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1.	Shmakov, A. G., et al. (author) Formation and consumption of NO in H-2 + O-2 + N-2 flames doped with NO or NH3 at atmospheric pressure 2010 In: Combustion and Flame. - : Elsevier BV. - 0010-2180. ; 157:3, s. 556-565 Journal article (peer-reviewed)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.
2.	Alekseev, Vladimir A., et al. (author) High-temperature oxidation of acetylene by N2O at high Ar dilution conditions and in laminar premixed C2H2 + O2 + N2 flames 2022 In: Combustion and Flame. - : Elsevier BV. - 0010-2180. ; 238 Journal article (peer-reviewed)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.
3.	Gerasimov, Ilya E., et al. (author) Methyl-3-hexenoate combustion chemistry : Experimental study and numerical kinetic simulation 2020 In: Combustion and Flame. - : Elsevier BV. - 0010-2180. ; 222, s. 170-180 Journal article (peer-reviewed)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.
4.	Savchenkova, Anna S., et al. (author) Mechanism and rate constants of the CH2 + CH2CO reactions in triplet and singlet states : A theoretical study 2019 In: Journal of Computational Chemistry. - : Wiley. - 0192-8651 .- 1096-987X. ; 40:2, s. 387-399 Journal article (peer-reviewed)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.
5.	Savchenkova, Anna S., et al. (author) Revisiting diacetyl and acetic acid flames : The role of the ketene + OH reaction 2020 In: Combustion and Flame. - : Elsevier BV. - 0010-2180. ; 218, s. 28-41 Journal article (peer-reviewed)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.
6.	Alekseev, Vladimir A., et al. (author) Data consistency of the burning velocity measurements using the heat flux method : Hydrogen flames 2018 In: Combustion and Flame. - : Elsevier BV. - 0010-2180. ; 194, s. 28-36 Journal article (peer-reviewed)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.
7.	Alekseev, Vladimir A., et al. (author) Laminar burning velocities of methylcyclohexane + air flames at room and elevated temperatures : A comparative study 2018 In: Combustion and Flame. - : Elsevier BV. - 0010-2180. ; 196, s. 99-107 Journal article (peer-reviewed)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.
8.	Brackmann, Christian, et al. (author) Strategy for improved NH2 detection in combustion environments using an Alexandrite laser 2017 In: Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy. - : Elsevier BV. - 1386-1425. ; 184, s. 235-242 Journal article (peer-reviewed)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.
9.	Burke, Sinead M., et al. (author) An experimental and modeling study of propene oxidation. Part 2: Ignition delay time and flame speed measurements 2015 In: Combustion and Flame. - : Elsevier BV. - 0010-2180. ; 162:2, s. 296-314 Journal article (peer-reviewed)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.
10.	Capriolo, Gianluca, et al. (author) An experimental and kinetic study of propanal oxidation 2018 In: Combustion and Flame. - : Elsevier BV. - 0010-2180. ; 197, s. 11-21 Journal article (peer-reviewed)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.
11.	Dakshnamurthy, Shanmugasundaram, et al. (author) Experimental Study and a Short Kinetic Model for High-Temperature Oxidation of Methyl Methacrylate 2019 In: Combustion Science and Technology. - : Informa UK Limited. - 0010-2202 .- 1563-521X. ; 191:10, s. 1789-1814 Journal article (peer-reviewed)abstract Synthetic and natural polymeric esters find applications in transport and construction sectors, where fire safety is an important concern. One polymer that is widely used is poly (methyl methacrylate) (PMMA), which almost completely undergoes thermal decomposition into methyl methacrylate (its monomer) CH2=C(CH3) - C(= O) - O - CH3 (MMA) at ~250–300°C. In order to analyze the high-temperature gas-phase oxidation of PMMA, and thereby predict its fire behavior (such as burning rate, temperature of the material, and heat fluxes) with less computational effort, a compact kinetic model for the oxidation of its primary decomposition product, MMA, is most essential. This is accomplished in the present work by obtaining a reduced mechanism for MMA oxidation from a detailed mechanism from the Lawrence Livermore National Laboratories group. To extend the available data base for model validation and present validation data at atmospheric pressure conditions, for the first time, (i) detailed measurements of species profiles have been performed in stoichiometric laminar flat flames using flame sampling molecular beam mass spectrometry (MBMS) technique and (ii) laminar burning velocities have been obtained using the heat flux method for various unburnt mixture temperatures. Evaluating the model against these data sets point to the need to revise the kinetic model, which is achieved by adopting rate constants of key reactions among analogous molecules from recent literature. The updated compact kinetic model is able to predict the major species in the flat flame as well as the burning velocity of MMA satisfactorily. The final “short MMA mechanism” consists of 88 species and 1084 reactions.
12.	Dirrenberger, P., et al. (author) Laminar burning velocity of gasolines with addition of ethanol 2014 In: Fuel. - : Elsevier BV. - 1873-7153 .- 0016-2361. ; 115, s. 162-169 Journal article (peer-reviewed)abstract The adiabatic laminar burning velocities of a commercial gasoline and of a model fuel (n-heptane, iso-octane, and toluene mixture) of close research octane number have been measured at 358 K. Non-stretched flames were stabilized on a perforated plate burner at 1 atm. The heat flux method was used to determine burning velocities under conditions for which the net heat loss of the flame is zero. Very similar values of flame velocities have been obtained for the commercial gasoline and for the proposed model fuel. The influence of ethanol as an oxygenated additive has been investigated for these two fuels and has been found to be negligible for values up to 15% (vol). Measurements were also performed for ethanol and the three pure components of the model fuel at 298, 358 and 398 K. The results obtained for the studied mixtures, and for pure n-heptane, iso-octane, toluene and ethanol, have been satisfactorily simulated using a detailed kinetic mechanism. (C) 2013 Elsevier Ltd. All rights reserved.
13.	Fomin, Alexey, et al. (author) Experimental and modelling study of 1CH2 in premixed very rich methane flames 2016 In: Combustion and Flame. - : Elsevier BV. - 0010-2180. ; 171, s. 198-210 Journal article (peer-reviewed)abstract Stoichiometric and very rich (1.5 ≤ ɸ ≤ 1.9) laminar flat flames of methane have been investigated using nonintrusive laser diagnostics. Premixed CH4 + O2 + N2 flames were stabilized at a pressure of 30 ± 0.3 Torr. Temperature profiles were obtained using laser-induced fluorescence of OH. Absolute concentration profiles of singlet methylene, 1CH2, were measured by intracavity laser absorption spectroscopy. Uncertainties of the relative and absolute concentrations of singlet methylene were evaluated to be about ±10% and ±30%, respectively. These new experimental data were compared with predictions of three detailed kinetic mechanisms: GRI-mech. 3.0, Aramco mech. 1.3, and the model under development in Lund. In the last mechanism 78 rate constants of reactions along the pathway CH3 → 1CH2 → 3CH2 → CH were reviewed and updated. No adjustment or tuning of the rate expressions to accommodate experimental results was attempted. GRI-mech. significantly overpredicts singlet methylene concentrations in all flames. Aramco mech. and the present model are in good agreement with the measurements in stoichiometric flame, while in all rich flames only the present mechanism reproduces spatial profiles of 1CH2. Detailed analysis of the behaviour of these models revealed that omission of the reaction 1CH2 + M = 3CH2 + M is the main reason of the discrepancy between predictions of the Aramco 1.3 and GRI-mech. 3.0 and experimental 1CH2 concentrations in rich flames.
14.	Ahmed, Ahfaz, et al. (author) Kinetic modelling and experimental study of small esters : Methyl acetate and ethyl acetate 2017 In: 11th Asia-Pacific Conference on Combustion, ASPACC 2017. ; 2017-December Conference paper (peer-reviewed)abstract A detailed chemical kinetic mechanism comprising methyl acetate and ethyl acetate has been developed based on the previous work by Westbrook et al. [1]. The newly developed kinetic mechanism has been updated with new reaction rates from recent theoretical studies. To validate this model, shock tube experiments measuring ignition delay time have been conducted at 15 & 30 bar and equivalence ratio 0.5, 1.0 and 2.0. Another set of experiments measuring laminar burning velocity was also performed on a heat flux burner at atmospheric pressure over wide range of equivalence ratios [ ~ 0.7-1.4]. The new mechanism shows significant improvement in prediction of experimental data over earlier model across the range of experiments.In this study, a detailed chemical kinetic model for methyl and ethyl acetate (Fig. 1) has been developed. This model is advanced from the mechanism proposed for laminar premixed flames by Westbrook and coworkers in 2009 [1]. Acetates studied in this work are both high RON fuels with suitable physical and chemical properties [Table 1] to be considered as potential fuels in advanced gasoline engines [4]. Shock tube experiments measuring ignition delay time have been conducted at 15 & 30 bar and equivalence ratio 0.5, 1.0 and 2.0. Another set of experiments measuring laminar burning velocity have also been performed on a heat flux burner at atmospheric pressure over wide range of equivalence ratios. The model developed in this work shows good agreement with ignition data and laminar burning velocity data across the temperature and equivalence ratio range respectively.
