| 1. |
- Kagan, L., et al.
(författare)
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Detonation initiation by a hot corrugated wall
- 2007
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Ingår i: Proceedings of the Combustion Institute. - : Elsevier BV. - 0082-0784 .- 1878-027X .- 1540-7489. ; 31, s. 2415-2420
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Tidskriftsartikel (refereegranskat)abstract
- A numerical simulation of premixed gas combustion spreading from a hot corrugated wall is performed. It is found that sufficiently deep corrugations may trigger an abrupt transition from deflagrative to detonative combustion. The effect is found to be highly sensitive to the flame's normal speed and the reaction rate pressure dependence, favoring fast flames and high-order reactions.
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| 2. |
- Gashi, S, et al.
(författare)
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Curvature and wrinkling of premixed flame kernels - comparisons of OHPLIF and DNS data
- 2005
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Ingår i: Symposium (International) on Combustion. - : Elsevier BV. - 0082-0784. ; 30, s. 809-817
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Tidskriftsartikel (refereegranskat)abstract
- The effects of curvature and wrinkling on the growth of turbulent premixed flame kernels have been investigated using both 2D OH planar laser-induced fluorescence (PLIF) and 3D direct numerical simulation (DNS). Comparisons of results between the two approaches show a high level of agreement, providing confidence in the simplified chemistry treatment employed in the DNS, and indicating that chemistry may have only a limited influence on the evolution of the freely propagating flame. This is in contrast to previous studies of the very early flame development where chemistry may be dominant. Statistics for curvature and wrinkling are presented in the form of probability density functions, and there is good agreement with previous findings. The limitations of 2D PLIF measurements of curvature are quantified by comparison with full 3D information obtained from the DNS. The usefulness of PLIF in providing data over a wide parameter range is illustrated using statistics obtained from both CH4/air and H-2/air mixtures, which show a markedly different behaviour due to their different thermo-diffusive properties. The results provide a demonstration of the combined power of PLIF and DNS for flame investigation. Each technique is shown to compensate for the weaknesses of the other and to reinforce the strengths of both.
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| 3. |
- Hult, Johan, et al.
(författare)
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Experimental analysis of local flame extinction in a turbulent jet diffusion flame by high repetition 2-D laser techniques and multi-scalar measurements
- 2005
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Ingår i: Symposium (International) on Combustion. - : Elsevier BV. - 0082-0784. ; 30:1, s. 701-709
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, we present a detailed experimental study of turbulence chemistry interactions in the "DLR_B" turbulent jet diffusion flame. The flame operates on mixtures of CH4, H-2, and N-2 in the fuel stream at Re = 22,800 and is a target flame within the TNF workshop. Extinction and re-ignition events can be tracked in real time and related to the underlying flow field phenomena and temperature fields. Time resolved measurements of OH radical concentration fields are performed in combination with temperature and velocity field measurements. For this purpose, we combined high repetition rate (33 kHz) PLIF imaging with stereoscopic PIV and double pulse Rayleigh imaging techniques. Comparisons are made with results from multi-scalar Raman/Rayleigh/LIF point measurements that reveal the thermochemical state of the flame. The large deviations from equilibrium observed on resulting OH/temperature joint pdfs could be related to strain rate and Damkohler number variations caused by turbulent flow structures leading to frequent extinctions. The 2D measurement series uniquely reveal the underlying mechanism that can lead to such events. Finally, comparisons are made to strained laminar flame calculations, which are generally found to be in good agreement with the measured data. (c) 2004 The Combustion Institute.
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| 4. |
- Kohse-Hoinghaus, K, et al.
(författare)
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Combustion at the focus: laser diagnostics and control
- 2005
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Ingår i: Symposium (International) on Combustion. - : Elsevier BV. - 0082-0784. ; 30:1, s. 89-123
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Tidskriftsartikel (refereegranskat)abstract
- Fifty years after the foundation of the Combustion Institute and almost 150 years after Michael Faraday's famous lectures on the combustion of a candle, combustion diagnostics have come a long way from visual inspection of a flame to detailed analysis of a combustion process with a multitude of sophisticated techniques, often using lasers. The extended knowledge on combustion phenomena gained by application of these diagnostic techniques, combined with equally advanced numerical simulation of the process, has been instrumental in designing modern combustion devices with efficient performance and reduced pollutant emission. Also, similar diagnostic techniques are now employed to develop sensors for process control in combustion. This article intends to give a perspective on the potential of combustion diagnostics by highlighting selected application examples and by guiding the reader to recent literature. In particular, techniques are emphasized, which permit measurement of important features of the chemical composition, sometimes in conjunction with flow field parameters. Although a complete image of present research and applications in combustion diagnostics and control is beyond the scope of this article, this overview may be a starting place where ideas may be found to solve specific combustion problems with the aid of diagnostics.
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| 5. |
- Vestin, Fredrik, et al.
(författare)
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Dual-broadband rotational CARS thermometry in the product gas of hydrocarbon flames
- 2005
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Ingår i: Symposium (International) on Combustion. - : Elsevier BV. - 0082-0784. ; 30:1, s. 1673-1680
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Tidskriftsartikel (refereegranskat)abstract
- Coherent anti-Stokes Raman spectroscopy (CARS) is an established technique for gas-phase thermometry in combustion. In this work, rotational CARS in the dual-broadband approach has been investigated for flame thermometry in the product gas of ethylene/air flames in a wide range of equivalence ratios (0.5 < phi < 2.5). The nitrogen lines dominated the rotational CARS spectra in the whole equivalence range, but for fuel-lean flames also oxygen lines gave significant spectral contributions. Therefore, the temperature evaluation was based on spectral fitting of both nitrogen and oxygen. Product gas species such as carbon dioxide, water, carbon monoxide, and hydrogen contribute to the non-resonant susceptibility of the gas and influence the nitrogen and oxygen linewidths through collisions. In this work, the main focus was on the influence of these collisions on the nitrogen and oxygen Raman linewidths and consequently the evaluated temperature in the product gas of flames. In the range of studied equivalence ratios with various amounts of different product gas species, the evaluated temperature was raised up to 45 K when including broadening from CO2, H2O, and CO on the measured nitrogen and oxygen lines. It was also concluded that H2O was the main contributor in all non-sooting flames. The influence of the non-resonant susceptibility in the spectral evaluation is discussed, and its coupling to the inclusion of the line broadening from product gas species as well. It has thus been shown that line-broadening effects from product gas species are highly important for quantitative rotational CARS thermometry in flames. (c) 2004 The Combustion Institute.
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