| 1. |
- 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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| 2. |
- Matveev, Sergey S., et al.
(författare)
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Laminar burning velocities of surrogate components blended with ethanol
- 2019
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Ingår i: Combustion and Flame. - : Elsevier BV. - 0010-2180. ; 209, s. 389-393
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Tidskriftsartikel (refereegranskat)abstract
- To provide a consistent database for all important classes of hydrocarbons considered as components of surrogate mixtures, laminar burning velocities of n-decane, p-xylene and methylcyclohexane blended with ethanol were determined using the heat flux method at atmospheric pressure and initial temperatures of 318–400 K. The results obtained at Samara University and Lund University are within overlapping experimental uncertainties. Moreover, data consistency for MCH + ethanol blends was assessed with the help of analysis of the temperature dependence of the laminar burning velocity. Present experiments were modelled using the PoliMi detailed kinetic mechanism. Its predictions were found in a good agreement with the measurements performed with n-decane, while burning velocities of methylcyclohexane and p-xylene were over- and underpredicted, respectively. In all cases, the burning velocity of ethanol is higher than that of the hydrocarbons studied, while the burning velocity of the blends is in-between the values for the neat components.
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| 3. |
- Matveev, V. V., et al.
(författare)
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Investigation of Melts of Polybutylcarbosilane Dendrimers by 1H NMR Spectroscopy
- 2017
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Ingår i: Scientific Reports. - : Nature Publishing Group. - 2045-2322. ; 7:1
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Tidskriftsartikel (refereegranskat)abstract
- Melts of polybutylcarbosilane (PBC) dendrimers from third (G3) up to sixth (G6) generations are investigated by 1H NMR spectroscopy in a wide temperature range up to 493 K. At room temperature, NMR spectra of G3-G5 dendrimers exhibit resolved, solution-like spectra ("liquid" phase). In contrast, the spectrum of the G6 dendrimer is characterized by a single unresolved broad line at whole temperature range, which supports the presence of an anomalous phase state of G6 at temperatures higher than glass transition temperature. For the first time, an unexpected transition of G5 dendrimer from a molecular liquid state to an anomalous state/phase upon temperature increase has been detected using NMR data. Specifically, an additional wide background line appears in the G5 spectrum above 473 K, and this line corresponds to a G5 state characterized by restricted molecular mobility, i.e., a state similar to the "anomalous" phase of G6 melt. The fraction of the G5 dendrimers in "anomalous" phase at 493 K is approximately 40%. Analysis of the spectral shapes suggests that changes in the G5 dendrimers are reversible with temperature.
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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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