| 1. |
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| 2. |
- Alekseev, Vladimir A., et al.
(författare)
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Data consistency of the burning velocity measurements using the heat flux method : Hydrogen flames
- 2018
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Ingår i: Combustion and Flame. - : Elsevier BV. - 0010-2180. ; 194, s. 28-36
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Tidskriftsartikel (refereegranskat)abstract
- Consistent datasets of experiments are highly important both for validation and optimization of kinetic mechanisms. An analysis of the data consistency of all available burning velocity measurements of hydrogen flames using the heat flux method at atmospheric pressure is performed in the present work. A comparison of many experiments performed in several laboratories with different types of dilution by various inerts was guided by kinetic modeling using two kinetic mechanisms. Konnov (2015) and ELTE (Varga et al., 2016) models demonstrated a uniform trend at all conditions tested: the second mechanism predicts lower burning velocities which are in better agreement with the heat flux measurements from different groups. Some experimental datasets, however, significantly disagree with one or both models; these conditions were revisited experimentally in the present work. The laminar burning velocities of H2 + O2 + N2 mixtures with 7.7% O2 in O2 + N2 oxidizer and of 85:15 (H2 + N2) and 25:75 (H2 + N2) fuel mixtures with 12.5:87.5 (O2 + He) oxidizer have been measured. It was concluded that the results of Hermanns et al. (2007) are somewhat higher than those of other studies at similar conditions and a possible reason of this disagreement was suggested. Analysis of the measurements performed by Goswami et al. (2015) on a high-pressure installation suggests an equipment malfunction that led to the erroneous values of the equivalence ratio for hydrogen and syngas flames. The ELTE mechanism developed using an optimization approach shows a very good performance in predicting laminar burning velocities of hydrogen flames measured using the heat flux method.
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| 3. |
- Alekseev, Vladimir A., et al.
(författare)
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High-temperature oxidation of acetylene by N2O at high Ar dilution conditions and in laminar premixed C2H2 + O2 + N2 flames
- 2022
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Ingår i: Combustion and Flame. - : Elsevier BV. - 0010-2180. ; 238
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Tidskriftsartikel (refereegranskat)abstract
- High-temperature oxidation of acetylene (C2H2) is studied behind reflected shock waves and in laminar flames. Atomic resonance absorption spectroscopy (ARAS) is employed to record oxygen atom concentration profiles for the mixture of 10 ppm C2H2 + 10 ppm N2O + argon and temperatures from 1688 K to 3179 K, extending the range of such data available from the literature. Laminar burning velocity of C2H2 in a diluted oxidizer with 11–13% O2 in the O2 + N2 mixture is measured using the heat flux method and compared to the literature data for the 13% O2 mixture. An updated detailed kinetic mechanism is presented to model and analyze the results, and the selection of rate constants in the C2H2 sub-mechanism, whose importance was identified by the sensitivity analysis, is discussed. The performance of the new model is compared against several reaction schemes available from the literature, and kinetic differences between them are outlined. The new shock-wave data helped to improve the performance of the present model compared to its previous version. For the laminar flames, a particular importance of reactions involving C2H3 is identified, however, the reasons for the observed differences in model predictions are to a large extent located outside the C2H2 sub-mechanism, which were also identified.
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| 4. |
- Alekseev, Vladimir A., et al.
(författare)
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Laminar burning velocities of methylcyclohexane + air flames at room and elevated temperatures : A comparative study
- 2018
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Ingår i: Combustion and Flame. - : Elsevier BV. - 0010-2180. ; 196, s. 99-107
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Tidskriftsartikel (refereegranskat)abstract
- Laminar burning velocities of methylcyclohexane + air flames were determined using the heat flux method at atmospheric pressure and initial temperatures of 298–400 K. The measurements were performed on two experimental setups at Lund University and Samara National Research University. Our results obtained at the same initial temperatures are in good agreement. Consistency of the measurements performed at different temperatures was tested employing analysis of the temperature dependence of the burning velocities. This analysis revealed increased scatter in the burning velocity data at some equivalence ratios which may be attributed to the differences in the design of the burners used. New measurements were also compared to available literature data. Reasonably good agreement with the data of Kumar and Sung (2010) was observed at 400 K, with significantly higher burning velocities at the maximum at 353 K as compared to other studies from the literature. Predictions of two detailed reaction mechanisms developed for jet fuels – PoliMi and JetSurF 2.0 were compared with the present generally consistent measurements. The two kinetic models disagreed with each other, with the experimental data being located in between the model predictions. Sensitivity analysis revealed that behavior of the models is largely defined by C0–C2 chemistry. Comparison of the model predictions with the burning velocities of ethylene and methane showed the same trends in over- and under-predictions as for methylcyclohexane + air flames.
