| 1. |
- Oliveira, M. H. de Andrade, et al.
(författare)
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Soot, PAH and OH measurements in vaporized liquid fuel flames
- 2013
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Ingår i: Fuel. - : Elsevier BV. - 1873-7153 .- 0016-2361. ; 112, s. 145-152
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Tidskriftsartikel (refereegranskat)abstract
- Qualitative measurements of both OH and polycyclic aromatic hydrocarbons (PAH) as well as quantitative data of soot volume fraction f(v) have been obtained in vaporized liquid fuels, with the main goal of providing experimental data for combustion models and numerical mechanism validation. Measurements were carried out in a laminar coflow burner which was designed, built and integrated with an evaporation system, enabling the combustion of vaporized liquid fuels at pressures of up to 3.0 MPa to be studied. The fuels n-heptane and n-decane, referred to in the literature as being important surrogate fuels, were selected for measurements at atmospheric pressure that were carried out in the experimental setup described, making use of a combination of the Laser Induced Fluorescence (LIF) and Laser Induced Incandescence (LII) techniques. Partially premixed flames of n-heptane and n-decane showed similar combustion characteristics in the range of 1.9 < phi < 3.7. For both of the fuels the threshold for soot formation was found to be at about phi similar to 3.3. Comparison of the LIF and LII measurements for the n-heptane flames within the range of 3.7 <= phi <= 8.5 indicated the maximum PAH LIF signal to be a good predictor of f(vmax) obtained from LII. Excitation at 266 nm using delayed detection was found to result in the signals obtained showing a close linear correlation with the soot volume fraction obtained from LII when prompt detection at 1064 nm excitation was used. Neither the effects of any additional photo-chemical processes making use of high laser power at 266 nm nor the effects of particle size on the delayed gate times appeared to be of any significance for the flame conditions studied here. (C) 2013 Elsevier Ltd. All rights reserved.
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| 2. |
- van Lipzig, J. P. J., et al.
(författare)
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Laminar burning velocities of n-heptane, iso-octane, ethanol and their binary and tertiary mixtures
- 2011
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Ingår i: Fuel. - : Elsevier BV. - 1873-7153 .- 0016-2361. ; 90:8, s. 2773-2781
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Tidskriftsartikel (refereegranskat)abstract
- Measurements of the adiabatic laminar burning velocities of n-heptane, iso-octane, ethanol and their binary and tertiary mixtures are reported. 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 when the net heat loss from the flame to the burner is zero. Initial temperatures of the gas mixtures with air were 298 and 338 K. Uncertainties of the measurements were analyzed and assessed experimentally. The overall accuracy of the burning velocities was estimated to be better than +/- 1 cm/s. These new measurements were compared with the literature data when available. Experimental results in lean ethanol + air mixtures are systematically higher than previous measurements under similar conditions. Good agreement for n-heptane + air flames and for iso-octane + air flames was found with the experiments performed in counter-flow twin flames with linear extrapolation to zero stretch. (C) 2011 Elsevier Ltd. All rights reserved.
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| 3. |
- Verhoeven, L. M., et al.