15.	Ahmed, Ahfaz, et al. (author) Small ester combustion chemistry : Computational kinetics and experimental study of methyl acetate and ethyl acetate 2019 In: Proceedings of the Combustion Institute. - : Elsevier BV. - 1540-7489. ; 37:1, s. 419-428 Journal article (peer-reviewed)abstract Small esters represent an important class of high octane biofuels for advanced spark ignition engines. They qualify for stringent fuel screening standards and could be synthesized through various pathways. In this work, we performed a detailed investigation of the combustion of two small esters, MA (methyl acetate) and EA (ethyl acetate), including quantum chemistry calculations, experimental studies of combustion characteristics and kinetic model development. The quantum chemistry calculations were performed to obtain rates for H-atom abstraction reactions involved in the oxidation chemistry of these fuels. The series of experiments include: a shock tube study to measure ignition delays at 15 and 30 bar, 1000-1450 K and equivalence ratios of 0.5, 1.0 and 2.0; laminar burning velocity measurements in a heat flux burner over a range of equivalence ratios [0.7-1.4] at atmospheric pressure and temperatures of 298 and 338 K; and speciation measurements during oxidation in a jet-stirred reactor at 800-1100 K for MA and 650-1000 K for EA at equivalence ratios of 0.5, 1.0 and at atmospheric pressure. The developed chemical kinetic mechanism for MA and EA incorporates reaction rates and pathways from recent studies along with rates calculated in this work. The new mechanism shows generally good agreement in predicting experimental data across the broad range of experimental conditions. The experimental data, along with the developed kinetic model, provides a solid groundwork towards improving the understanding the combustion chemistry of smaller esters.
16.	Bardin, Maxim E., et al. (author) Laminar Burning Velocities of Dimethyl Carbonate with Air 2013 In: Energy & Fuels. - : American Chemical Society (ACS). - 0887-0624 .- 1520-5029. ; 27:9, s. 5513-5517 Journal article (peer-reviewed)abstract Laminar burning velocities of dimethyl carbonate (DMC) + air flames at initial gas mixture temperatures of 298, 318, 338, and 358 K are reported. Nonstretched flames were stabilized on a perforated plate burner at atmospheric pressure, and the laminar burning velocities were determined using the heat flux method. The overall accuracy of the burning velocities was evaluated to be typically better than +/- 1 cm/s. The effects of unburned mixture temperature on the laminar burning velocity of DMC were analyzed using the correlation S-L = S (T-u/T-u0)(alpha). The present experimental results indicated that the power exponent a reaches a minimum in slightly rich mixtures corresponding to the maximum burning velocity. Modeling of these results has been attempted using the mechanism developed by Glaude et al. It was found that this model significantly overpredicts laminar burning velocities of methanol, ethanol, and DMC; however, it accurately reproduces the temperature power exponent alpha for dimethyl carbonate flames.
17.	Brackmann, Christian, et al. (author) Experimental and modeling study of nitric oxide formation in premixed methanol + air flames 2020 In: Combustion and Flame. - : Elsevier BV. - 0010-2180. ; 213, s. 322-330 Journal article (peer-reviewed)abstract Validation and further development of models for alcohol combustion requires accurate experimental data obtained under well-controlled conditions. To this end, measurements of nitric oxide, NO, mole fractions in premixed laminar methanol + air flames have been performed using saturated laser-induced fluorescence, LIF. The methanol flames have been stabilized at atmospheric pressure and initial gas temperature of 318 K at equivalence ratios ɸ = 0.7–1.5 using the heat flux method that allows for simultaneous determination of their laminar burning velocity. The LIF signal is converted into NO mole fraction via calibration measurements, which have been performed in flames of methane, methanol and syngas seeded with known amounts of NO. The experimental approach is verified by the measurements of NO mole fractions in the post flame zone of methane flames, investigated in previous studies at similar conditions. Data on the NO formation together with burning velocities for methanol and methane obtained under adiabatic flame conditions provide highly valuable input for model validation. They have been compared with predictions of six different chemical kinetic mechanisms. Summarizing the behavior of all models tested with respect to burning velocities and NO formation in flames of methane and methanol, the mechanism of Glarborg et al. (2018) and the San Diego mechanism (2019) demonstrate uniformly satisfactory performance.
18.	Brackmann, Christian, et al. (author) Experimental studies of nitromethane flames and evaluation of kinetic mechanisms 2018 In: Combustion and Flame. - : Elsevier BV. - 0010-2180. ; 190, s. 327-336 Journal article (peer-reviewed)abstract The present work reports new experimental data for premixed flames of nitromethane, CH3NO2, at atmospheric pressure, and an evaluation of two contemporary kinetic mechanisms based on these new flame studies as well as previously published experimental data on laminar burning velocity and ignition. Flames of nitromethane + air at lean (ϕ = 0.8) and rich (ϕ = 1.2) conditions were stabilized on a flat-flame burner, where profiles of CH2O, CO and NO were obtained using laser-induced fluorescence and temperature profiles using coherent anti-Stokes Raman spectroscopy. Laminar burning velocities for nitromethane + O2 + CO2 were measured using the heat flux method for ϕ = 0.8–1.3 at 348 K and ϕ = 0.8–1.6 at 358 K, and an oxidizer composition of 35% O2 and 65% CO2. In addition, the effect of the oxidizer composition was examined for a stoichiometric flame at 358 K by varying oxygen fraction from 30% to 40%. The mechanism by Mathieu et al. (Fuel 2016, 182, 597), previously not validated for flames, was able to reproduce experimental laminar burning velocities for nitromethane + air, but under predicted new results for CH3NO2 + O2 + CO2 mixtures. The mechanism by Brequigny et al. (Proc. Combust. Inst. 2014, 35, 703) under predicted experimental laminar burning velocities significantly at all investigated conditions. Previous studies have shown that none of the mechanisms can accurately predict ignition delay time over a wide range of conditions with respect to pressure, temperature, diluent and dilution ratio. The evaluation of the mechanisms reveals that the understanding of nitromethane combustion is at the present time not sufficient to produce a widely applicable mechanism.
19.	Brackmann, Christian, et al. (author) Formation of NO and NH in NH3-doped CH4 + N2 + O2 flame : Experiments and modelling 2018 In: Combustion and Flame. - : Elsevier BV. - 0010-2180. ; 194, s. 278-284 Journal article (peer-reviewed)abstract Co-combustion of 5200 ppm NH3 with a stoichiometric, atmospheric pressure, CH4 + N2 + O2 flame has been investigated with experiments and kinetic modelling. Profiles of the amidogen (NH) radical and nitric oxide (NO) have been measured using laser-induced fluorescence, the latter being quantitatively determined. Temperature profiles were measured using Rayleigh scattering and thermocouple, the nonintrusive measurements were considered more reliable and were used for evaluation of LIF data as well as input for flame modelling. Experimental results are compared with predictions of a chemical mechanism developed by Mendiara and Glarborg (2009), with simulations based on solution of energy equation as well as on experimental temperature profiles as input. Compared with a neat flame, the NH3-doped flame shows a shift in position ∼0.7 mm downstream, as established from the measurements of the NH profile. Modelling prediction of post-flame NO concentrations in the NH3-doped flame, around 1160 ppm, was within the evaluated uncertainty with experimental data (1460 ppm). Reaction path analysis indicated NH2 as a key species in the formation of NO and N2 from the nitrogen added to the flame by NH3. Altogether, the mechanism predicts concentration levels rather well but fails to predict the shift in flame position obtained with addition of NH3 to the rather slowly burning hydrocarbon flame.
20.	Brackmann, Christian, et al. (author) Quantitative picosecond laser-induced fluorescence measurements of nitric oxide in flames 2017 In: Proceedings of the Combustion Institute. - : Elsevier BV. - 1540-7489. ; 36:3, s. 4533-4540 Journal article (peer-reviewed)abstract Quantitative concentrations measurements using time-resolved laser-induced fluorescence have been demonstrated for nitric oxide (NO) in flame. Fluorescence lifetimes measured using a picosecond Nd:YAG laser and optical parametric amplifier system have been used to directly compensate the measured signal for collisional quenching and evaluate NO concentration. The full evaluation also includes the spectral overlap between the ∼15cm-1 broad laser pulse and multiple NO absorption lines as well as the populations of the probed energy levels. Effective fluorescence lifetimes of 1.2 and 1.5ns were measured in prepared NO/N2/O2 mixtures at ambient pressure and temperature and in a premixed NH3-seeded CH4/N2/O2 flame, respectively. Concentrations evaluated from measurements in NO/N2/O2 mixtures with NO concentrations of 100-600ppm were in agreement with set values within 3% at higher concentrations. An accuracy of 13% was estimated by analysis of experimental uncertainties. An NO profile measured in the flame showed concentrations of ∼1000ppm in the post-flame region and is in good agreement with NO concentrations predicted by a chemical mechanism for NH3 combustion. An accuracy of 16% was estimated for the flame measurements. The direct concentration evaluation from time-resolved fluorescence allows for quantitative measurements in flames where the composition of major species and their collisional quenching on the probed species is unknown. In particular, this is valid for non-stationary turbulent combustion and implementation of the presented approach for measurements under such conditions is discussed.
