| 1. |
- Oliveira, M. H. de Andrade, et al.
(författare)
-
Soot, PAH and OH measurements in vaporized liquid fuel flames
- 2013
-
Ingår i: Fuel. - : Elsevier BV. - 1873-7153 .- 0016-2361. ; 112, s. 145-152
-
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.
|
|
| 2. |
- van Lipzig, J. P. J., et al.
(författare)
-
Laminar burning velocities of n-heptane, iso-octane, ethanol and their binary and tertiary mixtures
- 2011
-
Ingår i: Fuel. - : Elsevier BV. - 1873-7153 .- 0016-2361. ; 90:8, s. 2773-2781
-
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.
|
|
| 3. |
- Verhoeven, L. M., et al.
(författare)
-
A numerical and experimental study of Polycyclic Aromatic Hydrocarbons in a laminar diffusion flame
- 2013
-
Ingår i: Proceedings of the Combustion Institute. - : Elsevier BV. - 1540-7489. ; 34, s. 1819-1826
-
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.
|
|
| 4. |
- Akkerman, V., et al.
(författare)
-
Flow-flame interaction in a closed chamber
- 2008
-
Ingår i: Physics of Fluids. - : AIP Publishing. - 1070-6631 .- 1089-7666. ; 20:5, s. 21-
-
Tidskriftsartikel (refereegranskat)abstract
- Numerous studies of flame interaction with a single vortex and recent simulations of burning in vortex arrays in open tubes demonstrated the same tendency for the turbulent burning rate proportional to U-rms lambda(2/3), where U-rms is the root-mean-square velocity and lambda is the vortex size. Here, it is demonstrated that this tendency is not universal for turbulent burning. Flame interaction with vortex arrays is investigated for the geometry of a closed burning chamber by using direct numerical simulations of the complete set of gas-dynamic combustion equations. Various initial conditions in the chamber are considered, including gas at rest and several systems of vortices of different intensities and sizes. It is found that the burning rate in a closed chamber (inverse burning time) depends strongly on the vortex intensity; at sufficiently high intensities it increases with U-rms approximately linearly in agreement with the above tendency. On the contrary, dependence of the burning rate on the vortex size is nonmonotonic and qualitatively different from the law lambda(2/3). It is shown that there is an optimal vortex size in a closed chamber, which provides the fastest total burning rate. In the present work, the optimal size is six times smaller than the chamber height.
|
|
| 5. |
- Goswami, M., et al.
(författare)
-
Experimental and modeling study of the effect of elevated pressure on lean high-hydrogen syngas flames
- 2015
-
Ingår i: Proceedings of the Combustion Institute. - : Elsevier BV. - 1540-7489. ; 35, s. 655-662
-
Tidskriftsartikel (refereegranskat)abstract
- New laminar burning velocity measurements of 85: 15% (by volume) H-2-CO and H-2-N-2 mixtures with O-2-He oxidizer are reported at lean conditions and elevated pressures (1-10 atm). Experiments are conducted using the heat flux method at initial temperature of 298 K. In this technique a near adiabatic flame is stabilized by balancing the heat loss from the flame to the burner with heat gain to the unburnt gas mixture such that no net heat loss to the burner is observed. A new facility was designed for such high pressure burner stabilized flame experiments. The results obtained are compared with five chemical kinetic schemes from literature for syngas mixtures at elevated pressures. Large differences are observed between the kinetic schemes and the experiments which can be attributed to certain key chemical reactions. A study of the kinetics is performed through reaction rate and sensitivity analysis which indicate that a high uncertainty still remains in important reactions that drive the production and consumption of species such as H, HO2 and OH. For lean mixtures the reaction H + O-2(+M) = HO2(+M) contributes significantly to the deviation of models from the experiments. The present analysis in the lean mixture regime suggests the need for further studies in assessment and modification of rate constants for this reaction. (C) 2014 The Combustion Institute. Published by Elsevier Inc. All rights reserved.
|
|
| 6. |
- Goswami, M., et al.