(författare)
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A numerical and experimental study of Polycyclic Aromatic Hydrocarbons in a laminar diffusion flame
- 2013
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Ingår i: Proceedings of the Combustion Institute. - : Elsevier BV. - 1540-7489. ; 34, s. 1819-1826
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Tidskriftsartikel (refereegranskat)abstract
- During the process of biomass gasification tars are formed which exit the gasifier in vapor phase. Tar condensation creates problems like fouling and plugging of after-treatment, conversion and end-use equipment. Gasification tars consist mainly of Polycyclic Aromatic Hydrocarbons (PAHs). Former research has shown the possibilities and difficulties of tar conversion by partial combustion. Basic studies to investigate the oxidation of tars in non-premixed combustion processes are expected to give more insight in this problem. In this paper the ability of the flamelet-generated manifold (FGM) approach to numerically model multi-dimensional, laminar, non-premixed flames with the inclusion of PAH chemistry is investigated. Modeling detailed PAH chemistry requires the employment of large reaction mechanisms which lead to expensive numerical calculations. The application of a reduction technique like FGM leads to a considerable decrease (up to two orders) in the required computation time. A 1D numerical validation shows that the improvements achieved by implementing a varying Lewis number for the progress variable Y are significant for PAH species with a large Lewis number, such as C10H8. Considerable improvements are found near the flame front and on the fuel side of the flame. A comparison has been made of FGM results with qualitative Planar Laser Induced Fluorescence (PLIF) measurements. A laminar CH4/N-2-air co-flow flame has been doped with two dopants, benzene and toluene, at three different concentrations. A set of filters was used in order to qualitatively distinguish the small (1-2 rings) and large (3 or more rings) aromatic species. The results show that the model is able to capture the major flame characteristics typical for PAH formation in multi-dimensional laminar non-premixed flames. (C) 2012 The Combustion Institute. Published by Elsevier Inc. All rights reserved.
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| 4. |
- Goswami, M., et al.
(författare)
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Laminar burning velocity of lean H-2-CO mixtures at elevated pressure using the heat flux method
- 2014
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Ingår i: International Journal of Hydrogen Energy. - : Elsevier BV. - 1879-3487 .- 0360-3199. ; 39:3, s. 1485-1498
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Tidskriftsartikel (refereegranskat)abstract
- Laminar burning velocity measurements of 50:50 and 85:15% (by volume) H-2-CO mixtures with O-2-N-2 and O-2-He oxidizers were performed at lean conditions (equivalence ratio from 0.5 to 1) and elevated pressures (1 atm-9 atm). The heat flux method (HFM) is employed for determining the laminar burning velocity of the fuel-oxidizer mixtures. HFM creates a one-dimensional adiabatic stretchless flame which is an important prerequisite in defining the laminar burning velocity. This technique is based on balancing the heat loss from the flame to the burner with heat gain to the unburnt gas mixture, in a very simple way, such that no net heat loss to the burner is obtained. Instabilities are observed in lean H-2-CO flames with nitrogen as the bath gas for pressures above 4 atm. Stable flames are obtained with helium as the bath gas for the entire pressure range. With the aim to cater stringent conditions for combustion systems such as gas turbines, an updated H-2-CO kinetic mechanism is proposed and validated against experimental results. The scheme was updated with recent rate constants proposed in literature to suit both atmospheric and elevated pressures. The proposed kinetic model agrees with new experimental results. At conditions of high pressure and lean combustion, reactions H + O-2 = OH + O and H + O-2 (+M) = H-2 (+M) compete the most when compared to other reactions. Reaction H + HO2 = OH + OH contributes to OH production, however, less at high-pressure conditions. At higher CO concentrations and leaner mixtures an important role of reaction CO + OH = CO2 + H is observed in the oxidation of CO. Copyright (C) 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.
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| 5. |
- Goswami, M., et al.
(författare)
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Numerical Simulations of Flat Laminar Premixed Methane-Air Flames at Elevated Pressure
- 2014
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Ingår i: Combustion Science and Technology. - : Informa UK Limited. - 1563-521X .- 0010-2202. ; 186:10-11, s. 1447-1459
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Tidskriftsartikel (refereegranskat)abstract
- Two-dimensional axisymmetric simulation of stoichiometric methane-air flames stabilized on flat burners at elevated pressure is reported in the present work. Such flames, in practice, are experimentally obtained using the heat flux method for measurement of laminar burning velocity of fuel-oxidizer mixtures (Bosschaart and de Goey, 2004; Goswami et al., 2013). The method makes use of a burner with a perforated brass burner plate. The dimensions of such a plate play an important role in creating flat flames. The present investigation is focused on studying laminar premixed flame structure numerically at elevated pressure up to 15 bar using a one-step and a detailed chemical reaction mechanism. Three burner plate models (of varying hole diameter and porosity) are used in the simulations for pressures up to 7 bar with a one-step mechanism. The surface area increase of the flame was evaluated based on an isotherm at 900 K and the net reaction rate of methane compared to a flat flame. The comparison of these models shows that the surface area increase can significantly be reduced by choosing a smaller hole diameter and larger porosity. The results of the detailed simulations using an appropriate chemical reaction mechanism up to 15 bar using a burner plate model, which is similar to the ones used in experiments (mentioned above), show a nonlinear increase of the flame curvature with elevating pressure. A hole diameter of 0.25 mm and a pitch of 0.29 mm is suggested for a burner plate in such experiments. Flame structure at elevated pressure is also analyzed further based on species profiles obtained.