21.	Capriolo, Gianluca, et al. (author) Combustion of propanol isomers : Experimental and kinetic modeling study 2020 In: Combustion and Flame. - : Elsevier BV. - 0010-2180. ; 218, s. 189-204 Journal article (peer-reviewed)abstract In this work an experimental and kinetic modeling study on n-propanol and i-propanol combustion has been performed. New burning velocity measurements were carried out using the heat flux method at 1 atm over the temperature range of 323–393 K. Analysis of the temperature dependence was conducted with to verify the data consistency of the new and available data from the literature. Important inconsistencies were identified with the literature experiments performed using the spherical flame method and the nature of such inconsistencies was discussed. Moreover, a new kinetic mechanism, based on the most recent Konnov model and extended to include C3 alcohol isomers chemistry subset, was validated against new and all available literature data obtained at different combustion regimes. Rate constant parameters were carefully selected by evaluating all experimental and theoretical sources. Moreover, Sarathy et al. (2014) detailed kinetic mechanism was also tested. Overall, both kinetic models reproduce experimental data with good fidelity, but the presented model was found superior in representing ignition delay times data performed at high-pressure conditions.
22.	Chen, Chenlin, et al. (author) Experimental and kinetic modeling study of laminar burning velocity enhancement by ozone additive in NH3+O2+N2 and NH3+CH4/C2H6/C3H8+air flames 2023 In: Proceedings of the Combustion Institute. - : Elsevier BV. - 1540-7489. ; 39:4, s. 4237-4246 Journal article (peer-reviewed)abstract Ammonia (NH3) is regarded as a promising future carbon-free fuel but needs to overcome drawbacks including extremely low burning velocity in practical combustion apparatus. In this study, ozone (O3) additive is used to elucidate one of the mechanisms of potential flame enhancement method based on plasma-assisted combustion. The effects of ozone addition on the laminar burning velocity of premixed NH3/(35%O2/65%N2) and NH3+ CH4/C2H6/C3H8+air flames over a wide range of equivalence ratios were investigated experimentally and numerically. Blending NH3 with hydrocarbons can decrease the ignition energy and increase the burning velocities of the whole mixture, which may contribute to developing ammonia co-fired mechanisms with varied complex fuels and validating the feasibility of NH3 using strategies in real applications. Measurements were conducted at atmospheric conditions using the Heat Flux method. For NH3/(35%O2/65%N2) flames, a significant increase was found on the fuel-lean side. Experimental data showed that maximum enhancement reaches 15.34% at π=0.6 with 5000 ppm O3 additive. For NH3+CH4/C2H6/C3H8+air blended flames, the enhancement effect was much more profound under off-stoichiometric conditions, being 1.5-4 times higher than that under near-stoichiometric conditions. A 28-step O3 related kinetic sub-mechanism was integrated with five selected NH3-oxidation mechanisms to simulate the burning velocities of NH3/(35%O2/65%N2) flames and CEU-Mech for NH3+CH4/C2H6/C3H8+air flames. Simulation results show improved agreement with the experimental data, especially for fuel-rich conditions as NH3 blending ratio xNH3 increases from 0 to 0.9. Each of the NH3/CH4/air, NH3/C2H6/air and NH3/C3H8/air cases fits well between experimental data and numerical results with varied NH3-fuel blending ratios. Detailed kinetic analyses adopting the CEU-NH3-Mech integrated with O3 sub-mechanism were carried out and revealed that active radicals such as HNO, which are rapidly produced due to high O concentration from O3 decomposing in the pre-heating zone, interfered with the ammonia-fuel chemistry and thus evidently promoted the overall combustion process.
23.	Chen, Jundie, et al. (author) An experimental and modeling study on the laminar burning velocities of ammonia + oxygen + argon mixtures 2023 In: Combustion and Flame. - 0010-2180. ; 255 Journal article (peer-reviewed)abstract Most often, the laminar burning velocity (SL) of ammonia was measured in mixtures diluted by nitrogen bearing in mind its potential use as an alternative carbon-free fuel. Replacing the diluent with argon can increase the flame temperature and thus provide additional targets for validating pertinent detailed kinetic models. The SL data for ammonia + oxygen + argon mixtures are scarce; therefore, in the present study, new measurements have been performed using the heat flux method at an initial temperature of 298 K and atmospheric pressure over an equivalence ratio range of 0.4–1.5. The argon mole percentage in the mixture has been changed from 30 to 60%. Nine recent ammonia kinetic models are selected and validated against these new experimental data, where it is found that the models by Han et al. (Combust. Flame 228 (2021):13), Shrestha et al. (Proc. Combust. Inst. 38 (2021):2163), and Okafor et al. (Combust. Flame 204 (2019):162) provide the best predictions. Further sensitivity analysis showed that the most crucial nitrogen-related reactions for SL in present flames found in the model of Shrestha et al. are different from the other two, and flux analysis elucidated that the main consumption fluxes of NH2 radical are different among the three models. The model of Han et al., which is from the authors’ group, was revisited, and the rate constants for three reactions NH2+H(+M)=NH3(+M), NNH+O[dbnd]NH+NO, and NH2+O[dbnd]HNO+H were modified. Available speciation data from shock tube and flame studies are used to select the most suitable rate constants among expressions recommended in the literature. The updated model performs well in reproducing a range of SL, ignition delay times, and speciation data from a jet-stirred reactor for ammonia + oxygen + argon mixtures.
24.	Christensen, Moah, et al. (author) Kinetics of premixed acetaldehyde plus air flames 2015 In: Proceedings of the Combustion Institute. - : Elsevier BV. - 1540-7489. ; 35, s. 499-506 Journal article (peer-reviewed)abstract Non-stretched laminar burning velocities, SL, of acetaldehyde + air mixtures at initial gas mixture temperatures, T, of 298, 318, 338, 348 and 358 K are reported for the first time. The flames were stabilized on a perforated plate burner at 1 atm using the heat flux method at conditions where the net heat loss from the flame to the burner is zero. Uncertainties of the measurements were analyzed and assessed experimentally. The overall accuracy of the burning velocities was estimated to be typically better than + 1 cm/s. Experimental results were compared with predictions of several kinetic models from the literature. Recent model of Leplat et al. (2011) [30] developed for acetaldehyde and ethanol oxidation showed the closest agreement with the measurements as compared to the Konnov and San Diego models. The effects of initial temperature on the adiabatic laminar burning velocities of acetaldehyde were interpreted using the correlation S-L = S-L0 (T/T-0)(alpha). Particular attention was paid to the variation of the power exponent alpha with equivalence ratio. The existence of a minimum in alpha in the slightly rich mixtures is demonstrated experimentally and confirmed computationally. The model of Leplat et al. was further analyzed using sensitivity analysis and it was concluded that the deviation of the modelled results when comparing with experiments is not a result of the fuel specific reactions but rather the sub-mechanisms of C1 and H-2/O-2. (C) 2014 The Combustion Institute. Published by Elsevier Inc. All rights reserved.
25.	Christensen, Moah, et al. (author) Laminar burning velocity of acetic acid + air flames 2016 In: Combustion and Flame. - : Elsevier BV. - 0010-2180. ; 170, s. 12-29 Journal article (peer-reviewed)abstract Laminar burning velocities of acetic acid + air flames at 1 atm and initial gas temperatures of 338 K, 348 K, and 358 K were determined using the heat flux method. Measurements were performed in non-stretched flames, stabilized on a perforated plate burner at adiabatic conditions. Due to experimental problems related to the corrosiveness of acetic acid towards the burner material, the uncertainty of the burning velocities was relatively high up to ± 2 cm/s. Seventy reactions pertinent to acetic acid and ketene have been reviewed and detailed reaction mechanism for acetic acid combustion was developed. The model over-predicts measured burning velocities by about 3 cm/s. The mechanism was also tested comparing with flame structure of the low-pressure flame of acetic acid (Leplat and Vandooren, 2012). Good agreement with the concentration profiles of major products was found, however several minor intermediates were over- or under-predicted by the model. To elucidate reactions responsible for the differences observed, the sensitivity analysis was performed. It was found that the calculated burning velocities are insensitive to the reactions of acetic acid and mostly governed by C1 chemistry typical for all hydrocarbons and by reactions of ketene. Possible modifications of the rate constants within the evaluated uncertainty factors were discussed.