(författare)
-
Experimental and modelling study of the effect of elevated pressure on ethane and propane flames
- 2016
-
Ingår i: Fuel. - : Elsevier BV. - 1873-7153 .- 0016-2361. ; 166, s. 410-418
-
Tidskriftsartikel (refereegranskat)abstract
- Laminar burning velocities, S-L, of ethane + air and propane + air flames within an equivalence ratio range between 0.8 and 1.3 were determined at atmospheric and elevated pressures up to 4 atm. Measurements were performed in non-stretched flames, stabilized on a perforated plate burner at adiabatic conditions, created using the heat flux method. Initial unburnt gas temperature was 298 K. These new experimental results were compared with available literature data and predictions using three kinetic schemes: USC Mech II, San Diego mechanism and Aramco Mech 1.3. The models behave differently in reproducing S-L of ethane and propane flames with closer agreement between Aramco Mech 1.3 and the present measurements. The pressure dependence of the laminar burning velocities was analysed using the expression S-L = S-L0(P/P-0)(beta). Large deviations of the derived power exponent, beta, were observed for different experimental datasets and between model predictions and the measurements. To elucidate these differences in the performance of the three mechanisms, sensitivity analyses of the burning velocity and of the power exponent beta were performed. It was demonstrated that the power exponent beta may serve as an independent target for model validation and improvement. When comparing beta coefficients derived from the present and previous measurements of S-L in methane, ethane, propane and n-pentane flames using the heat flux method, important similarities were found at lean conditions with large disparity in rich mixtures. Neither experiments nor modelling support the linear dependence of the power exponent beta with equivalence ratio for flames of alkanes. (C) 2015 Elsevier Ltd. All rights reserved.
|
|
| 7. |
- Goswami, M., et al.
(författare)
-
Laminar burning velocity of lean H-2-CO mixtures at elevated pressure using the heat flux method
- 2014
-
Ingår i: International Journal of Hydrogen Energy. - : Elsevier BV. - 1879-3487 .- 0360-3199. ; 39:3, s. 1485-1498
-
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.
|
|
| 8. |
- Goswami, M., et al.
(författare)
-
Numerical Simulations of Flat Laminar Premixed Methane-Air Flames at Elevated Pressure
- 2014
-
Ingår i: Combustion Science and Technology. - : Informa UK Limited. - 1563-521X .- 0010-2202. ; 186:10-11, s. 1447-1459
-
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.
|
|
| 9. |
- Heimdal Nilsson, Elna, et al.
(författare)
-
Laminar burning velocities of acetone in air at room and elevated temperatures
- 2013
-
Ingår i: Fuel. - : Elsevier BV. - 1873-7153 .- 0016-2361. ; 105, s. 496-502
-
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.
|
|
| 10. |
|
|
| 11. |
- Hosseini, N., et al.
(författare)
-
Development of a numerical model for obtaining flame transfer function in a simplified slit burner with heat exchanger
- 2014
-
Ingår i: 21st International Congress on Sound and Vibration 2014, ICSV 2014. ; , s. 1581-1588
-
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.
|
|
| 12. |
- Hosseini, N., et al.
(författare)
-
Evaluating thermoacoustic properties of heating appliances considering the burner and heat exchanger as acoustically active elements
- 2018
-
Ingår i: Combustion and Flame. - : Elsevier. - 0010-2180 .- 1556-2921. ; 191, s. 486-495
-
Tidskriftsartikel (refereegranskat)abstract
- Heat exchangers are an essential constituent part of many combustion systems. The thermoacoustic instability in such systems is a common problem and it has been studied extensively. However, the heat exchanger has not gained much attention in the field of combustion thermoacoustics, leading to a lack of knowledge about the thermoacoustic interactions between the burner and the heat exchanger. In this paper, a modeling approach is introduced to study these interactions in an academic representation of a heating appliance, comprised of a perforated slit burner and a tube heat exchanger. Both elements are considered thermally and acoustically active. A CFD model is used in a two-dimensional domain to simulate the response of the system to small amplitude broadband velocity perturbations. The thermochemical and acoustic coupling between the burner and the heat exchanger is investigated and a method is introduced to decouple their effects and study them separately. The extents to which this method is valid are addressed by varying the distance between the elements. Results show that as long as the flames do not impinge on the heat exchanger surface, a linear network modeling approach can be applied to construct the acoustic response of the composed configuration from the responses of its constituting elements. This approach requires registering the average velocity on a properly chosen intermediate plane between the burner and heat exchanger. Choosing this plane may be to some point difficult, i.e. when the burner and heat exchanger are close and cannot be considered independent. Moreover, when flame impingement occurs, the interactions between the flame and heat exchanger affect their individual thermoacoustic behaviors and the burner plus heat exchanger assembly needs to be considered as one coupled acoustic element. Particularly, flame impingement changes the phase of the heat absorption response of the heat exchanger and it may significantly alter the acoustic properties of the coupled assembly. The physics lying behind the effects of such interactions on the thermoacoustics of the system is discussed. The obtained results signify that a correct stability prediction of an appliance with burner and heat exchangers requires considering active thermoacoustic behavior of both elements as well as their interactions.
|
|
| 13. |
- Hosseini, N., et al.