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| 6. |
- Heimdal Nilsson, Elna, et al.
(författare)
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Laminar burning velocities of acetone in air at room and elevated temperatures
- 2013
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Ingår i: Fuel. - : Elsevier BV. - 1873-7153 .- 0016-2361. ; 105, s. 496-502
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Tidskriftsartikel (refereegranskat)abstract
- Laminar burning velocities of acetone + air mixtures at initial gas mixture temperatures of 298, 318, 338 and 358 K are reported. Non-stretched flames were stabilized on a perforated plate burner at 1 atm, and laminar burning velocities were determined using the heat flux method, at conditions where the net heat loss from the flame to the burner is zero. The overall accuracy of the burning velocities was estimated to be better than +/- 1.0 cm s (1). Very good reproducibility of the results and excellent agreement with modeling using a recently updated chemical kinetic model brings confidence in the validity of the reported results. Previous determinations of laminar burning velocities for acetone have provided inconsistent results. In the present work it is suggested that this can in part be attributed to the chemically aggressive nature of acetone. (C) 2012 Elsevier Ltd. All rights reserved.
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| 7. |
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| 8. |
- Hosseini, N., et al.
(författare)
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Development of a numerical model for obtaining flame transfer function in a simplified slit burner with heat exchanger
- 2014
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Ingår i: 21st International Congress on Sound and Vibration 2014, ICSV 2014. ; , s. 1581-1588
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Konferensbidrag (refereegranskat)abstract
- The goal of the present work is to develop a model to investigate the interactions between a burner and a heat exchanger, looking from a hydrodynamic and thermo-acoustic point of view. Thermo-acoustics of laminar premixed flames in open air have been studied by several researchers in the past decades. However, a burner in open air may behave differently compared to if situated in a combustion chamber enclosure. This could be related to the effect of temperature, the effect of flame shape (e.g. flames impinging on the heat exchanger walls in compact boilers), distribution of the flame on the burner deck, etc. The behavior of a linear array of a multiple Bunsen-type flames is studied on a 2D geometry in a CFD code to simulate the effects of heat exchanger addition on the thermo-acoustics of the flames. The location of the heat exchanger surface is varied for different conditions of power. A step profile velocity perturbation is used for obtaining the response of the flame represented within the flame transfer function approach. The calculated gain and phase of the flame transfer function are compared for different cases as the indicator of the thermo-acoustic behavior. Results show that the main parameter having considerable influence is the burner load and flame shape. The setup to experimentally investigate these effects will be constructed in near future.
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| 9. |
- Konnov, Alexander, et al.