26.	Christensen, Moah, et al. (author) Laminar burning velocity of diacetyl + air flames. Further assessment of combustion chemistry of ketene 2017 In: Combustion and Flame. - : Elsevier BV. - 0010-2180. ; 178, s. 97-110 Journal article (peer-reviewed)abstract Ketene is important intermediate in high-temperature chemistry of several oxygenates, such as acetone, acetic acid, and diacetyl. Ketene reactions appear in the sensitivity spectra of calculated burning velocities of the first two species. To provide independent experimental data for validation of the ketene sub-mechanism, the laminar burning velocities of diacetyl + air flames at 1 atm and initial gas temperatures of 298 K, 318 K, and 338 K were determined for the first time. Measurements were performed using the heat flux method in non-stretched flames, stabilised on a perforated plate burner at adiabatic conditions. Recently developed detailed kinetic mechanism for acetic acid flames with updated ketene sub-mechanism has been extended by reactions of diacetyl and includes revised rate constants for reactions of acetaldehyde and acetyl radical. The model was first compared with available experimental data on ketene pyrolysis and oxidation. Its performance in prediction of C2 species formation was improved by significant reduction of the previously estimated rate constants of ketene reactions with CH3 and CH2 radicals. The updated mechanism was then compared with the new measurements for diacetyl and earlier data for acetaldehyde, acetone and acetic acid flames. The model closely reproduces burning velocity of diacetyl + air in lean and rich mixtures while underpredicts in stoichiometric and slightly rich flames. Performance of the model for acetaldehyde + air flames was much improved as compared to the Konnov mechanism version 0.6. Good agreement of the modelling with experimental data for acetone + air flames was also demonstrated. The disparity between predicted burning velocities of acetic acid and recent measurements did not change. The model was further examined using sensitivity analysis for these flames to elucidate common reactions affecting its performance. It was concluded that the mechanism performance in prediction of the burning velocities of acetic acid flames could be improved by revision of reactions between CH2CO and OH radicals, while keeping its agreement with other flames studied. Remaining uncertainties in the ketene sub-mechanism are outlined.
27.	Dupont, Laurent, et al. (author) Experimental and kinetic modeling study of para-xylene chemistry in laminar premixed flames 2019 In: Fuel. - : Elsevier BV. - 0016-2361. ; 239, s. 814-829 Journal article (peer-reviewed)abstract The chemistry of para-xylene oxidation in laminar premixed flames has been analyzed using new experimental data on flame propagation at atmospheric pressure and flame structure of low-pressure stoichiometric flame. Atmospheric pressure laminar burning velocities of para-xylene + air flames were determined using the heat flux method at initial temperatures of 328 and 353 K over the equivalence ratio range of ϕ = 0.7–1.4 and of ϕ = 0.7–1.3, respectively. Temperature and mole fraction profiles of reactants, final products, and reactive and stable intermediate species have been measured in laminar premixed CH4/O2/N2 and CH4/1.5%C8H10/O2/N2 flames at low pressure (40 Torr) using thermocouple, molecular beam/mass spectrometry, and gas chromatography/mass spectrometry techniques. These new experimental results have been modeled with our previous model including sub-mechanisms for aromatics (benzene up to p-xylene) and aliphatic (C1 up to C7) oxidation. Good agreement has been observed for the profiles of the main species analyzed. Moreover, chemical pathways for common species in methane flame with and without 1.5% of benzene or 1.5% toluene investigated earlier under similar conditions were analysed and compared to the present flame doped with para-xylene. Key reactions of aromatics degradation in CH4/O2/N2 flames were identified and discussed. Burning velocities of para-xylene + air flames were also reproduced by the kinetic model.
28.	Han, Xinlu, et al. (author) A new correlation between diluent fraction and laminar burning velocities : Example of CH4, NH3, and CH4 + NH3 flames diluted by N2 2024 In: Fuel. - 0016-2361. ; 364 Journal article (peer-reviewed)abstract Modern combustion processes widely use exhaust gas recirculation, oxyfuel combustion, and other techniques that alter the concentration of diluent gases from that of the air. The dilution's impact on the laminar burning velocity, SL, is therefore a crucial effect that has been studied experimentally and numerically in the literature. However, an accurate fitting correlation with physical meanings is lacking, making it difficult to extrapolate SL data to real-application conditions. To address this gap, in the present work we have derived a novel correlation between diluent fraction and laminar burning velocity, SL, through new analysis of the maximum temperature gradient and heat release rate as lnSL/SL0=a1/Yu-1/Yu0, where Yu is the reactant mass fraction in the total unburnt mixture, and a being a constant when only the diluent concentration is varied. To provide data for the analysis and validation, SL of CH4 + O2 + N2, 40 %CH4 + 60 %NH3 + O2 + N2, and NH3 + O2 + N2 flames were measured using the heat flux method at varied oxygen ratio xO2 and equivalence ratio ϕ. Simulations were carried out using three kinetic mechanisms from Han, Konnov, and Okafor, which have been validated using both CH4 and NH3 burning velocities. Our experimental and simulation results for various fuel types and equivalence ratio conditions demonstrate good linearity with R2 > 0.985 over all ranges of xO2 spans, from the upper limit of xO2 = 1.0 to the lower limit where SL is below 5 cm/s, confirming the accuracy of the correlation equation. This correlation is also found valid under complex conditions with various unburned temperatures, pressures, diluent types, and fuel types, indicating its wide applicability. Sensitivity analyses revealed the kinetic origin of the linear lnSL vs. 1/Yu relationships. Specifically, the absolute values of a sensitivities are much smaller than those of SL, and they remain nearly the same for different oxygen ratios. Therefore, even by tuning the rate constants of the highly sensitive reactions, the a at different 1/Yu conditions will change uniformly, resulting in a linear lnSL vs. 1/Yu variation though with a different slope value.
29.	Han, Xinlu, et al. (author) A projection procedure to obtain adiabatic flames from non-adiabatic flames using heat flux method 2021 In: Proceedings of the Combustion Institute. - : Elsevier BV. - 1540-7489. ; 38:2, s. 2143-2151 Journal article (peer-reviewed)abstract Laminar burning velocity S L at elevated temperature T u and its temperature dependence coefficient α in SL/S0L = (Tu T0u)α are important parameters for industrial applications. However, experimental systems with high unburned gas temperatures may encounter pre-dissociation, leading to significant data scattering in the measurements. To negate this, the present work proposes a projection procedure to obtain adiabatic flame parameters at various unburned gas temperatures using non-adiabatic flames on a heat flux burner, by which the preheating can be achieved within much shorter time scale than, e.g., in conventional spherical flame methods, and the advantage of good data consistency in the heat flux method is kept. Burning velocity experiments were carried out with CH 4 + air atmospheric flames covering T u = 298-473 K, and the results show good agreement with the proposed projection equations. OH * spontaneous emission profiles were measured, indicating that the projection may extend to other flame characteristics. Uncertainty of the projection process was evaluated and comparisons were made with six popular kinetic mechanisms: GRI-Mech, FFCM-1 mech, Konnov mechanism, Glarborg mechanism, San Diego mechanism and Aramco mechanism. It is found that the simulated coefficients α are higher than experimental data especially at rich conditions; this is also found for literature values of high unburned gas temperature experiments. Possible reasons for this divergence are discussed.
30.	Han, Xinlu, et al. (author) An experimental and kinetic modeling study on the laminar burning velocity of NH3+N2O+air flames 2021 In: Combustion and Flame. - : Elsevier BV. - 0010-2180. ; 228, s. 13-28 Journal article (peer-reviewed)abstract In the present work, the laminar burning velocities of the NH3+N2O+air flames were measured using the heat flux method at 1 atm and 298 K, with varied equivalence ratios and N2O mixing ratios. For the mixing ratio N2O/(N2O+air) = 0.5, a full range of equivalence ratios was covered. Moreover, at three equivalence ratios an extended range of mixing ratios was investigated. The laminar burning velocity has an approximately linear relationship against the fraction of nitrous oxide in the oxidizer mixture, regardless of the tested equivalence ratios. Several recently published NH3 mechanisms were compared with these new experimental data; among them the models of Nakamura et al. and Stagni et al. show the best performance for NH3+N2O+air flames over the entire range of the mixing ratios. The H/N/O kinetic mechanism of the authors was analyzed and updated focusing on the rate constants of reactions most sensitive in ammonia flame propagation and self-ignition of NH3+O2 and H2+N2O mixtures. The choice of the new rate constants is outlined, however, no modification (adjustment or tuning) of the rate parameters to accommodate experimental results was attempted. The updated mechanism demonstrates significantly improved agreement with all measurements used for the model development and with other experimental data from the literature for ammonia flames and self-ignition. A comparative reaction path analysis for NH3+N2O+air and NH3+air flames revealed that an almost linear increase of the laminar burning velocity with an increased fraction of N2O in the oxidizer originates from the rate controlling reaction N2O+H = N2+OH, which produces OH radicals dominating ammonia oxidation.