(författare)
-
Intrinsic thermoacoustic modes and their interplay with acoustic modes in a Rijke burner
- 2018
-
Ingår i: International Journal of Spray and Combustion Dynamics. - : Sage Publications. - 1756-8277 .- 1756-8285. ; 10:4, s. 315-325
-
Tidskriftsartikel (refereegranskat)abstract
- The interplays between acoustic and intrinsic modes in a model of a Rijke burner are revealed and their influence on the prediction of thermoacoustic instabilities is demonstrated. To this end, the system is examined for a range of time delays, temperature ratios and reflection coefficients as adjustable parameters. A linear acoustic network model is used and all modes with frequency below the cut-on frequency for non-planar acoustic waves are considered. The results show that when reflection coefficients are reduced, the presence of a pure ITA mode limits the reduction in the growth rate that usually results from a reduction of the reflection coefficients. In certain conditions, the growth rates can even increase by decreasing reflections. As the time delay of the flame and thus the ITA frequency decreases, the acoustic modes couple to and subsequently decouple from the pure ITA modes. These effects cause the maximum growth rate to alternate between the modes. This investigation draws a broad picture of acoustic and intrinsic modes, which is crucial to accurate prediction and interpretation of thermoacoustic instabilities.
|
|
| 14. |
- Hosseini, N., et al.
(författare)
-
Transfer function calculations of segregated elements in a simplified slit burner with heat exchanger
- 2015
-
Ingår i: 22nd International Congress on Sound and Vibration, ICSV 2015. - : International Institute of Acoustics and Vibrations. - 9788888942483
-
Konferensbidrag (refereegranskat)abstract
- A simplified burner-heat exchanger system is numerically modelled in order to investigate the effects of different elements on the response of the whole system to velocity excitation. We model the system in a 2D CFD code, considering a linear array of multiple Bunsen-type flames with heat exchanger tubes downstream the flames. Thermoacoustic instability is one of the main issues in lean premixed combustion systems, especially domestic boilers. In compact condensing boilers the close distance between the burner surface and the heat exchanger has increased the importance of studying the interactions between the flames and the heat exchanger. The elements corresponding to the heat balance in the system are the flame as heat source and burner deck and heat exchanger as heat sinks. We use both transfer function and transfer matrix approaches to identify the response of these elements to a step function excitation of velocity at the inlet of the domain. Steady-state simulations show that the contribution of the burner deck to the heat balance of the whole system is negligible, leaving the flame and heat exchanger as main contributors to the response of the system. We separately investigate the behavior of these two elements by modeling cases with flame only and heat exchanger only. Then we calculate the behavior of the combined system and compare it to the results of modeling a case with flame and heat exchanger together. These results show that, assuming linear behavior of the elements, it is possible to predict the system behavior via its constructing elements. Further investigations of the effects of other parameters and the limits, within which the assumptions are valid, are currently in progress.
|
|
| 15. |
- Kojourimanesh, M., et al.
(författare)
-
Mobius transformation between reflection coefficients at upstream and downstream sides of flame in thermoacoustics systems
- 2021
-
Ingår i: "Advances in Acoustics, Noise and Vibration - 2021" Proceedings of the 27th International Congress on Sound and Vibration, ICSV 2021. - : Silesian University Press.
-
Konferensbidrag (refereegranskat)abstract
- An alternative approach to assess the conditions for the onset of thermoacoustics combustion instability is proposed. The method is based on the analysis of the relation between the reflection coefficient of combustor upstream section (subsystems) with respect to the burner/flame, Rup, and the input reflection coefficient, Rin, as observed from the inlet of the burner with flame and all downstream subsystems of a combustion appliance. The instability of the combustor can be determined by evaluating the system dispersion relation expressed in the terms of these two reflection coefficients. The properties of the relation between Rin, the reflection coefficient of the burner downstream subsystems, Rdn, and elements of the flame transfer matrix, TM, of the burner are investigated. This relation has the form of the well-known Mobius transformation. Using the well-developed theory of the transformation, we derive the necessary conditions of Rdn to ensure that the magnitude of Rin becomes less than 1 in a frequency range. This condition results in a passive thermoacoustics stability of the system's operation. Furthermore, an optimum value of Rdn is derived which provides a minimum value of Rin at given entries of the burner TM. The practical application of the developed theory provides suitable criteria and guidelines for designing passive acoustic properties at the downstream side of the combustion appliance.
|
|
| 16. |
- Kojourimanesh, M., et al.
