| 1. |
- Abou-Taouk, Abdallah, 1982, et al.
(författare)
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Optimized Reduced Chemistry and Molecular Transport for Large Eddy Simulation of Partially Premixed Combustion in a Gas Turbine
- 2016
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Ingår i: Combustion Science and Technology. - : Informa UK Limited. - 0010-2202 .- 1563-521X. ; 188:1, s. 21-39
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Tidskriftsartikel (refereegranskat)abstract
- A methodology is discussed to automatically determine the parameters of closed budget equations for chemical species mass fractions and energy, in order to simulate spatially filtered flames as required in large eddy simulation (LES). The method accounts for the effects of LES filtering on chemistry and transport by simultaneously optimizing, for a reduced number of species, the Arrhenius reaction rates and a correction to mixture-averaged molecular diffusion coefficients. The objective is to match, for a given filter size, spatially filtered canonical one-dimensional flames simulated with detailed chemistry solutions. This approach is designed for quite well-resolved LES, in which most of the unresolved fluctuations result from flame thickening due to spatial filtering, thus featuring weak levels of sub-grid scale flame wrinkling. Methane-air partially premixed combustion is addressed. A four-step reduced reaction mechanism involving seven species is developed along with mass and heat molecular transport properties. The optimization is performed at atmospheric pressure and at 3 bar, for ranges of fresh gas temperatures [300–650 K] and equivalence ratios [0.4–1.2]. Comparisons with the filtered detailed chemistry solution of a planar propagating front show that the laminar flame speed, the adiabatic flame temperature, the species profiles in the reaction zone, and the flow chemical composition and temperature at equilibrium are adequately predicted. The new sub-grid scale modeling approach is then applied to three-dimensional LES of an industrial gas turbine burner. Good agreement is found between the quantities predicted with LES and experimental data, in terms of flow and flame dynamics, axial velocities, averaged temperatures, and some major species concentrations. Results are also improved compared to previous simulations of the same burner.
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| 2. |
- Alekseev, Vladimir, et al.
(författare)
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Experimental Uncertainties of the Heat Flux Method for Measuring Burning Velocities
- 2016
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Ingår i: Combustion Science and Technology. - : Informa UK Limited. - 1563-521X .- 0010-2202. ; 188:6, s. 853-894
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Tidskriftsartikel (refereegranskat)abstract
- The laminar burning velocity is a fundamental property of combustiblemixtures important for kinetic model validation as well as for practicalapplications. Many efforts are directed towards its accurate determination.The heat flux method is one of the commonly recognized methodsfor measuring laminar burning velocity, however, the information on theaccuracy of the method is scattered in the literature. In the present work,an attempt wasmade to summarize and extend the available informationon the different factors contributing to the experimental uncertainty ofthe heat flux method. Experimental setup of the Lund University group,typical for the heat flux community, and the procedures used to determinethe burning velocity are described. Furthermore, the influence ofdifferent uncertainty factors, originating from each part of the setup, isanalyzed. Asymmetric heat fluxes and the method for determining flamesurface area were found to give an important contribution to the totalerror. As a result of this, some of the previously published data have beenre-evaluated. Finally, recommendations are presented on how to controlor reduce the uncertainties in the heat flux measurements, and possibledirections for future research, aimed at improvement of the accuracy andunderstanding of the method, are outlined.
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| 3. |
- Bengtsson, Per Erik, et al.
(författare)
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C2 Production and Excitation in Sooting Flames using Visible Laser Radiation : Implications for Diagnostics in Sooting Flames
- 1991
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Ingår i: Combustion Science and Technology. - : Informa UK Limited. - 0010-2202 .- 1563-521X. ; 77:4-6, s. 307-318
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Tidskriftsartikel (refereegranskat)abstract
- Swan band emission of C2. which had been produced and excited (d3∏x←a 3∏u, Δ v = 0) by focused, tunable, visible laser radiation, was studied in sooting ethylene flames. The C2signal from the sooting regions of the flames was found to be proportional to the measured volume fractions of soot, indicating laser-vaporized soot to be the source of the signal, and as such it can be used as a diagnostic tool for point measurements of the volume fraction of soot. C2emission was detected for all incident wavelengths between 485 and 540 nm, with a C2signal 1–2 orders of magnitude higher when the wavelength was tuned to a C2 resonance than when tuned to a wavelength between the Swan bands. High concentrations of laser-produced C2 and emission from C2Swan bands can, through interference effects, limit the applicability of laser diagnostic techniques to sooting flames.