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| 5. |
- Alekseev, Vladimir A., et al.
(författare)
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Nitric oxide formation in flames of NH3/DME binary mixtures : Laser-induced fluorescence measurements and detailed kinetic analysis
- 2024
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Ingår i: Fuel. - 0016-2361. ; 371
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Tidskriftsartikel (refereegranskat)abstract
- Binary mixture of ammonia (NH3) and dimethyl ether (DME) has been considered in literature as a potential fuel for practical use. Nitric oxide (NO) is a major product of combustion of NH3-containing fuels, and its formation routes have to be comprehensively studied. In this work, concentration profiles of NO were experimentally measured in laminar axisymmetric flames using planar laser-induced fluorescence. The molar percentage of NH3 in the NH3/DME fuel mixture varied from 10% to 60%. Emission levels of NO have reached as much as around 1% for mixtures with around 50% NH3. NO formation was analyzed with numerical simulations of 1D laminar flames and several detailed kinetic mechanisms. Modeling was performed in Chemkin with the steady-state burner-stabilized and free-propagating planar laminar flame reactor models. It was observed that the most recent versions of the contemporary NH3/DME models are able to reproduce the experiments, and their predictions agree with each other due to similarities in the NH3 submechanisms. Kinetic analysis has revealed some disagreement was observed in terms of how much direct chemical coupling between carbon- and nitrogen-containing species affects NO formation.
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| 6. |
- Alekseev, Vladimir A., et al.
(författare)
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Reduced kinetics of NH3/n-heptane : Model analysis and a new small mechanism for engine applications
- 2024
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Ingår i: Fuel. - 0016-2361. ; 367
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Tidskriftsartikel (refereegranskat)abstract
- A compact reduced mechanism covering a wide range of conditions is developed for use in simulations of NH3/n-heptane combustion in engines. Reduction targets were selected after reviewing available experimental studies of NH3 combustion in engines. Ignition, flames and oxidation of NH3/n-heptane mixtures were targeted. Particularly, mixtures with very low molar percentage of n-heptane which are important for the applications were considered. They have been observed to have a distinct ignition behavior. Target quantities also included pollutants with a goal to account for two possible mechanisms of N2O formation in engines, discussed in literature. The reduced mechanism of this study was developed with ant colony reduction method. It consists of 57 species and 159 reactions, and its range of applicability is 10–100 atm pressure and 0–100 % NH3 in the fuel mixture. The performance of the mechanism was found comparable to larger models from literature. Importance of carbon–nitrogen interactions, influence of key reactions in the NH3 subset and effect of CO on N2O formation were analyzed and discussed in terms of the predictive ability of the reduced mechanism of the present study and those available from literature.
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| 7. |
- Alekseev, Vladimir, et al.
(författare)
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Experimental Uncertainties of the Heat Flux Method for Measuring Burning Velocities
- 2016
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Ingår i: Combustion Science and Technology. - : Informa UK Limited. - 1563-521X .- 0010-2202. ; 188:6, s. 853-894
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Tidskriftsartikel (refereegranskat)abstract
- The laminar burning velocity is a fundamental property of combustiblemixtures important for kinetic model validation as well as for practicalapplications. Many efforts are directed towards its accurate determination.The heat flux method is one of the commonly recognized methodsfor measuring laminar burning velocity, however, the information on theaccuracy of the method is scattered in the literature. In the present work,an attempt wasmade to summarize and extend the available informationon the different factors contributing to the experimental uncertainty ofthe heat flux method. Experimental setup of the Lund University group,typical for the heat flux community, and the procedures used to determinethe burning velocity are described. Furthermore, the influence ofdifferent uncertainty factors, originating from each part of the setup, isanalyzed. Asymmetric heat fluxes and the method for determining flamesurface area were found to give an important contribution to the totalerror. As a result of this, some of the previously published data have beenre-evaluated. Finally, recommendations are presented on how to controlor reduce the uncertainties in the heat flux measurements, and possibledirections for future research, aimed at improvement of the accuracy andunderstanding of the method, are outlined.