(författare)
-
Thermo-acoustic flame instability criteria based on upstream reflection coefficients
- 2021
-
Ingår i: Combustion and Flame. - : Elsevier BV. - 0010-2180 .- 1556-2921. ; 225, s. 435-443
-
Tidskriftsartikel (refereegranskat)abstract
- A prospective method to assess thermo-acoustic instabilities based on two reflection coefficients measured from the upstream side of the burner is presented and experimentally validated. In order to compose a model which allows predicting the onset of thermo-acoustic instability of combustion in a practical appliance, one has to characterize the thermo-acoustic properties of the burner including the flame as an acoustically active element and acoustic properties of all other (usually passive) components of the combustion appliance both upstream as well as downstream of the burner. This kind of modeling strategy usually faces serious practical problems related to the need of measurements/modeling at the hot downstream part of the system. In the present work, we propose a measurement and a system modeling approach which relies on two acoustic measurements, namely reflection coefficients, only at the cold (burner upstream) part of the combustion appliance. Both reflection coefficients, termed upstream and input, can be readily measured using standard acoustic techniques. The need to measure the input reflection coefficient of an acoustically active subsystem may impose difficulties related to the acoustic instability of the measurement setup itself. The approach and technical solution to handle this problem via a special modification of the excitation source (loudspeaker box) is proposed. The dispersion relation to search for system eigen frequencies is represented in a form that couples the reflection coefficients of the upstream part of the appliance and input reflection coefficient from the downstream part as observed through the burner with flame. This form of the dispersion relation is commonly used in the theory of radio-frequency circuits and recently introduced for thermo-acoustic problems. The proposed method is applied to burners with premixed burner-stabilized Bunsen-type flames. The observed instability conditions and oscillation frequencies are compared with predictions of the proposed modeling approach and reveal good correspondence.
|
|
| 17. |
- Konnov, Alexander, et al.
(författare)
-
2D effects in laminar premixed flames stabilized on a flat flame burner
- 2013
-
Ingår i: Experimental Thermal and Fluid Science. - : Elsevier BV. - 1879-2286 .- 0894-1777. ; 47, s. 213-223
-
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.
|
|
| 18. |
- Konnov, Alexander, et al.
(författare)
-
Adiabatic laminar burning velocities of CH4 + H2 + air flames at low pressures
- 2010
-
Ingår i: Fuel. - : Elsevier BV. - 1873-7153 .- 0016-2361. ; 89:7, s. 1392-1396
-
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.
|
|
| 19. |
- Konnov, Alexander, et al.
(författare)
-
The temperature dependence of the laminar burning velocity of ethanol flames
- 2011
-
Ingår i: Proceedings of the Combustion Institute. - : Elsevier BV. - 1540-7489. ; 33, s. 1011-1019
-
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.
|
|
| 20. |
- Li, Bo, et al.
(författare)
-
Accurate measurements of laminar burning velocity using the Heat Flux method and thermographic phosphor technique
- 2011
-
Ingår i: Proceedings of the Combustion Institute. - : Elsevier BV. - 1540-7489. ; 33, s. 939-946
-
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.
|
|
| 21. |
- Prins, A. J., et al.
(författare)
-
Visualization of Biomass Pyrolysis and Temperature Imaging in a Heated-Grid Reactor
- 2009
-
Ingår i: Energy & Fuels. - : American Chemical Society (ACS). - 0887-0624 .- 1520-5029. ; 23:1, s. 993-1006
-
Tidskriftsartikel (refereegranskat)abstract
- The main advantage of a heated-grid reactor for studying pyrolysis kinetics of solid fuel samples is that high heating rates of up to 1000 K/s can be obtained. However, one of the concerns is whether the temperature distribution over the grid material is uniform and whether the presence of a thermocouple welded to the grid causes any measurement errors. Biomass samples were placed on the heated-grid reactor, and the volatiles, emitted in the biomass pyrolysis process as hot gas plumes, were imaged with an infrared camera with a high framing speed. The temporal resolved infrared images indicate that the pyrolysis process does not take place at the same rate everywhere on the grid. Two-dimensional temperature images of a heated grid made of stainless steel were recorded using the method of laser-induced thermometry with thermographic phosphors. As expected from a heat-transfer model, measured temperatures were found to be significantly higher than temperatures indicated by a thermocouple welded to the bottom of the grid. It was also observed that there is a large temperature gradient between the two electrodes on which the grid is connected. It is shown that replacing a wire mesh by a foil as a grid material may lead to more homogeneous temperature distribution. The paper recommends additional research to demonstrate the suitability of the heated-grid reactor for carrying out accurate measurements.