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| 4. |
- Bengtsson, Per Erik, et al.
(författare)
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Rotational cars thermometry in sooting flames
- 1992
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Ingår i: Combustion Science and Technology. - : Informa UK Limited. - 0010-2202 .- 1563-521X. ; 81:1-3, s. 129-140
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Tidskriftsartikel (refereegranskat)abstract
- Coherent anti-Stokes Raman scattering of pure rotational transitions, rotational CARS, is demonstrated as an efficient method for temperature determination in sooting flames. The dual broadband CARS approach was used to measure temperature profiles in premixed, sooting ethylene flames at atmospheric pressure by probing the nitrogen gas. The recorded spectra were of equally high quality in non-sooting and sooting flames with volume fractions of soot of up to 7 x 10 7 cm3 soot/cm3The advantages of rotational CARS in comparison with several other techniques for the measurement of temperatures in sooting flames, and the general applicability of the technique to different combustion conditions, are discussed. Potential limitations in the application of rotational CARS to sooting flames that are more heavily sooting than the ones investigated in this study, are outlined.
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| 5. |
- Berard, L., et al.
(författare)
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Compounds Produced by the Pyrolysis of Powders and Dusts Present in the Alimentary Industry
- 2023
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Ingår i: Combustion Science and Technology. - : Taylor and Francis Ltd.. - 0010-2202 .- 1563-521X. ; 195:3, s. 419-
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Tidskriftsartikel (refereegranskat)abstract
- Under certain conditions dust explosions occur in the alimentary industry. Following ATEX and other guidelines have not eliminated accidents. Therefore, more knowledge is needed. The current work delivers experimental results describing phase transitions and decomposition of dusts. Dusts from wheat flour, chili powder, corn starch, milk powder, cocoa powder, and by-product of grain are investigated. The temperature of pyrolisation has been identified using TGA to be in the range [250°C, 600°C] in air and [300°C, 450°C] in nitrogen. It was found that the compositions of the pyrolysis gases depend on temperature. Carbon monoxide, carbon dioxide, methane, and hydrogen were the main contributors to the pyrolysis gases. The distributions are described with a polynomial or Gaussian fit. The current paper proposes coefficients for Gaussian polynomials expressing the concentration for the four primary pyrolysis gases.
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| 6. |
- Brackmann, Christian, et al.
(författare)
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Quantitative measurements of species and temperature in a DME-air counterflow diffusion flame using laser diagnostic methods
- 2006
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Ingår i: Combustion Science and Technology. - : Informa UK Limited. - 1563-521X .- 0010-2202. ; 178:6, s. 1165-1184
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Tidskriftsartikel (refereegranskat)abstract
- A diffusion flame of dimethyl ether (DME) and air in a counterflow burner has been investigated experimentally by means of different laser-based methods. Quantitative measurements of temperature, O-2 concentration, and OH concentration have been carried out using dual broadband rotational coherent anti-Stokes Raman Spectroscopy (CARS), Rayleigh scattering and laser-induced fluorescence (LIF). Furthermore a qualitative formaldehyde profile has been measured using LIF. The measured profile has been compensated for fluorescence signal quenching and the Boltzmann distribution to obtain a representative qualitative formaldehyde profile for the flame.
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| 7. |
- Brackmann, C., et al.
