainties in laminar flame speed experiments amongst different groups and different methods. Moreover, this is the first study to investigate the burning rate characteristics of propene at elevated pressures (>5 atm). IDT and LFS measurements are compared to predictions of the chemical kinetic mechanism presented in Part I and good agreement is observed. (C) 2014 The Combustion Institute. Published by Elsevier Inc. All rights reserved.
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| 10. |
- Capriolo, Gianluca, et al.
(författare)
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An experimental and kinetic study of propanal oxidation
- 2018
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Ingår i: Combustion and Flame. - : Elsevier BV. - 0010-2180. ; 197, s. 11-21
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Tidskriftsartikel (refereegranskat)abstract
- Propanal is a critical stable intermediate derived from the oxidation of 1-propanol, a promising alcohol fuel additive. To deepen the knowledge and accurately describe propanal combustion characteristics, new burning velocity measurements at different temperatures were carried out and a new detailed kinetic mechanism for propanal was proposed. Experiments were performed using the heat flux method and compared with literature data. Important discrepancies were noted between the new and available data, and possible reasons were suggested. Flow rate sensitivity analysis highlighted that, as expected, the important reactions influencing the propanal oxidation in flames are pertinent to H2 and CO sub-mechanism. Current mechanism is based on the most recent Konnov model, extended to include propanal chemistry subset. Rate constant parameters were selected based on careful evaluation of experimental and theoretical data available in literature. Model validation included assessment against a large set of combustion experiments obtained at different regimes, i.e. flames, shock tubes, and well stirred reactor, as well as comparison with the semi-detailed (lumped) kinetic mechanism for hydrocarbon and oxygenated fuels from Politecnico di Milano, detailed kinetic model from Veloo et al. and low temperature oxidation of aldehydes kinetic model of Pelucchi et al. The proposed model reproduced experimental burning velocities, ignition delay times, flame structure and JSR data with an overall good fidelity, while it reproduces only qualitatively the species distribution of propanal pyrolysis.
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