|
|
| 22. |
- Prins, M. J., et al.
(författare)
-
Biomass pyrolysis in a heated-grid reactor: Visualization of carbon monoxide and formaldehyde using Laser-Induced Fluorescence
- 2011
-
Ingår i: Journal of Analytical and Applied Pyrolysis. - : Elsevier BV. - 1873-250X .- 0165-2370. ; 92:2, s. 280-286
-
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.
|
|
| 23. |
- Raida, M. B., et al.
(författare)
-
Laminar burning velocity measurements of ethanol+air and methanol+air flames at atmospheric and elevated pressures using a new Heat Flux setup
- 2021
-
Ingår i: Combustion and Flame. - : Elsevier BV. - 0010-2180. ; 230
-
Tidskriftsartikel (refereegranskat)abstract
- A new setup for burning velocity measurements of liquid fuels at elevated pressures using the Heat Flux method has been constructed. The burner design has been improved comparing to previous studies in this and other laboratories. Laminar burning velocities were determined experimentally for ethanol+air and methanol+air mixtures over a range of conditions including equivalence ratio (0.8 to 1.3), inlet gas temperature (318–338 K), and pressure (1–5 bar). Experimental uncertainties have been determined and analyzed. The overall accuracy of the burning velocity, SL, was evaluated to be better than ±1 cm/s for atmospheric pressure and ±1.5 cm/s at elevated pressure conditions. Experimental results at 1 atm are in good agreement with recent literature data. To compare the present measurements with the literature data often obtained at other initial temperatures and pressures, an empirical expression SL = SL0 (T/T0)α (p/p0)β, which correlates the burning velocity at a specific temperature, T, and pressure, p, with that at standard conditions indicated by superscripts 0, was implemented. At a fixed temperature, pressure dependence at each equivalence ratio can be analyzed. It was found that power exponents β derived in the present work and from the literature data possess large scattering. The best agreement was found between the present results and experimental literature data from spherical flames using non-linear stretch correction models. Burning velocities at atmospheric as well as elevated pressures and power exponents β have been also compared with kinetic modeling results using several detailed kinetic mechanisms, showing a fair to a good agreement. As the new results are accurate and free from stretch effects, they form a new source of reliable data for validation of the reaction mechanisms.
|
|
| 24. |
- Remie, Martin, et al.
(författare)
-
Extended heat-transfer relation for an impinging laminar flame jet to a flat plate
- 2008
-
Ingår i: International Journal of Heat and Mass Transfer. - : Elsevier BV. - 0017-9310. ; 51:7-8, s. 1854-1865
-
Tidskriftsartikel (refereegranskat)abstract
- Many industrial applications use flame impingement to obtain high heat-transfer rates. An analytical expression for the convective part of the heat transfer of a flame jet to a plate is derived. Therefore, the flame jet is approximated by a hot inert jet. In contradiction with existing convective heat-transfer relations, our analytical solution is applicable not only for large distances between the jet and the plate, but also for close spacings. Multiplying the convective heat transfer by a factor which takes chemical recombination in the cold boundary layer into account, results in an expression for the heat flux from a flame jet to the hot spot of a heated plate. Numerical and experimental validation show good agreement.
|
|
| 25. |
- Remie, Martin, et al.