(författare)
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Strategies for Quantitative Planar Laser-Induced Fluorescence of NH Radicals in Flames
- 2016
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Ingår i: Combustion Science and Technology. - : Informa UK Limited. - 0010-2202 .- 1563-521X. ; 188:4-5, s. 529-541
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Tidskriftsartikel (refereegranskat)abstract
- Laser-induced fluorescence imaging of the NH radical using excitation in the (0-0) and (1-0) vibrational bands of the A3Π-X3Σ– electronic transition is characterized in premixed NH3-air flames. Filtered detection for excitation of the (1-0) band is found to be beneficial for measurement conditions with a challenging background and/or interferences. Concentration evaluation for excitation in the (0-0) and (1-0) bands is feasible by means of fully or partially saturated fluorescence, respectively. Detection limits of a few tens of ppm for averaged data and 100 ppm on a single-shot basis was achieved for 3-cm imaging size using both excitation alternatives. Thinning and broadening of the NH layer in a turbulent flame indicate turbulence/flame chemistry coupling, which occurred at lower turbulence levels compared with hydrocarbon combustion. Fluorescence imaging of the NH flame-front marker in such flames thus provide an experimental configuration for detailed studies of turbulence/flame chemistry interactions.
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| 8. |
- Bychkov, Vitaly, et al.
(författare)
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Gas compression moderates flame acceleration in deflagration-to-detonation transition
- 2012
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Ingår i: Combustion Science and Technology. - : Informa UK Limited. - 0010-2202 .- 1563-521X. ; 184:7-8, s. 1066-1079
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Tidskriftsartikel (refereegranskat)abstract
- The effect of gas compression at the developed stages of flame acceleration in smooth-wall and obstructed channels is studied. We demonstrate analytically that gas compression moderates the acceleration rate, and we perform numerical simulations within the problem of flame transition to detonation. It is shown that flame acceleration undergoes three distinctive stages: (1) initial exponential acceleration in the incompressible regime, (2) moderation of the acceleration process due to gas compression, so that the exponential acceleration state goes over to a much slower one, (3) eventual saturation to a steady (or statistically steady) high-speed deflagration velocity, which may be correlated with the Chapman-Jouguet deflagration speed. The possibility of deflagration-to-detonation transition is demonstrated.
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| 9. |
- Bychkov, Vitaly, et al.
(författare)
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On the Theory of Turbulent Flame Velocity
- 2007
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Ingår i: Combustion Science and Technology. - : Informa UK Limited. - 0010-2202 .- 1563-521X. ; 179:1&2, s. 137-151
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Tidskriftsartikel (refereegranskat)abstract
- The renormalization ideas of self-similar dynamics of a strongly turbulent flame front are applied to the case of a flame with realistically large thermal expansion of the burning matter. In that case a flame front is corrugated both by external turbulence and the intrinsic flame instability. The analytical formulas for the velocity of flame propagation are obtained. It is demonstrated that the flame instability is of principal importance when the integral turbulent length scale is much larger than the cutoff wavelength of the instability. The developed theory is used to analyze recent experiments on turbulent flames propagating in tubes.
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| 10. |
- Chan, Y. L., et al.
(författare)
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The Comparative and Combined Effects of Nitric Oxide and Higher Alkanes in Sensitizing Methane Oxidation
- 2012
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Ingår i: Combustion Science and Technology. - : Informa UK Limited. - 1563-521X .- 0010-2202. ; 184:1, s. 114-132
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Tidskriftsartikel (refereegranskat)abstract
- The comparative and combined effects of nitric oxide (NO) and higher alkanes on methane oxidation were examined by experimentation and kinetic modeling. Experiments were conducted using fuel-lean, lower-alkanes mixtures with NO (0-400 ppm v/v) in an atmospheric flow reactor at residence time of 2 s over the temperature range of 820-950 K. NO was found to greatly promote methane conversion, and its sensitizing effect strengthened with the increasing concentration that was added to the system. The promoting effect of higher alkanes on methane conversion was also evident, particularly at zero or low NO concentrations. A strong dependency of the sensitizing effect on the concentration of higher alkanes present was also observed. The kinetic mechanism from Le Cong et al., performed reasonably well in reproducing the experimental trends. However, the sensitizing propensity of higher alkanes in the presence of NO could not be unambiguously ranked under all conditions. Modification to the kinetic mechanism of Le Cong et al., was attempted. Specifically, the submechanism of C(3) peroxy radicals was added, but the modeling results indicated a lower impact on methane conversion than was initially expected. The most sensitive reactions were revealed, and the generalized reaction pathways for methane oxidation sensitized by higher alkanes, with or without the presence of NO, were also proposed, following detailed sensitivity analysis.
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