31.	Han, Xinlu, et al. (author) Experimental and kinetic modeling study of NO formation in premixed CH4+O2+N2 flames 2021 In: Combustion and Flame. - : Elsevier BV. - 0010-2180. ; 223, s. 349-360 Journal article (peer-reviewed)abstract The nitric oxide (NO) formation in methane (CH4) flames has been widely investigated, with quite a few kinetic mechanisms available in the literature. However, studies have shown that there are often discrepancies between the simulations using various mechanisms and the experimental results. To elucidate reactions leading to these discrepancies, experiments were designed to measure the NO formation in the post flame zone of CH4+O2+N2 flames with the oxygen ratio, xO2 = O2/(O2+N2), varying from 0.2 to 0.27. The experiments were carried out on a heat flux burner at atmospheric pressure and 298 K using saturated Laser-induced fluorescence. The equivalence ratio, ϕ, was changed from 0.7 to 1.6. The corresponding laminar burning velocity, SL, for each condition was also measured using the heat flux method. A comparison was made for the present experimental data and simulation results using the Konnov, Glarborg, NOMecha 2.0, and San Diego mechanisms, and none of them well reproduced the new NO experimental data for all investigated conditions. Numerical analyses show that the increment of NO mole fraction in stoichiometric and fuel-lean flames when the xO2increases is mostly defined by the thermal-NO production, which is found to be over-predicted, especially by the Konnov and San Diego mechanisms. The rate constant of reaction NO+N = N2+O was derived as [Formula presented]cm3 / mol s over 225–2400 K temperature range. The rate constants of four reactions controlling CH mole fraction profiles and prompt-NO formation were updated based on the analysis of the literature data that yields an improved performance of the Konnov mechanism.
32.	Han, Xinlu, et al. (author) Experimental and kinetic modeling study of the CH4+H2S+air laminar burning velocities at atmospheric pressure 2022 In: Combustion and Flame. - : Elsevier BV. - 0010-2180. ; 244 Journal article (peer-reviewed)abstract With the increasing demand for natural gas and depletion of many sweet gas fields, direct usage of sour gas, usually containing a large percentage of hydrogen sulfide (H2S), becomes a more economical choice in recent years. However, the laminar burning velocity (SL) of CH4+H2S flames have seldom been investigated due to the corrosivity and toxicity of H2S, and no available experimental data can be found for these mixtures burnt in the air. In this work, the laminar burning velocities of CH4+H2S+air flames were measured using the heat flux method at 1 atm and 298 K. The experimental data were obtained at various equivalence ratios and xH2S = 0–0.25, where xH2S refers to the mole fraction of H2S in the fuel. Simulations using a detailed mechanism of Mulvihill et al. (2019) were carried out, showing good agreement with the present experimental results. Kinetic analyses of A-factor SL reaction sensitivities, reaction pathways, and dominant intermediate species pointed out the importance of the C- and S-containing species interactions. To overcome the convergence problem of the Mulvihill mechanism, an examination of the unphysical reactions and species was carried out, which could be alleviated by making several reactions that violate the collision limit irreversible, accompanied by updating the heat capacity data. It's also found that substituting the hydrocarbon subset of the Mulvihill mechanism with mechanisms from FFCM-1, Konnov, San Diego, as well as Aramco noticeably deteriorates the simulation results due to the selection of different reaction rate constants.
33.	Han, Xinlu, et al. (author) Over-rich combustion of CH4, C2H6, and C3H8 +air premixed flames investigated by the heat flux method and kinetic modeling 2019 In: Combustion and Flame. - : Elsevier BV. - 0010-2180. ; 210, s. 339-349 Journal article (peer-reviewed)abstract An uncommon non-monotonic behavior of the temperature dependence of adiabatic laminar burning velocity has been found in over-rich methane+air flames at equivalence ratio, ϕ = 1.4. To find out the universality and reasons of this turning point, methane, ethane and propane + air flames are studied both experimentally by the heat flux method and numerically using GRI-mech, USC-mech, UCSD-mech, FFCM mech, and Aramco mech over ϕ = 0.6–1.8, at unburned temperatures up to 368 K, and atmospheric pressure. Results show that the over-rich phenomena stem from a unique flame structure, where, after the flame front, H2O is reduced to H2 and C2Hx (x>1) is oxidized to CO, causing the temperature overtone (super adiabatic flame temperature), while some key reactions important for flame propagation changing their sensitivity signs. Inside the flame front, the importance of CH3 overwhelms other radicals like OH and H. By these distinguishing features, a method using temperature overtone to identify accurate turning points of over-rich regime is demonstrated.
34.	Han, Xinlu, et al. (author) Parametrization of the temperature dependence of laminar burning velocity for methane and ethane flames 2019 In: Fuel. - : Elsevier BV. - 0016-2361. ; 239, s. 1028-1037 Journal article (peer-reviewed)abstract The power exponent α in the temperature dependence of laminar burning velocity [Formula presented]=[Formula presented]α is usually considered an empirical parameter extracted from measurements performed at different temperatures. In this paper an analytical derivation of α is proposed, calculating the power exponent from the overall activation energy as: αTu 0→Tu =[Formula presented]·X+x. This relation is verified against experimental burning velocity data measured with the heat flux method and chemical kinetic models for flames with equivalence ratios, Φ, from 0.6 to 1.6 at up to 368 K unburned gas temperature and 1atm. Both methane and ethane were used as fuel. Laminar burning velocity predictions at elevated temperatures are made using proposed relation and the resulting values are in good agreement with existing data for methane flames up to 500 K. This indicates that the proposed mathematical derivation of α is accurate. In addition to providing a reliable extrapolation of the burning velocity at varying temperatures, isolating the temperature dependence of the power exponent α enables more accurate quantification of other factors, e.g., Φ, the unburned gas temperature and pressure, that influence laminar burning velocity. Additionally, it provides a simple means to evaluate the overall activation energy, Ea.
35.	Han, Xinlu, et al. (author) SAFT Regimes and Laminar Burning Velocities : A Comparative Study of NH3+ N2+ O2and CH4+ N2+ O2Flames 2023 In: Energy and Fuels. - 0887-0624. ; 37:11, s. 7958-7972 Journal article (peer-reviewed)abstract Super adiabatic flame temperature (SAFT) is a distinctive phenomenon in the adiabatic flame where the local maximum temperature exceeds the adiabatic flame temperature. The flame temperatures exhibiting the extent of SAFT are difficult to measure with low uncertainties in experiments, while the laminar burning velocity also represents global flame features, thus could possibly be related to the SAFT. The present study investigated the SAFT regimes, laminar burning velocities (SL), and their relationships for the CH4+ O2+ N2and NH3+ O2+ N2flames over large equivalence (φ) and oxygen ratio (xO2) ranges. The laminar burning velocities were experimentally measured using the heat flux method at φ = 1.4-1.8 and xO2= 0.22-0.44, where some conditions have never been reported before in the literature. Comparisons were made with simulated SLresults using five CH4mechanisms and five NH3mechanisms, and none of them well reproduce all of the experimental data. From the simulation results, three CH4SAFT regimes (I, II, and III) and two NH3SAFT regimes (I and II) have been identified, among which regime III for CH4and regime II for NH3were found for the first time. The kinetic origins of these regimes were discussed, and different flame features regarding the flame temperature and dominant species were clarified. The relationship between the SAFT extent and the laminar burning velocity is revealed by equation derivation based on the classical flame theories, proving that a mechanism reproducing well the SLand its temperature dependence can at the same time yield accurate predictions of the SAFT. The present study also provided the most sensitive reactions in the SAFT predictions accompanied by the rate constant uncertainties, which can be helpful for further mechanism development since none of the mechanisms reproduces well the present SLexperimental data, let alone the SAFT extent.
36.	Han, Xinlu, et al. (author) Temperature dependence of the laminar burning velocity for n-heptane and iso-octane/air flames 2020 In: Fuel. - : Elsevier BV. - 0016-2361. ; 276 Journal article (peer-reviewed)abstract The heat flux method is advantageous for obtaining adiabatic stretch-less flame and measuring laminar burning velocity, SL, with low uncertainty. However, its implementation is sometimes hampered by the instability, manifested as cellularity of the flame stabilized over a flat perforated burner. This paper summarizes the approaches of flame cellularity abatement on the heat flux burner, which are implemented in the present study for measuring burning velocities of n-heptane and iso-octane/air flames. The combination of approaches helped to effectively overcome the cellularity at the fuel-rich side of the tested flames, and the SL was measured at unburnt temperatures Tu=298K-358K and equivalence ratios ϕ=0.7-1.6, at atmospheric pressure, with the SL uncertainty being evaluated. Numerical simulations were carried out using LLNL mechanism, Chaos mechanism and Luong171 mechanism, and the results agree well with the experimental data. From the obtained experimental and numerical SL data, the temperature coefficients α in [Formula presented] as well as the overall activation energy, Ea, were derived. It was noted that for n-heptane and iso-octane/air flames, the tendencies of the α and Ea against ϕ resemble those for methane, ethane, and propane/air flames. Distinct over-rich flame structures were observed and discussed for n-heptane and iso-octane/air flames around ϕ≥1.5. Moreover, extrapolation proced/ure of the SLmeasurements was validated using analytical presentation of the heat flux method sensitivity, s vs. [Formula presented], and other parameters involved in the data processing, which may help to improve the accuracy of future experiments.