(författare)
-
Heat-transfer distribution for an impinging laminar flame jet to a flat plate
- 2008
-
Ingår i: International Journal of Heat and Mass Transfer. - : Elsevier BV. - 0017-9310. ; 51:11-12, s. 3144-3152
-
Tidskriftsartikel (refereegranskat)abstract
- Impinging flame jets are widely used in applications where high heat-transfer rates are needed, for instance in the glass industry. During the heating process of glass products, internal thermal stresses develop in the material due to temperature gradients. In order to avoid excessive thermal gradients as well as overheating of the hot spots, it is important to know and control the temperature distribution inside a heated glass product. Therefore, it is advantageous to know the relation describing the convective heat–flux distribution at the heated side of a glass product. In a previous work, we presented a heat–flux relation applicable for the hot spot of the target [M.J. Remie, G. Sa¨rner, M.F.G. Cremers, A. Omrane, K.R.A.M. Schreel, M. Alde´n, L.P.H. de Goey, Extended heat-transfer relation for an impinging laminar flame jet to a flat plate, Int. J. Heat Mass Transfer, in press]. In this paper, we present an extension of this relation, which is applicable for larger radial distances from the hot spot.
|
|
| 26. |
- Saxena, V., et al.
(författare)
-
Designing an acoustic termination with a variable reflection coefficient to investigate the probability of instability of thermo-acoustic systems
- 2021
-
Ingår i: "Advances in Acoustics, Noise and Vibration - 2021" Proceedings of the 27th International Congress on Sound and Vibration, ICSV 2021. - : Silesian University Press.
-
Konferensbidrag (refereegranskat)abstract
- This paper presents results of the development of an acoustic device to be utilized as a duct termination with variable reflection coefficient. This study is motivated by the idea to experimentally evaluate the probability of instability of a thermo-acoustic system where combustion acts as an active acoustic element, and this termination acts as a passive acoustic element that can be configured to a desired value of the reflection coefficient at the upstream side of the flame and burner for lab-scaled physical modelling of, for instance, domestic boilers. This termination consists of a cylinder containing a stack of truncated hollow cones with narrow gap in between and a telescopic tube. The gap between the adjacent cones, and sound-absorbing fibrous material (“Acotherm”) placed in the cavity of these cones produce a low reflection coefficient in the frequency range between 40 and 800 Hz. Longitudinal displacement of these cones inside the cylinder generates a reflection coefficient with magnitude ranging from 0.2 to 0.9. The telescopic tube with an adjustable length (between 0.85 - 1.38 m) allows to achieve a wide range of phases of reflection coefficient. The steps taken to optimize the design and performance of this termination in presence of flame are presented here.
|
|
| 27. |
- Saxena, Vertika, et al.
(författare)
-
Designing variable reflection coefficient for upstream and downstream terminations to study their effect on flame thermoacoustics
- 2022
-
Ingår i: INTERNATIONAL JOURNAL OF SPRAY AND COMBUSTION DYNAMICS. - : SAGE Publications. - 1756-8277 .- 1756-8285. ; 14:3-4, s. 251-265
-
Tidskriftsartikel (refereegranskat)abstract
- In this paper, the design, construction and results of experiments performed on a generic combustion system are presented. The setup is supplemented by various weakly frequency-dependent variable reflection coefficient (RC) devices as upstream and downstream acoustic terminations. The main objective of building such terminations is to provide a method to study burner/flame stability when it is placed between various acoustic configurations (RC: 0.1-0.9) and to determine the figure of merit of a burner based on the evaluation of its map of (in-)stability. Furthermore, burner design parameters such as the burner perforation pattern (holes diameter, pitch, perforation area, etc.) which will provide combustion stability for the widest range of burner's acoustic embedding conditions are identified. The experimental setup comprises of an upstream acoustic termination, a telescopic tube with adjustable length is placed after the upstream termination followed by the burner and the quartz tube. On the top of the quartz tube, the replaceable downstream terminations are installed. Nine downstream terminations are constructed by stacking plates of 0.25 mm thickness separated by spacers ranging from 0.1 to 1 mm thickness. Particularly, for the burners tested in this setup, the smallest hole diameter burner (with the largest perforation area) results in the largest stable region on the stability map in the parameter space. An increase in the flow velocity leads to an increase in the frequency of instability and makes a stable system tend to become unstable, while an increase in the equivalence ratio contributes to stabilizing system instability
|
|
| 28. |
- van den Boom, J.D.B.J, et al.
(författare)
-
Active control of oscillations in a Rijke tube-like flat flame configurations
- 2007
-
Ingår i: Proceeding of the European Combustion Meeting.