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| 8. |
- Alekseev, Vladimir
(författare)
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Laminar burning velocity of hydrogen and flame structure of related fuels for detailed kinetic model validation
- 2015
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The laminar burning velocity and the flame structure are common targets for combustion studies aimed at detailed kinetic model development. In the present work, fuels relevant to hydrogen combustion were considered. The laminar burning velocity of rich and lean hydrogen flames was studied experimentally and numerically, including its pressure dependence in rich mixtures and temperature dependence in lean mixtures. An updated version of the Konnov detailed reaction mechanism for H2 combustion was validated, and after that it was applied to simulate the results obtained in experiments. The laminar burning velocities of rich H2 + air mixtures were determined from spherical flame propagation data using three models for stretch correction available in the literature. The heat flux method was employed for the first time to measure the laminar burning velocity of lean H2 + air mixtures and its temperature dependence. A modified procedure for processing data from unstable cellular flames was suggested, and its accuracy was evaluated. The observed difference between the literature results obtained in stretched flames and the values measured in the present work in flat flames was discussed. The trends in the temperature dependence of the burning velocity of lean H2 + air mixtures, indicated by the modeling but not supported by the majority of data determined from literature values, were confirmed experimentally in the present work. An analysis of the experimental uncertainties of the heat flux method was performed. It was shown that some of the factors which affect the accuracy of the measurements are related to the temperature dependence of the laminar burning velocity. A method to evaluate asymmetric heat fluxes in the plate of the heat flux burner was proposed. The work reported in the present study resulted in the necessity to re-evaluate some of the previously published data. Based on the available information from literature, as well as on the results obtained in the present study, recommendations were made on how to control or reduce several experimental uncertainties associated with the heat flux method. The structure of NH3 and CH4 flames was investigated with the aim of further kinetic model development. Intracavity laser absorption spectroscopy was applied to record HCO concentration profiles in rich low-pressure CH4 mixtures and predictions of two widely used kinetic models were analyzed. Minor and major species concentrations in NH3 + air flames were used to validate four contemporary H/N/O reaction schemes and investigate the performance of the best one.
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| 9. |
- Alekseev, Vladimir, et al.
(författare)
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Laminar premixed flat non-stretched lean flames of hydrogen in air
- 2015
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Ingår i: Combustion and Flame. - : Elsevier BV. - 0010-2180. ; 162:10, s. 4063-4074
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Tidskriftsartikel (refereegranskat)abstract
- Laminar burning velocity of lean hydrogen + air flames at standard conditions is still a debated topic in combustion. The existing burning velocity measurements possess a large spread due to the use of different measurement techniques and data processing approaches. The biggest uncertainty factor in these measurements comes from the necessity to perform extrapolation to the flat flame conditions, since all of the previously obtained data were recorded in stretched flames. In the present study, laminar burning velocity of lean hydrogen + air flames and its temperature dependence were for the first time studied in stretch-free flat flames on a heat flux burner. The equivalence ratio was varied from 0.375 to 0.5 and the range of the unburned gas temperatures was 278-358 K. The flat flames tended to form cells at adiabatic conditions, therefore special attention was paid to the issue of their appearance. The shape of the flames was monitored by taking OH* images with an EM-CCD camera. In most cases, the burning velocity had to be extrapolated from flat subadiabatic conditions, and the impact of this procedure was quantified by performing measurements in H-2 + air mixtures diluted by N-2. The effect of extrapolation was estimated to be of negligible importance for the flames at standard conditions. The measured burning velocities at 298 K showed an important difference to the previously obtained literature values. The temperature dependence of the burning velocity was extracted from the measured results. It was found to be in agreement with the trends predicted by the detailed kinetic modeling, as opposed to a vast majority of the available literature data. (C) 2015 The Combustion Institute. Published by Elsevier Inc. All rights reserved.
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| 10. |
- Alekseev, Vladimir, et al.