(författare)
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2D effects in laminar premixed flames stabilized on a flat flame burner
- 2013
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Ingår i: Experimental Thermal and Fluid Science. - : Elsevier BV. - 1879-2286 .- 0894-1777. ; 47, s. 213-223
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Tidskriftsartikel (refereegranskat)abstract
- In the present work non-idealities of flat burner-stabilized flames at atmospheric and low pressures are examined using PIV measurements, which are supported by and analyzed with the help of CFD modeling. Radial and axial velocity profiles measured in the cold flow and in the flames at atmospheric and at lower pressures are presented. Two possible reasons for the drop in the apparent laminar burning velocity at low pressures (below 20 kPa) were considered: the non-uniformity of the velocity profile issuing from the burner mouth and diffusion of the gas mixture from the original gas flow. At very low pressures an outward velocity at the edge of the burner plate is detected. A part of the fuel-air mixture therefore seems to escape the flow at the edge of the burner. Further experiments, however, revealed that diffusion of the fuel from the fresh mixture and of the ambient atmosphere into the flame is less important as compared to the diffusive loss of H atoms from the flame at low pressures. This was substantiated by the numerical analysis and assessment of the earlier observations from the literature. A critical relation between the size of the burner and the lowest pressure for ensuring the stabilization of a flat flame is demonstrated. (C) 2013 Elsevier Inc. All rights reserved.
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| 10. |
- Konnov, Alexander, et al.
(författare)
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Adiabatic laminar burning velocities of CH4 + H2 + air flames at low pressures
- 2010
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Ingår i: Fuel. - : Elsevier BV. - 1873-7153 .- 0016-2361. ; 89:7, s. 1392-1396
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Tidskriftsartikel (refereegranskat)abstract
- Experimental measurements of the adiabatic burning velocity in methane + hydrogen + air flames using the Heat Flux method are presented. The hydrogen content in the fuel was varied from 0 to 20%. Non-stretched flames were stabilized on a perforated plate burner from 20 to 100 kPa. The equivalence ratio was varied from 0.8 to 1.4. Adiabatic burning velocities of CH4 + H-2 + air mixtures were found in good agreement with the literature results at atmospheric pressure. Also low-pressure measurements in CH4 + air flames performed earlier were accurately reproduced. The effects of enrichment by hydrogen on the laminar burning velocity at low pressures have been studied for the first time. Calculated burning velocities using the Konnov mechanism are in satisfactory agreement with the experiments over the entire range of conditions. Pressure dependences of the burning velocities for the three fuels studied could be approximated by an empirical exponential correlation. (C) 2009 Elsevier Ltd. All rights reserved.
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| 11. |
- Konnov, Alexander, et al.
(författare)
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The temperature dependence of the laminar burning velocity of ethanol flames
- 2011
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Ingår i: Proceedings of the Combustion Institute. - : Elsevier BV. - 1540-7489. ; 33, s. 1011-1019
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Tidskriftsartikel (refereegranskat)abstract
- The Heat Flux method was extended for the first time towards liquid fuels and used to determine burning velocities under conditions when the net heat loss from the flame to the burner is zero. Non-stretched flames were stabilized on a perforated plate burner at 1 atm. Uncertainties of the measurements were analyzed and assessed experimentally. The overall accuracy of the burning velocities was estimated to be better than +/- 1 cm/s. Excellent reproducibility of the experiments over an extended period of time was demonstrated. Measurements of the adiabatic burning velocity of ethanol + air flames in the range of initial mixture temperatures from 298 to 358 K are presented. Experimental results are in a good agreement with the recent literature data obtained in constant volume bombs. Both the ethanol combustion mechanism of Saxena and Williams and the Konnov mechanism significantly over-predict ethanol laminar burning velocities in lean and near-stoichiometric mixtures. The effects of initial temperature on the adiabatic laminar burning velocities of ethanol 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 at atmospheric pressure. Experimental data and proposed empirical expressions for alpha as a function of equivalence ratio were summarized. They were compared with the predictions of detailed kinetic models. The existence of a minimum in alpha in the slightly rich mixtures is demonstrated experimentally and confirmed computationally. (C) 2010 The Combustion Institute. Published by Elsevier Inc. All rights reserved.
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| 12. |
- Li, Bo, et al.