37.	Han, Xinlu, et al. (author) The temperature dependence of the laminar burning velocity and superadiabatic flame temperature phenomenon for NH3/air flames 2020 In: Combustion and Flame. - : Elsevier BV. - 0010-2180. ; 217, s. 314-320 Journal article (peer-reviewed)abstract Combustion of ammonia (NH3) as a carbon-free alternative fuel has been recently widely studied, with vast majority of the burning velocity data obtained at room temperature. In the present study, the laminar burning velocity SL of NH3/air mixtures has been measured at unburnt gas temperature Tu from 298 K to 448 K, covering equivalence ratios from 0.85 to 1.25 and at 1 atm using the heat flux method. Kinetic simulations were made with five literature mechanisms developed for NH3 combustion, i.e., Nakamura et al., Otomo et al., San Diego, Okafor et al., and Mei et al. mechanisms, and the influence of radiation heat losses was considered. Using the obtained burning velocity data at different temperatures, the temperature dependence coefficients α in [Formula presented] were derived, and compared with different models’ predictions. Further analyses of the temperature dependence of SL were carried out through examination of the overall activation energy, temperature and species profiles as well as the reaction paths, and a unique flame structure at the rich side of adiabatic NH3/air flames was found, which resembles ‘over-rich’ phenomena in hydrocarbon flames. At equivalence ratio larger than 1.1 ± 0.05, the NH3/air flames become so rich that (1) the NH2 radical overwhelms the H and OH radicals in maximum mole fraction; (2) after the flame front, H2O converts back to H2 with NO formed at the same time, causing the superadiabatic flame temperature phenomena, i.e. adiabatic flame temperature being lower than the maximum achieved in the flame. Moreover, local minimum NO concentration is found right after the over-rich NH3/air flame front, which may be helpful in reducing NO emissions from NH3 flames in practical applications.
38.	Han, Xinlu, et al. (author) Uniqueness and similarity in flame propagation of pre-dissociated NH3 + air and NH3 + H2 + air mixtures : An experimental and modelling study 2022 In: Fuel. - : Elsevier BV. - 0016-2361. ; 327 Journal article (peer-reviewed)abstract Ammonia (NH3) has attracted significant attention as a promising hydrogen carrier and a carbon-free alternative fuel. Partial dissociation could convert part of ammonia to H2 and N2 before injecting the fuel into a combustor, thus overcoming the low reactivity and high NOx emission problems during the NH3 combustion. The pre-dissociated NH3 + air mixture has unburnt species NH3, H2, O2, and N2, the same as more widely investigated NH3 + H2 + air flames, while similarities or differences between these two types of flames have not yet been investigated. In the present work, the laminar burning velocities of pre-dissociated NH3 + air flames at 1 atm and an initial temperature of 298 K have been measured and compared to the scarce data from the literature. Experiments were carried out using the heat flux method at varied dissociation ratio γ and equivalence ratio ϕ. Kinetic simulations were also performed using six recently published or updated mechanisms, while none of the tested mechanisms can accurately reproduce the present results for the pre-dissociated NH3 + air flames over the whole range of the covered conditions, even for those predicting well the NH3 + H2 + air flames. To understand this deficiency, flame temperatures for the two fuel systems were examined, as well as in-depth sensitivity analyses were carried out. Similar conditions between the pre-dissociated NH3 + air and the NH3 + H2 + air flames were found, and a new approach to identifying inconsistent experimental data obtained using the same experimental setup was also suggested and discussed.
39.	Johnson, Praise Noah, et al. (author) Oxidation kinetics of methyl crotonate : A comprehensive modeling and experimental study 2021 In: Combustion and Flame. - : Elsevier BV. - 0010-2180. ; 229 Journal article (peer-reviewed)abstract The current study explores the combustion behavior of methyl crotonate (CH3CH=CHC(=O)OCH3), which is a short ester representative of large unsaturated methyl esters. Starting with a detailed kinetic model for methyl butanoate (CH3CH2CH2C(=O)OCH3) oxidation, revisions are introduced to the C0-C4 chemistry based on the recent Aramco mechanism 3.0. The resulting mechanism is combined with a short model for methyl crotonate, derived from a suitable reference mechanism. Several new classes of reactions are included and the rate constants of the existing reactions are revised based on various theoretical studies and analogies to reactions of similar species. Furthermore, the low-temperature chemistry of methyl crotonate has been implemented in the current study to extend the validity of the mechanism to lower temperatures. The resulting methyl crotonate combustion mechanism has been comprehensively validated using various experiments in the literature. In addition, experiments are performed using a heat flux burner at atmospheric conditions to measure the laminar burning velocities of methyl crotonate at different unburnt mixture temperatures (318, 338, and 358 K). The mechanism is found to reproduce the experimental data for high-temperature combustion of methyl crotonate satisfactorily. The mechanism is also found to predict the low-temperature ignition delays accurately. Sensitivity and path flux analysis are performed to delineate the importance of the different reaction classes in methyl crotonate chemistry. The current study presents a comprehensive mechanism for methyl crotonate combustion, along with a new set of experimental results complementing the existing experimental database in the literature.
40.	Konnov, Alexander A., et al. (author) A comprehensive review of measurements and data analysis of laminar burning velocities for various fuel+air mixtures 2018 In: Progress in Energy and Combustion Science. - : Elsevier BV. - 0360-1285. ; 68, s. 197-267 Research review (peer-reviewed)abstract Accurate measurement and prediction of laminar burning velocity is important for characterization of premixed combustion properties of a fuel, development and validation of new kinetic models, and calibration of turbulent combustion models. Understanding the variation of laminar burning velocity with thermodynamic conditions is important from the perspective of practical applications in industrial furnaces, gas turbine combustors and rocket engines as operating temperatures and pressures are significantly higher than ambient conditions. With this perspective, a brief review of spherical flame propagation method, counterflow/stagnation burner method, heat-flux method, annular stepwise method, externally heated diverging channel method, and Bunsen method is presented. A direct comparison of power exponents for temperature (α) and pressure (β) obtained from different experiments and derived from various kinetic mechanisms is reported to provide an independent tool for detailed validation of kinetic schemes. Accurate prediction of laminar burning velocities at higher temperatures and pressures for individual fuels will help in closer scrutiny of the existing experimental data for various uncertainties due to inherent challenges in individual measurement techniques. Laminar burning velocity data for hydrogen (H2), gaseous alkane fuels (methane, ethane, propane, n-butane, n-pentane), liquid alkane fuels (n-heptane, isooctane, n-decane), alcohols (CH3OH, C2H5OH, n-propanol, n-butanol, n-pentanol) and di-methyl ether (DME) are obtained from literature of last three decades for a wide range of pressures (1–10 bar), temperatures (300–700 K), equivalence ratios and mixture dilutions. The available experimental and numerical data for H2 and methane fuels compares well for various pressures and temperatures. However, more experimental and kinetic model development studies are required for other fuels. Comparison of laminar burning velocity data obtained from different measurement techniques at higher initial pressures and temperatures showed significant deviations for all fuels. This suggests to conduct focused measurements at elevated pressure and temperature conditions for different fuels to enable the development of accurate kinetic models for wider range of mixtures and thermodynamic conditions.
41.	Konnov, Alexander A. (author) An exploratory modelling study of chemiluminescence in ammonia-fuelled flames. Part 1 2023 In: Combustion and Flame. - 0010-2180. ; 253 Journal article (peer-reviewed)abstract The present exploratory study is aimed at the modelling of the chemiluminescence signature of premixed laminar NH3+H2+air flames. The detailed kinetic mechanism of the author was extended by reactions describing the formation and consumption of excited NO2, NO(A), NH, and NH2* mostly relying on previous analyses of chemiluminescence processes from the literature. The lowest-lying excited state of molecular nitrogen, N2(A) is also invoked to analyse its possible impact on the formation of these emitting species. In the present model, the formation of NO(A) and NH* in NH3+H2+air flames is governed by the energy transfer from N2(A) to the ground state NO and NH, respectively. The new model predictions are compared with available experimental data obtained by Zhu et al. in laminar counterflow NH3+H2+air flames (PROCI 39 (2023)). Good agreement with the measurements was demonstrated for NO(A), OH, and NH, both in terms of their variation with equivalence ratio and the amounts of ammonia in the fuel. Moreover, the model qualitatively captures the ratios of chemiluminescence intensity of OH/NO(A), NH/OH* and NH/NO(A). Further analysis revealed that the bimodal behaviour of chemiluminescence in the spectral regions identified by Zhu et al. as “blue”, “green”, “yellow”, “orange”, and “red”, can be explained by the interplay of emissions from NO2 and NH2, while emission in the “violet” spectral band could be assigned to excited H2O.