(författare)
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The effect of temperature on the adiabatic burning velocities of diluted hydrogen flames: A kinetic study using an updated mechanism
- 2015
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Ingår i: Combustion and Flame. - : Elsevier BV. - 0010-2180. ; 162:5, s. 1884-1898
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Tidskriftsartikel (refereegranskat)abstract
- The effect of temperature on the adiabatic burning velocities of diluted hydrogen flames has been analyzed using an updated version of the Konnov detailed reaction mechanism for hydrogen. The contemporary choice of the reaction rate constants is provided with the emphasis on their uncertainties, and the analysis of the performance of the updated mechanism is presented and compared to the previous version for a wide range of validation cases: jet stirred and flow reactors; oxidation, decomposition and ignition in shock waves; ignition in rapid compression machines; laminar burning velocity and flame structure. An overall improvement of the mechanism performance was observed, particularly for the shock tube and flow reactor studies. Temperature dependence of the burning velocity, S-L, is commonly interpreted using the correlation S-L = S-L0 (T/T-0)(alpha). The updated mechanism was applied to study the behavior of the power exponent alpha for H-2 + O-2 + N-2 flames in a wide range of stoichiometry and dilution ratios. The simulations were compared to the available experimental results, either taken from the literature or evaluated in the present study from the existing burning velocity data. The equivalence ratio and N-2 content in the mixture were found to have significant influence on the temperature power exponent. The dependence of the temperature exponent on the fitting temperature range was observed and discussed. This effect was found to cause significant discrepancies in the burning velocities at high temperatures, if obtained with empirical correlation. (C) 2014 The Combustion Institute. Published by Elsevier Inc. All rights reserved.
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| 11. |
- Brackmann, Christian, et al.
(författare)
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Strategy for improved NH2 detection in combustion environments using an Alexandrite laser
- 2017
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Ingår i: Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy. - : Elsevier BV. - 1386-1425. ; 184, s. 235-242
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Tidskriftsartikel (refereegranskat)abstract
- A new scheme for NH2 detection by means of laser-induced fluorescence (LIF) with excitation around wavelength 385 nm, accessible using the second harmonic of a solid-state Alexandrite laser, is presented. Detection of NH2 was confirmed by identification of corresponding lines in fluorescence excitation spectra measured in premixed NH3-air flames and on NH2 radicals generated through NH3 photolysis in a nonreactive flow at ambient conditions. Moreover, spectral simulations allow for tentative NH2 line identification. Dispersed fluorescence emission spectra measured in flames and photolysis experiments showed lines attributed to vibrational bands of the NH2 A2A1 ← X2B1 transition but also a continuous structure, which in flame was observed to be dependent on nitrogen added to the fuel, apparently also generated by NH2. A general conclusion was that fluorescence interferences need to be carefully considered for NH2 diagnostics in this spectral region. Excitation for laser irradiances up to 0.2 GW/cm2 did not result in NH2 fluorescence saturation and allowed for efficient utilization of the available laser power without indication of laser-induced photochemistry. Compared with a previously employed excitation/detection scheme for NH2 at around 630 nm, excitation at 385.7 nm showed a factor of ~ 15 higher NH2 signal. The improved signal allowed for single-shot NH2 LIF imaging on centimeter scale in flame with signal-to-noise ratio of 3 for concentrations around 1000 ppm, suggesting a detection limit around 700 ppm. Thus, the presented approach for NH2 detection provides enhanced possibilities for characterization of fuel-nitrogen combustion chemistry.
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| 12. |
- Brackmann, Christian, et al.
(författare)
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Structure of premixed ammonia plus air flames at atmospheric pressure: Laser diagnostics and kinetic modeling
- 2016
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Ingår i: Combustion and Flame. - : Elsevier BV. - 0010-2180. ; 163, s. 370-381
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Tidskriftsartikel (refereegranskat)abstract
- The structure of premixed ammonia air flames, burning at atmospheric pressure under strain-stabilized conditions on a porous-plug burner, has been investigated using laser-diagnostic methods. Profiles of OH, NH, and NO were acquired by laser-induced fluorescence (LIF) and quantitative concentrations of OH and NO were retrieved using a concept for calibration versus absorption utilizing the LIF-signal itself, whereas NH concentrations were evaluated employing a saturated fluorescence signal. In addition, temperatures and relative oxygen concentrations were measured by rotational Coherent Anti-stokes Raman Spectroscopy (CARS). The new experimental data for flames with equivalence ratios of 0.9, 1.0, and 1.2 were used to validate and rank the performance of four contemporary detailed kinetic models. Simulations were carried out using experimental temperature profiles as well as by solving the energy equation. Two models of the same origin, developed by Mendiara and Glarborg (2009) and by Klippenstein et al. (2011), in most cases showed good agreement in terms of radical concentrations, however, the model of Mendiara and Glarborg had better prediction of temperatures and flame front positions. The model by Shmakov et al. (2010) had comparable performance concerning radical species, but significant discrepancies appeared in the prediction of flame front positions. The model of Duynslaegher et al. (2012), in addition to the flame front positions, deviated from experiments or other models in terms of NH and NO concentrations. A sensitivity analysis for the Mendiara-Glarborg mechanism indicated that remaining uncertainties of the rate constants implemented in the recent H/N/O models are difficult to scrutinize unambiguously due to experimental uncertainties. (C) 2015 The Combustion Institute. Published by Elsevier Inc. All rights reserved.
