| 1. |
- Lövås, Terese, et al.
(författare)
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Development of adaptive kinetics for application in combustion systems
- 2002
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Ingår i: Proceedings of the Combustion Institute. - 1540-7489. ; 29:1, s. 1403-1410
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, an automatic method for reducing chemical mechanisms during run time based on the quasi-steady-state assumption (ASSA) is presented. The method uses a lifetime analysis of the chemical species which can be set to steady state according to a ranking procedure. Steady-state species concentrations are computed by algebraic rather than differential equations, thus yielding a significant reduction in the computational effort. In contrast to previous reduction schemes in which chemical species were selected only when they were in steady state throughout the whole process, the present method allows for species to be selected at each operating point separately generating an adaptive chemical kinetics scheme. The mechanism can change during the simulation run. This ensures that the optimal reduced mechanism is used at each time step leading to a very efficient and accurate procedure. The method is used for calculations of a natural gas fueled engine operating under homogeneous charge compression ignition (hCCI) conditions. We discuss criteria for selecting steady-state species and the influence of these criteria on the results, such as concentration profiles and temperature. A full mechanism with 53 species can be reduced to a minimun of 14 non-steady-state species while still reproducing the physical behavior of the detailed mechanism with good agreement.
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| 2. |
- Nilsson, Per, et al.
(författare)
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Effects of flame stretch and wrinkling on CO formation in turbulent premixed combustion
- 2002
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Ingår i: Proceedings of the Combustion Institute. - 1540-7489 .- 1873-2704. ; 29:2, s. 1873-1879
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Konferensbidrag (refereegranskat)abstract
- This paper presents an investigation of CO formation in a lean premixed propane/air turbulent flame in an afterburner configuration. A previous experiment showed that a high amount of CO was formed in the mean turbulent flame brush. To explain the high CO concentration in the flame zone, the effects of flame stretch and flame wrinkling are studied, based on an ensemble averaged laminar flamelet library approach. It is shown that the flame stretch decreases the laminar burning velocity by 20% under the studied flame conditions, and the stretched flamelet model predicts the non-equilibrium CO concentration in the postflame zone. However, the high CO concentration in the mean flame brush cannot be predicted by a stretched flamelet library model alone. A flamelet model accounting for wrinkled flamelets in the mean turbulent flame brush, and the effect of flame stretch (mainly strain rate), is tested. The model is based on a level-set G-equation for the mean position of the turbulent flame brush and an ensemble average of strained laminar flamelet libraries. A comparison of the numerical results with the experimental data and a previous translating flamelet model clearly shows that the wrinkled flamelet model predicts the intermediate species, such as CO, more accurately. The major species such as O-2 and CO2, as well as temperature, are found to be not sensitive to the flame wrinkling.
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| 3. |
- Ahmed, Ahfaz, et al.
(författare)
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Small ester combustion chemistry : Computational kinetics and experimental study of methyl acetate and ethyl acetate
- 2019
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Ingår i: Proceedings of the Combustion Institute. - : Elsevier BV. - 1540-7489. ; 37:1, s. 419-428
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Tidskriftsartikel (refereegranskat)abstract
- Small esters represent an important class of high octane biofuels for advanced spark ignition engines. They qualify for stringent fuel screening standards and could be synthesized through various pathways. In this work, we performed a detailed investigation of the combustion of two small esters, MA (methyl acetate) and EA (ethyl acetate), including quantum chemistry calculations, experimental studies of combustion characteristics and kinetic model development. The quantum chemistry calculations were performed to obtain rates for H-atom abstraction reactions involved in the oxidation chemistry of these fuels. The series of experiments include: a shock tube study to measure ignition delays at 15 and 30 bar, 1000-1450 K and equivalence ratios of 0.5, 1.0 and 2.0; laminar burning velocity measurements in a heat flux burner over a range of equivalence ratios [0.7-1.4] at atmospheric pressure and temperatures of 298 and 338 K; and speciation measurements during oxidation in a jet-stirred reactor at 800-1100 K for MA and 650-1000 K for EA at equivalence ratios of 0.5, 1.0 and at atmospheric pressure. The developed chemical kinetic mechanism for MA and EA incorporates reaction rates and pathways from recent studies along with rates calculated in this work. The new mechanism shows generally good agreement in predicting experimental data across the broad range of experimental conditions. The experimental data, along with the developed kinetic model, provides a solid groundwork towards improving the understanding the combustion chemistry of smaller esters.