42.	Konnov, Alexander A. (author) An exploratory modelling study of chemiluminescence in ammonia-fuelled flames. Part 2 2023 In: Combustion and Flame. - 0010-2180. ; 253 Journal article (peer-reviewed)abstract The detailed kinetic mechanism of the author was extended by reactions describing formation and consumption of excited species which are formed in NH3+CH4+air flames, complementing the modelling efforts presented in Part 1. Currently the model includes the following excited species: O(1D), OH, O2, CH, CH2(1), NO2, NO(A), NH, N2(A), NH2, C2, CO2, CH2O, and CN, among which many were observed in chemiluminescence signatures of ammonia-fuelled flames. The new model predictions were compared with the experimental data obtained in laminar premixed counterflow NH3+CH4+air flames (Combust. Flame 231 (2021) 111508). The overall agreement between the measurements and calculations was not as good as it was observed for NO(A), OH* and NH* in NH3+H2+air flames presented in Part 1. It was argued that both unquantified experimental uncertainties and remaining deficiencies of the model could contribute to the discrepancies found. Nevertheless, for OH, NH, CN, CO2 and CH*, as well as for several ratios of chemiluminescence intensity of different excited species the predicted trends both in terms of their variation with equivalence ratio and the amounts of ammonia in the fuel are in qualitative agreement with the measurements. The most important inconsistency between the experiments and modelling is found for NO(A), which is the only species in NH3+CH4+air flames forming, according to the present mechanism, by the energy transfer from N2(A). This indicates that either formation of N2(A) precursors, namely NH and N, is not accurate due to missing interaction of nitrogen and hydrocarbon chemistry, or reactive quenching of N2(A) is incomplete and requires further development.
43.	Konnov, Alexander A., et al. (author) Combustion chemistry of methoxymethanol. Part II : Laminar flames of methanol+formaldehyde fuel mixtures 2021 In: Combustion and Flame. - : Elsevier BV. - 0010-2180. ; 229 Journal article (peer-reviewed)abstract In the present study, the laminar burning velocities of mixtures of up to 16.4% (mol) formaldehyde in methanol, burning with air, were determined at atmospheric pressure using the heat flux method covering lean, stoichiometric and rich flames at initial gas mixture temperatures of 298, 318 and 338 K. Results published in the literature indicate that evaporation of CH2O+CH3OH fuel blends should lead to a gaseous mixture of formaldehyde, methanol and methoxymethanol, although the composition of these components in the gas phase was not well defined. To interpret the measurements performed in the present study, the detailed kinetic model developed by the group of Konnov was used. The recently updated mechanism was further extended by the reactions of methoxymethanol with the rate constants calculated in Part I of the present study. A comparison of the predictions of this mechanism with the new experimental data indicated that between 40% and 60% of CH2O present in the investigated CH2O+CH3OH mixtures were at 473 K evaporated as gaseous formaldehyde monomer, while the rest was released within CH3OCH2OH. Laminar burning velocity results suggest partial condensation of methoxymethanol in the CH3OH+CH2O fuel mixture with 5.84% formaldehyde at rich conditions and 298 K. These observations allowed evaluation of the partial pressure of CH3OCH2OH which was found to be between 0.35 and 0.52 kPa. The sensitivity and rate-of-production analyses revealed that the reduced reactivity with the increased amount of methoxymethanol in the fuel mixtures is explained by the conversion of CH3OCH2OH to CH3OCHOH radicals due to favored H-abstraction from the secondary hydrogen atoms predicted by ab initio calculations compared to other sites of methoxymethanol. Hydroxyl-methoxyl-methyl radicals further decompose forming slowly reacting formic acid and methyl radicals.
44.	Konnov, Alexander A., et al. (author) Laminar burning velocities of cyclopropane flames 2022 In: Combustion and Flame. - : Elsevier BV. - 0010-2180. ; 246 Journal article (peer-reviewed)abstract Cyclopropane, c-C3H6, the simplest cycloalkane, is seldom included in detailed kinetic mechanisms for hydrocarbons, though it may exhibit unusual kinetic features yet to be analysed due to a lack of studies of its combustion characteristics. In this work, laminar burning velocities of cyclopropane flames have been determined using the heat flux method at atmospheric pressure and an initial gas mixture temperature of 298 K. The fuel consisting of 50% c-C3H6 + 50% N2 was burnt with air covering the range of equivalence ratios 0.6 – 1.5. The detailed kinetic model of the authors was extended by the reactions of cyclopropane and cyclopropyl radical, c-C3H5, with the rate constants selected from the literature. This mechanism, as well as the most recent mechanisms for c-C3H6 of Wang et al. (2022) and of Lei et al. (2022), have been compared with the burning velocities of propylene + air flames and with the new experimental results for cyclopropane flames. The model of Lei et al. (2022) significantly underpredicts the burning velocities for both fuels, on the other hand, good agreement with predictions of the present model and of Wang et al. (2022) was observed at 1 atm. However, further sensitivity and rate-of-production analyses revealed important differences in the pathways of c-C3H6 oxidation predicted by the two mechanisms. The present kinetic model was also tested using all available measurements of cyclopropane ignition delays in shock tubes, which combined cover the range of equivalence ratios from 0.33 to 3, at pressures 1 - 10 atm, and temperatures 1100 – 2100 K. Overall good performance of the model was demonstrated across these ranges of conditions and compositions of the mixture. A direct comparison of the experimental data shows that ignition delays of propylene are slightly longer than those of cyclopropane, yet in most cases within the overlapping uncertainties or scattering between different experimental facilities. The laminar burning velocities of c-C3H6 + air are slightly higher than those of C3H6 + air at least according to the predictions of the present mechanism and the model of Wang et al. (2022).
45.	Konnov, Alexander A., et al. (author) Measurements of the laminar burning velocities of small alkyl esters using the heat flux method : A comparative study 2023 In: Combustion and Flame. - 0010-2180. ; 255 Journal article (peer-reviewed)abstract Consistent datasets of the laminar burning velocity, LBV, for homologous fuels are indispensable for the elucidation of the structure-reactivity trends and the development and validation of pertinent detailed kinetic models. In the present study, all available LBV measurements for small alkyl esters obtained using the heat flux method have been reviewed. New results of the LBV for methyl propionate + air flames employing this method have been acquired at atmospheric pressure and initial gas temperatures from 298 to 348 K over equivalence ratios, ɸ = 0.7–1.5. Earlier experimental data for alkyl esters scattered across non-archival reports were re-examined and corrected when necessary. To prove the validity of the correction, additional LBV measurements for methyl formate and methyl butanoate were performed as well, and successfully demonstrated the consistency of the data obtained using different installations over an extended period of time. Then, the LBV of different families, such as methyl esters of various acids, formates, and acetates, along with isomers, were compared and structure-reactivity trends were assessed. Furthermore, the detailed kinetic mechanism of the authors was expanded by the reactions of methyl propionate and successfully compared with the LBV measurements for methyl formate, methyl acetate, methyl propionate, and ethyl formate. Distinct reactions controlling their flame propagation were revealed using sensitivity analysis and the origin of their rate constants is briefly discussed.
46.	Konnov, Alexander A. (author) Yet another kinetic mechanism for hydrogen combustion 2019 In: Combustion and Flame. - : Elsevier BV. - 0010-2180. ; 203, s. 14-22 Journal article (peer-reviewed)abstract Recent suggestion by Burke and Klippenstein (2017) that chemically termolecular reactions H + O2 + R may significantly affect kinetic pathways under common combustion situations requires careful analysis, since, if included in contemporary kinetic mechanisms, these reactions affect global reactivity and calculated burning velocities of laminar premixed flames. In the view of their impact, a detailed kinetic scheme for hydrogen combustion was revisited to elucidate how to counterbalance enhanced chain termination caused by chemically termolecular reactions in attempt to keep or improve model performance. First, recent experimental and theoretical kinetic studies of hydrogen reactions were analyzed. In the new mechanism four reactions were introduced and three rate constants were updated. These changes, however, significantly reduce calculated burning velocities of H2 + air flames as compared to experimental data and earlier model predictions with the major impact from chemically termolecular reactions. It was then found that implementation of the new theoretical transport database developed by Jasper et al. (2014) significantly improves the performance of the updated kinetic model. The new kinetic mechanism for hydrogen combustion which includes updated kinetics and new transport properties was found in good agreement with the consistent dataset of the burning velocity measurements for hydrogen flames obtained using the heat flux method at atmospheric pressure for which the behavior of the previous model of the author was not satisfactory.
47.	Lavadera, Marco Lubrano, et al. (author) Experimental and modeling study of laminar burning velocities and nitric oxide formation in premixed ethylene/air flames 2021 In: Proceedings of the Combustion Institute. - : Elsevier BV. - 1540-7489. ; 38:1, s. 395-404 Journal article (peer-reviewed)abstract Adiabatic laminar burning velocities and post-flame NO concentrations for flat, non-stretched, premixed C2 H 4 /air flames were experimentally determined with a heat flux burner of improved design, over equivalence ratios ranging from 0.7 to 2, at atmospheric pressure and initial temperature of 298 K. Recognizing that C2 H 4 is a main intermediate in high-temperature oxidation pathways of heavy hydrocarbons, these data are essential for the development, validation and optimization of kinetic models for any fuel. The present measurements were then compared with the data available in the literature obtained with different techniques under the same experimental conditions. Regarding burning velocity measurements, the comparison showed considerable scatter among existing stretch-corrected data, which corroborate the necessity for the present adiabatic, non-stretched results. Regarding NO concentrations, an excellent agreement was observed between the present in situ, non-intrusive laser-induced fluorescence measurements and the only dataset available in the literature, determined by the phenol disulfonic acid method. A comparison of experimental and computational results using two contemporary comprehensive, detailed chemical kinetic mechanisms, along with one from the authors presented in this work, was also conducted and discussed. Discrepancies between experiments and model predictions and among models themselves were observed under rich conditions. Notwithstanding, the present updated model showed overall good performances in reproducing both laminar burning velocities and nitric oxide concentrations. Further numerical analyses were performed to identify the main causes of the observed differences. The results showed that the description of the relative importance of reactions involving vinyl and hydrogen cyanide consumption pathways, due to remaining uncertainties, lead to the different model behaviors.