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The use of low NOx premixed surface burners with a large modulation range in modern central heating systemsoften to noise problems. In order to make any further advance in the development of these systems the noise problemhas to be solved. Therefore, the possibility of suppression (and stabilization) of these instabilities is in investigatedusing active model-based control strategies. A model for the condensing gas-fired boiler is derived first. based on anacoustic network approach. Special attention is paid to the flame dynamics. Second, a H1 controller is synthesized,where also modelling uncertainties are taken into account. In the end the performance and the robustness of thecontroller is validated during experiments.
|
|
| 29. |
|
|
| 30. |
|
|
| 31. |
|
|
| 32. |
|
|
| 33. |
- Wang, Shuli, et al.
(författare)
-
Effects of exhaust gas recirculation at various loads on diesel engine performance and exhaust particle size distribution using four blends with a research octane number of 70 and diesel
- 2017
-
Ingår i: Energy Conversion and Management. - : Elsevier BV. - 0196-8904. ; 149, s. 918-927
-
Tidskriftsartikel (refereegranskat)abstract
- Partially premixed combustion using gasoline-like fuels on compression ignition engines shows great potentials to break the soot-nitrogen oxides trade off and reduce both emissions simultaneously. By simply adjusting the dilution strategies and injection events, the control of partially premixed combustion is relatively easier compared to other low-temperature combustion concepts. However despite these advantages, recent research shows this concept tends to emit ultra-fine particles. Most previous work on partially premixed combustion only focuses on the soot emissions while the particulate matter in terms of number concentration and size distribution are not well investigated. Ultra-fine particles are dangerous to human health and are getting increasing attentions. Thus the detailed particulate matter emission from partially premixed combustion needs to be further investigated. In this work four gasoline-like ternary fuel blends are designed and experimentally tested under partially premixed combustion. The test blends all share the same two base fuels and blended with different additives. The fuel composition is varied to have the same research octane number. Tests are conducted under different engine loads and dilution strategies since the temperature and oxygen concentration are the key factors in the formation and oxidation of soot. Standard diesel is also tested under the same conditions as a comparison. It is found that these blends are capable of running under partially premixed combustion at low and medium loads and they produce near zero soot emissions when using high exhaust gas recirculation rate. However, these blends do emit smaller particles than diesel under all test loads. Besides, blends with oxygen content yield less soot emissions and smaller particles compared to non-oxygen blends.
|
|
| 34. |
- Yu, J. F., et al.
(författare)
-
Heat transfer and flame stabilization of laminar premixed flames anchored to a heat-flux burner
- 2016
-
Ingår i: International Journal of Hydrogen Energy. - : Elsevier BV. - 0360-3199. ; 41:3, s. 2037-2051
-
Tidskriftsartikel (refereegranskat)abstract
- Measurement of the burning velocity of unstretched laminar hydrogen/air premixed flames suffers from large uncertainties owing to the highly diffusive nature of hydrogen that can give rise to flame instability. This paper reports on a numerical study of the structures and stability of laminar premixed CH4/O2/CO2 flames and H2/O2/N2 flames anchored to a heat-flux burner using a high-order numerical method with detailed chemical kinetic mechanisms and detailed transport properties. The aim is to elucidate the effect of the flow and temperature inhomogeneity generated by the burner plate holes on flame structures and burning velocity. Heat transfer flux between the burner plate and the surrounding gaseous mixture is investigated under various standoff distances and burner plate temperatures. The burning velocity and the detailed flow, temperature and species distributions in flames with a zero net heat flux between the flames and the burner plate are analyzed. It is found that for the methane flames, when the standoff distance is sufficiently small, the burner can essentially suppress the intrinsic flame instability, but the plate holes can give rise to flame wrinkles of the size of the holes. At high standoff distances, the non-uniformity of the flow from the burner plate holes has a minor effect on the flame surface wrinkling; however, large-scale cellular structures can appear on the flame surface due to intrinsic flame instability. For the studied methane flames the effect of non-uniformity of the flow from the burner plate holes on the burning velocity is fairly small. For the studied hydrogen flames the burner plate could not totally suppress the intrinsic flame instability. The intrinsic flame instability can give rise to a significant increase in the flame surface area and mean burning velocity, with more than 25% increase in the burning velocity.
|
|
| 35. |
|
|
| 36. |
- Yu, M., et al.
(författare)
-
Survivability of thermographic phosphors (YAG:Dy) in a combustion environment
- 2010
-
Ingår i: Measurement Science & Technology. - : IOP Publishing. - 0957-0233 .- 1361-6501. ; 21:3
-
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%).
|
|