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| 4. |
- Aldén, Marcus
(författare)
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Spatially and temporally resolved laser/optical diagnostics of combustion processes : From fundamentals to practical applications
- 2023
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Ingår i: Proceedings of the Combustion Institute. - : Elsevier BV. - 1540-7489. ; 39:1, s. 1185-1228
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Tidskriftsartikel (refereegranskat)abstract
- Laser diagnostic techniques have for more than five decades been used for gaining a deepened understanding of various combustion processes. The main reason for this is the possibility of non-intrusive measurements of key combustion parameters, e.g. species concentrations, temperatures and velocities, with high spatial and temporal resolution. The present paper will describe some development of the techniques themselves, followed by applications of relevant diagnostic techniques for studies of combustion phenomena and then more applied activities often related to challenges in an industrial environment. The paper is not meant to be a complete review of the entire research field but rather a survey with a majority of the contributions from the author's laboratory. After a short introduction and background (including some historical remarks), some common laser diagnostic techniques will be briefly described. Then some emerging techniques will be described. The first such area to be covered will highlight the use and application of structured illumination through Frequency Recognition Algorithm for Multiple Exposures, FRAME, enabling high speed visualization, 3D imaging and multiple species detection using one standard laser/detector. Furthermore, single ended diagnostics using Scheimpflug LIDAR and backward lasing using short pulse Stimulated Emission will be described and exemplified. In the category of studies of combustion phenomena, the paper will focus on diagnostic challenges and applications when studying combustion of some renewable fuels; solid biomass, ammonia and metals. When studying these fuels, often species not so commonly encountered when using fossil fuels are of interest, e.g. alkali containing species, e.g. KOH, KCl as well as nitrogen bound species, e.g. NH, NH2. In the field of applied diagnostics, preferably in an industrial environment, examples will be given from IC engines, gas turbines as well as full-scale industrial furnaces. In these phenomenological and industrial applications laser-induced fluorescence, Raman scattering and thermographic phosphorescence were mainly utilized, with some examples of photo-fragmentation LIF as well as non-liner techniques, IR-DFWM and CARS. The paper is concluded with a summary and some thoughts about the future.
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| 5. |
- Aldén, Marcus, et al.
(författare)
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Visualization and understanding of combustion processes using spatially and temporally resolved laser diagnostic techniques
- 2011
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Ingår i: Proceedings of the Combustion Institute. - : Elsevier BV. - 1540-7489. ; 33, s. 69-97
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Forskningsöversikt (refereegranskat)abstract
- Laser diagnostic techniques have for more than 30 years added very valuable input for a deepened understanding of combustion processes. The present paper will focus on techniques developed for visualization of important parameters with the ability to get detailed information in space and time. The paper is not meant to be a complete review of the entire research field but rather a survey with a majority of the contributions from the authors' laboratory. After a short introduction and background, essentially three techniques will be highlighted. Planar Laser-Induced Fluorescence, PLIF, will be described in terms of further development directed towards the use of a high-power Alexandrite laser, in some cases yielding a substantially increased sensitivity as compared to the more conventional Nd:YAG and Excimer lasers. There will also be a description of possibilities for high-speed visualization, 3D imaging and the potential to visualize species requiring a two-photon excitation process. Regarding thermometry, the paper will describe and exemplify the use of Thermographic Phosphors, mainly for surface measurements but also in droplets and gas flows. The third area to be described is the use of Polarization Spectroscopy, PS, for spatially and temporally resolved measurements in the IR spectral region, e. g. CO2 and H2O, various hydrocarbons, HCl and HCN. The last chapter focuses on present challenges and future applications. A major challenge is diagnostics in environments with limited optical access. Two methods that are applicable under such conditions are discussed, namely endoscopic approaches and picosecond LIDAR. Another challenging area addressed is application of diagnostics in optically dense environments, e. g. sprays, where a new technique, Structured Laser Illumination Planar Imaging, SLIPI, has been developed for suppressing the influence of multiple scattering. Finally, approaches for measurements of "new" species, challenges associated with LIF quantification, as well as measurements in environments possessing strong background radiation are discussed. (C) 2010 The Combustion Institute. Published by Elsevier Inc. All rights reserved.
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| 6. |
- Allgurén, Thomas, 1986, et al.
(författare)
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Alkali sulfation during combustion of coal in a pilot scale facility using additives to alter the global sulfur to potassium and chlorine to potassium ratios
- 2021
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Ingår i: Proceedings of the Combustion Institute. - : Elsevier BV. - 1540-7489. ; 38:3, s. 4171-4178
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Tidskriftsartikel (refereegranskat)abstract
- Due to the urgent needs to reduce anthropogenic carbon dioxide emissions there is an increasing interest in the use of alternative fuels. For this reason, there is a need for new knowledge on how to design and adapt existing heat and power plants to biogenic and waste-derived fuels. This work relates to co-firing of biomass and coal and the sulfation of alkali chlorides in coal-fired flames doped with chemical additives. We aim to examine the global time scales of alkali sulfation and chlorination based on combustion experiments that were conducted in a 30-kW coal flame. Temperature, gas and particle composition measurements were conducted. Both experiments and modelling support that the apparent alkali sulfation kinetics are fast in a coal-fired flame and that it is dominated entirely by the presence of SO 2. The availability of oxygen and carbon monoxide, or hydrocarbons, is also critical to sustain the sulfation reaction cycle; low concentrations are sufficient. For industrial boilers this implies that sulfur addition, in combination with reburning, should constitute an efficient strategy to mitigate alkali-chlorination and the related high temperature corrosion.