48.	Li, Rui, et al. (author) Chemical mechanism development and reduction for combustion of NH3/H2/CH4 mixtures 2019 In: Fuel. - : Elsevier BV. - 0016-2361. ; 257 Journal article (peer-reviewed)abstract To achieve a reduced chemical model for comprehensive prediction of ammonia/hydrogen/methane mixture combustion, a detailed chemical mechanism with 128 species and 957 reactions was first assembled using models from literature. Directed relation graph with error propagation (DRGEP) with sensitivity analysis reduction method was then used to obtain compact reaction models. The studied reduction conditions cover ɸ = 0.5–2.0, temperature 1000–2000 K, and pressure 0.1–5 MPa. Finally, two reduced models have been obtained: 28 species and 213 reactions for ammonia/hydrogen and 51 species and 420 reactions for ammonia/hydrogen/methane. Ignition delay times and laminar burning velocities for single component and fuel mixtures predicted using the detailed and reduced mechanisms were compared with available experiments. Results showed that both detailed and reduced mechanisms performed fairly well for ignition delays, while over-predicted laminar burning velocity at fuel-rich conditions for single ammonia fuel and mixtures. The 51 species reduced mechanism was also tested in non-premixed coflow hydrogen/methane jet flames, while 1%–50% mole ammonia were added to the fuel stream. Modelling results showed that this 51-species mechanism was suitable for CFD modelling, and the speedup factor was over 5 when using the reduced mechanism with different codes. The flame structure, as well as NO and NO2 formation was studied. High NO concentrations were found in high-temperature region near the stoichiometric zone, while NO2 was dominant in the lean flame zone. Reaction flux analysis was performed to better understand NH3 oxidation and NOx emissions at low- and high-temperature conditions.
49.	Li, Rui, et al. (author) Comparative analysis of detailed and reduced kinetic models for CH 4 + H 2 combustion 2019 In: Fuel. - : Elsevier BV. - 0016-2361. ; 246, s. 244-258 Journal article (peer-reviewed)abstract Directed relation graph with error propagation (DRGEP) method combined with extensive validation for 0D, 1D and 2D CFD modeling supported by sensitivity and Rate-Of-Production (ROP) analyses are implemented for comparative study of detailed and reduced kinetic mechanisms for CH 4 + H 2 combustion. To this end, two detailed kinetic mechanisms, namely AramcoMech 2.0 and recently updated Konnov mechanism, were validated using available measurements of ignition delay times and laminar burning velocities for hydrogen, methane and hydrogen + methane fuel mixtures. For all experimental conditions visited, both detailed mechanisms demonstrated good and close to each other performance. Two-stage DRGEP method and reaction reduction based on computational singular perturbation (CSP) were then implemented to achieve two skeletal models: 25 species and 105 reactions for AramcoMech 2.0 and 27 species and 107 reactions for the Konnov model. The conditions for skeletal models generation cover ɸ = 0.5–2.0, temperature 900–2000 K, and pressure 1–50 bar. Turbulent non-premixed flames of CH 4 + H 2 in the Jet in Hot Co-flow (JHC) burner for two different oxygen concentrations in a co-flow were modeled using both skeletal models. 2-D RANS simulations with OpenFOAM code of the flame structure using the two skeletal kinetic mechanisms are similar except for the mass fraction of OH and CO. To elucidate the differences between two skeletal mechanisms generated using the same reduction method, extensive validation for 0D, 1D and 2D CFD modeling were supported by sensitivity analysis for detailed and skeletal reaction models. Good agreement between the skeletal and detailed mechanisms was found in top reactions as well as their sensitivity coefficients, which affect auto-ignition process and laminar flame propagation. Further chemical and sensitivity analysis of the structure of laminar flames demonstrate that three important reactions, i.e. CO + OH = CO 2 + H, H 2 + OH = H + H 2 O, and CH 4 + OH = CH 3 + H 2 O have different rate constants in the Aramco and Konnov models that may contribute to the differences in the prediction of CO concentration profiles. The simulation predictions for CO concentrations are improved for laminar flames and JHC flame by using a 25-species modified version in which these rate constants were taken from the Konnov mechanism. It was noted that DRGEP method applied to different detailed kinetic schemes generate skeletal models with different, non-overlapping lists of retained species. The presence of CH 2 CHO in the Aramco 25-species skeletal mechanism and its absence in the Konnov 27-species mechanism, and the presence of CH, CH 2 , CH 2 CO in the latter and their absence in the former mechanism were analysed and explained using Rate-Of-Production analysis for conditions found in the CFD simulations.
50.	Lin, Qianjin, et al. (author) Measurements of laminar burning velocities and an improved kinetic model of methyl isopropyl ketone 2023 In: Combustion and Flame. - 0010-2180. ; 258 Journal article (peer-reviewed)abstract Methyl isopropyl ketone (MIPK) is the simplest branched ketone and a promising biofuel. In this work, laminar burning velocities (SL) of MIPK + air flames were measured using the heat flux method at atmospheric pressure, over initial mixture temperatures of 298–358 K and equivalence ratios of 0.7–1.4. With the help of the temperature dependence of the SL, data inconsistency between the present measurements and the experimental data reported by Li et al. (Proc. Combust. Inst. 38 (2021) 2135) was demonstrated. Moreover, existing kinetic models for MIPK combustion notably deviate from the present SL measurements. Therefore, the MIPK model suggested by Lin et al. (Proc. Combust. Inst. 39 (2023) 315) was updated by revisiting the MIPK H-abstraction reactions and methyl isopropenyl ketone sub-model. Furthermore, a new di-methyl ketene (critical intermediate during MIPK oxidation) sub-model was constructed and integrated into the MIPK model. Flux and sensitivity analyses revealed that integration of the new di-methyl ketene model improves predictions of the laminar burning velocities as well as shock tube ignition delay times over the pressures of 1–40 bar due to converting di-methyl ketene into C3H5-T (CH2 = C˙CH3) rather than C3H6 or C3H5-S (C˙H = CHCH3) predicted by other MIPK models from the literature. Updates of the MIPK H-abstraction reactions yield more reasonable products branching ratios of formation of the primary fuel radicals, and improve prediction of the SL. It was also found that the rate constants of the MIPK decomposition reaction (MIPK (+M) = CH3CO + IC3H7 (+M)) in the model proposed by Li et al. (Proc. Combust. Inst. 38 (2021) 2135) are significantly underestimated, resulting in underestimation of the present SL measurements and significant overprediction of the ignition delay times.

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Author/Editor: Konnov, Alexander A. (73); Han, Xinlu (14); Lubrano Lavadera, Ma ... (13); Brackmann, Christian (11); Wang, Zhihua (11); Nilsson, Elna J.K. (10); show more...; He, Yong (10); Pitz, William J. (7); Alekseev, Vladimir A ... (6); Capriolo, Gianluca (6); Zhu, Yanqun (6); Wagnon, Scott W. (5); Curran, Henry J. (5); Chen, Jundie (5); Zhou, Chong Wen (5); Serinyel, Zeynep (5); Dayma, Guillaume (5); Wang, Shixing (5); Mehl, Marco (4); Lokachari, Nitin (4); Matveev, Sergey S. (4); Matveev, Sergey G. (4); Christensen, Moah (4); Konnov, Alexander (4); Dagaut, Philippe (4); Aldén, Marcus (3); Roberts, William L. (3); Kim, Seonah (3); Chechet, Ivan V. (3); Heimdal Nilsson, Eln ... (3); Nauclér, Jenny D. (3); Li, Rui (3); Zhu, Yuxiang (3); Lin, Riyi (3); Liu, Yingzu (3); Qin, Fei (3); Lavadera, Marco Lubr ... (3); Larfeldt, Jenny (2); Ahmed, Ahfaz (2); Bai, Xue-Song (2); Methling, Torsten (2); Jangi, Mehdi (2); Knyazkov, Denis A. (2); Korobeinichev, Oleg ... (2); Narayanaswamy, Krith ... (2); He, Guoqiang (2); Mebel, Alexander M. (2); Kukkadapu, Goutham (2); Song, Hwasup (2); Vanhove, Guillaume (2); show less...

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