(författare)
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Accurate measurements of laminar burning velocity using the Heat Flux method and thermographic phosphor technique
- 2011
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Ingår i: Proceedings of the Combustion Institute. - : Elsevier BV. - 1540-7489. ; 33, s. 939-946
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Tidskriftsartikel (refereegranskat)abstract
- The Heat Flux method was further developed to significantly reduce its experimental uncertainty and used to determine burning velocities under conditions when the net heat loss from the flame to the burner is zero. Non-stretched flames were stabilized on a perforated plate burner at 1 atm. Measurements of the adiabatic burning velocity of methane air flames at initial mixture temperatures of 318 K are presented. Previously, tiny thermocouples in the thin burner plate were used to evaluate when the heat flux of the flame to the burner is zero. Related errors limit the accuracy of the method so far. A new experimental procedure based on thermographic phosphors is described which avoids these errors. The new experimental procedure is described. An UV thermographic phosphor ZnO:Zn was selected and used to sensitively control the temperature uniformity on the burner plate to within 60 mK. Uncertainties of the measurements were analyzed and assessed experimentally. A more accurate evaluation of the gas velocities, using mass weighting, was introduced to increase the accuracy further. The uncertainty of the measured adiabatic burning velocities due to the temperature scattering can be reduced from typically +/-1.5 cm s at Phi = 0.7 methane air flame to +/-0.25 cm s. The overall accuracy of the burning velocities including the uncertainty from the employed mass flow controllers was evaluated to be better than +/-0.35 cm s. Possibilities to further improve the measurement accuracy are discussed with practical considerations. (C) 2010 The Combustion Institute. Published by Elsevier Inc. All rights reserved.
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| 13. |
- Prins, M. J., et al.
(författare)
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Biomass pyrolysis in a heated-grid reactor: Visualization of carbon monoxide and formaldehyde using Laser-Induced Fluorescence
- 2011
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Ingår i: Journal of Analytical and Applied Pyrolysis. - : Elsevier BV. - 1873-250X .- 0165-2370. ; 92:2, s. 280-286
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Tidskriftsartikel (refereegranskat)abstract
- The development of improved biomass pyrolysis models is vital for more accurate modelling and design of biomass conversion equipment. Such improved models must be based on reliable experimental data: biomass should be pyrolyzed at high heating rates and the reaction products should be measured using an on-line, non-intrusive method. Therefore, a heated grid reactor with heating rate of 300-600 K/s was used to study pyrolysis of biomass at temperatures in the range of 500-700 degrees C. The formation of formaldehyde and carbon monoxide from wood at high heating rates was successfully visualized using Laser-Induced Fluorescence (LIF). A thin vertical laser line or sheet was present directly above the biomass lying on the heated grid. Two-photon excitation at 230 nm was applied to induce fluorescence of carbon monoxide present in the volatiles, whereas excitation of formaldehyde was done at 355 nm. Visualization of these compounds shows that the release rises strongly with temperature; this typically happens on a timescale in the order of seconds. In principle, the method described allows for the determination of truly primary products. Future research is recommended, aimed at quantifying the concentrations measured by LIE. Care must be taken to calibrate for quenching of the fluorescence signal. Avoiding secondary reactions taking place in the gas phase is another experimental challenge. (C) 2011 Elsevier B.V. All rights reserved.
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| 14. |
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| 15. |
- Yu, M., et al.
(författare)
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Survivability of thermographic phosphors (YAG:Dy) in a combustion environment
- 2010
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Ingår i: Measurement Science & Technology. - : IOP Publishing. - 0957-0233 .- 1361-6501. ; 21:3
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Tidskriftsartikel (refereegranskat)abstract
- The feasibility of applying laser-induced phosphorescence in a combustion environment was shown by testing the consistency of the emission-temperature relations of thermographic phosphor particles (YAG:Dy). The relations were calibrated before and after the phosphor particles had passed a flame front. The calibrations were performed in air and in pure oxygen. The emission-temperature relation prevails from around 300 K to 1300 K. The difference in emission-temperature relation for the two different cases is less than the experimental precision (3%).
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