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| 13. |
- Capriolo, Gianluca, et al.
(författare)
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An experimental and kinetic study of propanal oxidation
- 2018
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Ingår i: Combustion and Flame. - : Elsevier BV. - 0010-2180. ; 197, s. 11-21
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Tidskriftsartikel (refereegranskat)abstract
- Propanal is a critical stable intermediate derived from the oxidation of 1-propanol, a promising alcohol fuel additive. To deepen the knowledge and accurately describe propanal combustion characteristics, new burning velocity measurements at different temperatures were carried out and a new detailed kinetic mechanism for propanal was proposed. Experiments were performed using the heat flux method and compared with literature data. Important discrepancies were noted between the new and available data, and possible reasons were suggested. Flow rate sensitivity analysis highlighted that, as expected, the important reactions influencing the propanal oxidation in flames are pertinent to H2 and CO sub-mechanism. Current mechanism is based on the most recent Konnov model, extended to include propanal chemistry subset. Rate constant parameters were selected based on careful evaluation of experimental and theoretical data available in literature. Model validation included assessment against a large set of combustion experiments obtained at different regimes, i.e. flames, shock tubes, and well stirred reactor, as well as comparison with the semi-detailed (lumped) kinetic mechanism for hydrocarbon and oxygenated fuels from Politecnico di Milano, detailed kinetic model from Veloo et al. and low temperature oxidation of aldehydes kinetic model of Pelucchi et al. The proposed model reproduced experimental burning velocities, ignition delay times, flame structure and JSR data with an overall good fidelity, while it reproduces only qualitatively the species distribution of propanal pyrolysis.
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| 14. |
- Fomin, Alexey, et al.
(författare)
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Experimental and modelling study of 1CH2 in premixed very rich methane flames
- 2016
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Ingår i: Combustion and Flame. - : Elsevier BV. - 0010-2180. ; 171, s. 198-210
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Tidskriftsartikel (refereegranskat)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.
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| 15. |
- Fomin, Alexey, et al.
(författare)
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Fiber Laser Intracavity Spectroscopy of hot water for temperature and concentration measurements
- 2015
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Ingår i: Applied Physics B. - : Springer Science and Business Media LLC. - 0946-2171 .- 1432-0649. ; 121:3, s. 345-351
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Tidskriftsartikel (refereegranskat)abstract
- The feasibility of temperature and concentration measurements using near-IR (similar to 1.5 mu m) water spectra obtained by fiber laser intracavity spectroscopy was evaluated. The spectra were registered with water vapor heated in a tubular oven at temperatures between 1000 and 1300 K and in adiabatic flames where temperatures were above 1800 K. Adiabatic flames of methane were stabilized on the heat flux burner. For temperature and concentration evaluation, the observed spectra were fitted by simulated spectra calculated utilizing the HITEMP database. Several discrepancies between HITEMP data and the experiments leading to significant errors in evaluation were found. After small corrections to the database better, accuracy of the temperature (+/- 70 K) and concentration (+/- 20 %) measurements is obtained. A more precise spectroscopic assignment is needed to improve the accuracy of the results.
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| 16. |
- Fomin, Alexey, et al.
(författare)
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Intracavity Laser Absorption Spectroscopy Study of HCO Radicals during Methane to Hydrogen Conversion in Very Rich Flames
- 2015
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Ingår i: Energy & Fuels. - : American Chemical Society (ACS). - 0887-0624 .- 1520-5029. ; 29:9, s. 6146-6154
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Tidskriftsartikel (refereegranskat)abstract
- Stoichiometric and very rich flames of methane have been investigated using nonintrusive laser diagnostics. Absolute concentration profiles of HCO were measured by intracavity laser absorption spectroscopy, and temperature profiles were obtained with laser-induced fluorescence of OH. Premixed CH4 + O-2 + N-2 flames were stabilized at a pressure of 30 +/- 0.3 Torr. These new experimental data were compared with predictions of two models: GRI-mech. 3.0 and Aramco mech. 1.3. GRI-mech. performs better in a stoichiometric flame, whereas Aramco mech. is in better agreement with experiments in the rich flames. Detailed analysis of the behavior of these two models revealed that similar performance is essentially fortuitous and explained by balancing of different reactions involved in HCO formation and consumption.
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| 17. |
- Sileghem, L., et al.