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| 7. |
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| 8. |
- Berglund, Magnus, et al.
(författare)
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LES of supersonic combustion in a scramjet engine model
- 2007
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Ingår i: Proceedings of the Combustion Institute. - : Elsevier BV. - 1540-7489. ; 31, s. 2497-2504
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Tidskriftsartikel (refereegranskat)abstract
- In this study, Large Eddy Simulation (LES) has been used to examine supersonic flow and combustion in a model scramjet combustor. The LES model is based on an unstructured finite volume discretization, using total variational diminishing flux reconstruction, of the filtered continuity, momentum, enthalpy, and passive/reactive scalar equations, used to describe the combustion process. The configuration used is similar to the laboratory scrarmjet at the Institute for Chemical Propulsion of the German Aerospace Center (DLR) and consists of a one-sided divergent channel with a wedge-shaped flameholder at the base of which hydrogen is injected. Here, we investigate supersonic flow with hydrogen injection and supersonic flow with hydrogen injection and combustion. For the purpose of validation, the LES results are compared with experimental data for velocity and temperature at different cross-sections. In addition, qualitative comparisons are also made between predicted and measured shadowgraph images. The LES computations are capable of predicting both the non-reacting and reacting flowfields reasonably well-in particular we notice that the LES model identifies and differentiates between peculiarities of the flowfields found in the experiments. (c) 2006 The Combustion Institute. Published by Elsevier Inc. All rights reserved.
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| 9. |
- Bladh, Henrik, et al.
(författare)
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Optical soot characterization using two-color laser-induced incandescence (2C-LII) in the soot growth region of a premixed flat flame
- 2011
-
Ingår i: Proceedings of the Combustion Institute. - : Elsevier BV. - 1540-7489. ; 33, s. 641-648
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Tidskriftsartikel (refereegranskat)abstract
- The soot growth region of a premixed one-dimensional ethylene/air flame has been investigated using two-color laser-induced incandescence (2C-LII) with focus on optical soot properties. From the 2C-LII technique, primary soot particle sizes were deduced together with the temperature from pyrometry of the laser-heated particles, while the gas temperatures were obtained from pure rotational CARS nitrogen thermometry. Soot particle sizes were also measured from thermophoretically sampled soot particles analyzed by transmission electron microscopy (TEM), and the results showed growing isolated primary soot particles up to a height of 10 mm, after which strong soot aggregation occurred and the increase in soot primary particle size ceased. The measured data was used in the evaluation of the soot absorption function, E(m), and a strong increase by a factor of two was observed from the lowest heights to the highest for assumed constant values of soot density and specific heat at all heights. By comparing the 2C-LII particle sizes with the sizes obtained from TEM, differences were observed. Part of the explanation is that the 2C-LII evaluation did not take aggregation into account, but it is additionally speculated that the thermal accommodation coefficient decreases with height above burner. These results are interesting in view of morphological and composition changes of the soot during the growth process and have implications for the use of 2C-LII as a soot diagnostic technique. (C) 2010 The Combustion Institute. Published by Elsevier Inc. All rights reserved.
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| 10. |
- Bladh, Henrik, et al.
(författare)
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Probing the smallest soot particles in low-sooting premixed flames using laser-induced incandescence
- 2015
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Ingår i: Proceedings of the Combustion Institute. - : Elsevier BV. - 1540-7489. ; 35, s. 1843-1850
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Tidskriftsartikel (refereegranskat)abstract
- In this work we investigate nascent soot particles by analyzing laser-induced incandescence (LII) signals obtained in low-sooting premixed flames. The analysis covers two data sets obtained in separate experimental campaigns. The first data set was obtained in a previous work (Mouton et al., 2013) in methane/oxygen/nitrogen flames (equivalence ratio range 1.95 < Phi < 2.32) at 26.7 kPa, whereas the second was performed in atmospheric ethylene/air flames (1.77 < Phi < 2.00). Both studies show similar trends, i.e. a gradual change of the fluence curves (evolution of the LII signal as function of the laser fluence) from the well-known S-shaped curve for mature soot found at high heights above the burner (HAB) and high equivalence ratio, to a nearly linear behavior for nascent soot found at low HAB and reduced equivalence ratio. With this change comes a decrease in the LII decay time (and hence inferred particle size). Also, this decay time appears to be almost constant with HAB in flames having the lowest equivalence ratio at which the incandescence signal could be detected. In these flames, so-called nucleation flames, the stability of the particle size with HAB suggests that recently nucleated particles have undergone marginal surface growth and coagulation. Existence of such nucleation flames is of great interest for improving the theoretical description of the nucleation step. Experimental results are analyzed by using a theoretical model for LII to determine the particle size evolution throughout the flame at various experimental conditions. We highlight the size difference from nascent soot particles up to mature soot, giving insight into the particle nucleation and the surface growth processes as a function of reaction time and flame conditions. (C) 2014 The Combustion Institute. Published by Elsevier Inc. All rights reserved.
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