(författare)
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Laminar burning velocities of primary reference fuels and simple alcohols
- 2014
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Ingår i: Fuel. - : Elsevier BV. - 1873-7153 .- 0016-2361. ; 115, s. 32-40
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Tidskriftsartikel (refereegranskat)abstract
- Laminar burning velocities for methanol, ethanol, and binary and quaternary mixtures of these with isooctane and n-heptane, have been determined using the heat flux method on a flat flame adiabatic burner. Measurements were done for an equivalence ratio range between 0.7 and 1.5 and for a range of temperatures between 298 K and 358 K at atmospheric pressure. The present study expands the available data on laminar burning velocities of alcohol-hydrocarbon blends and validates simple mixing rules for predicting the laminar burning velocity for a wider range of fuel blends of hydrocarbons with methanol and/or ethanol. It is shown that simple mixing rules that consider the energy fraction of the blend's components are accurate enough to predict the experimentally determined laminar burning velocity of the mixtures. (c) 2013 Elsevier Ltd. All rights reserved.
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| 18. |
- Sileghem, L., et al.
(författare)
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Laminar burning velocity of gasoline and the gasoline surrogate components iso-octane, n-heptane and toluene
- 2013
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Ingår i: Fuel. - : Elsevier BV. - 1873-7153 .- 0016-2361. ; 112, s. 355-365
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Tidskriftsartikel (refereegranskat)abstract
- Laminar burning velocities have been measured using the heat flux method on a flat flame adiabatic burner. Measurements were done for iso-octane, n-heptane, toluene, a toluene reference fuel (i.e., a mixture of iso-octane, n-heptane and toluene) and a commercial gasoline. The laminar burning velocities of the toluene reference fuel were in correspondence with the laminar burning velocities of the commercial gasoline. Measurements were done for an equivalence ratio from 0.7 to 1.3 and for a range of temperatures between 298 K and 358 K. The temperature dependence of the fuels is shown and the measurements are compared to literature data and simulations using reduced kinetic models. (C) 2013 Elsevier Ltd. All rights reserved.
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| 19. |
- Thorsen, Lauge S., et al.
(författare)
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High pressure oxidation of NH3/n-heptane mixtures
- 2023
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Ingår i: Combustion and Flame. - 0010-2180. ; 254
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Tidskriftsartikel (refereegranskat)abstract
- Oxidation of NH3/n-heptane mixtures at pressures up to 100 atm and temperatures of 400–900 K was characterized experimentally in a laminar flow reactor and a jet-stirred reactor. A detailed chemical kinetic model was developed, updating the hydrogen and amine subsets and introducing a subset for the chemical coupling with emphasis on the NH2+n-heptane reaction. The kinetic model provided a good prediction of the ignition delay times measured in a rapid compression machine by Yu et al. (Combust. Flame 217 (2020) 2–11) as well as the high pressure experimental data obtained in the present work. The results show that it is important to include updated rate constants for NH2 + HO2 and NH2 + n-C7H16 to obtain reliable predictions for ignition and oxidation of NH3/n-heptane mixtures at high pressure. The effectiveness of implementing analogy rules for determining the rate constant of the key reaction NH2 + n-C7H16 was confirmed by the observed results.
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| 20. |
- Zamashchikov, V. V., et al.
(författare)
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Laminar burning velocities of rich near-limiting flames of hydrogen
- 2014
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Ingår i: International Journal of Hydrogen Energy. - : Elsevier BV. - 1879-3487 .- 0360-3199. ; 39:4, s. 1874-1881
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Tidskriftsartikel (refereegranskat)abstract
- In the present work, near-limiting hydrogen flames were investigated both experimentally and numerically. Very rich hydrogen + air flames were studied in a constant volume bomb equipped with a pressure sensor and a Schlieren system for optical registration of the flame front movement. The mixtures contained 70% and 75% of hydrogen, the rest being air. The measurements were conducted at pressures from 1 to 4 atm for 70% H-2 + air mixture and from 0.7 to 1.4 atm for 75% H-2 + air mixture. Two methods for determination of the laminar burning velocity were used: from the temporal evolution of the flame front movement and from the pressure records at nearly constant pressure. These methods were compared and discussed in terms of accuracy and implicit assumptions behind them. Markstein lengths were also extracted and compared with the literature by using different extrapolation models. An important role of the critical radius for extraction of the burning velocity and Markstein length is demonstrated. New experimental data are compared with three models for hydrogen combustion to elucidate the need for their further development. Copyright (C) 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.
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