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| 2. |
- Fecht, H. -J, et al.
(author)
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Thermophysical properties of liquids : Modelling and non-metallic materials
- 2005
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In: ESA SP. - 0379-6566 .- 1609-0438. ; :1281, s. 24-35
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Journal article (peer-reviewed)abstract
- The accurate knowledge and high-precision measurements of the thermophysical properties of liquids is necessary for the numerical modeling of industrial processes where the solid-liquid phase transformation plays a crucial role. The reduction of magnetic levitation forces in microgravity leads either to a significant improvement in accuracy or makes the measurement possible in the first place. High-precision measurements on chemically highly reactive melts require containerless processing using non-contact diagnostic tools. Scientific precursor experiments were conducted in the TEMPUS containerless processing facility during the Spacelab IML-2 and MSL-1 missions, also.
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| 3. |
- Kiefer, J., et al.
(author)
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OH-thermometry using laser polarization spectroscopy and laser-induced fluorescence spectroscopy in the OH A-X (1,0) band
- 2009
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In: Journal Of Raman Spectroscopy. - : Wiley. - 0377-0486 .- 1097-4555. ; 40:7, s. 828-835
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Conference paper (peer-reviewed)abstract
- Laser-induced fluorescence (LIF) and polarization spectroscopy (PS) is used for OH-thermometry utilizing the off-diagonal A-X (1,0) band. Both techniques are used simultaneously in order to allow a comparison of the results. For deriving temperature information from the spectra, three methods are employed: (1) a contour fit method comparing experimental and calculated spectra, (2) spectral fitting of a single highly resolved spectral line and (3) a two-line intensity ratio approach. In general, both spectroscopic techniques gave similar results. The high-resolution approach (2) did not deliver reasonable results in our experiments. The most accurate but also most time consuming method was the contour fit (1). For future two-dimensional temperature measurements, the 2-line-method (3) was identified to be the method of choice. The present study contains, to the best of our knowledge, the first polarization spectroscopic study in the A-X (1,0) band of OH. Copyright (C) 2009 John Wiley & Sons, Ltd.
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| 4. |
- Brackmann, Christian, et al.
(author)
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Simultaneous vibrational and pure rotational coherent anti-Stokes Raman spectroscopy for temperature and multispecies concentration measurements demonstrated in sooting flames
- 2002
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In: Applied Optics. - 2155-3165. ; 41:3, s. 564-572
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Journal article (peer-reviewed)abstract
- The potential of measuring temperature and multiple species concentrations (N-2, O-2, CO) by use of combined vibrational coherent anti-Stokes Raman spectroscopy (CARS) and pure rotational CARS has been investigated. This was achieved with only one Nd:YAG laser and one dye laser together with a single spectrograph and CCD camera. From measurements in premixed sooting C2H4-air flames it was possible to evaluate temperatures from both vibrational CARS and rotational CARS, spectra, O-2 concentration from the rotational CARS spectra, and CO concentration from the vibrational CARS spectra. Quantitative results from premixed sooting C2H4-air flames are presented, and the uncertainties in the results as well as the possibility of extending the combined CARS technique fur probing of additional species are discussed. (C) 2002 Optical Society of America.
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| 5. |
- Buldyreva, J, et al.
(author)
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Linewidth modelling of C2H2-N-2 mixtures tested by rotational CARS measurements
- 2006
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In: Journal of Raman Spectroscopy. - : Wiley. - 1097-4555 .- 0377-0486. ; 37:6, s. 647-654
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Journal article (peer-reviewed)abstract
- The acetylene-nitrogen system is investigated in a combined theoretical and experimental effort in view of its thermometry applications. Accurate values of the rotational Raman linewidths of acetylene are of crucial importance for the computation of spectra from rotational coherent anti-Stokes Raman scattering (CARS) used for temperature and concentration evaluations. Since the direct measurements of these linewidths are not available, they are rigorously calculated by a semi-classical Robert-Bonamy formalism employing exact trajectories. The computed linewidths are used as input parameters in the theoretical spectra simulation, which is also improved by the inclusion of an interbranch interference with coherent Stokes Raman scattering (CSRS). These theoretical spectra are used to evaluate the temperature from experimental CARS spectra of acetylene-nitrogen mixtures recorded in the pressure range 0.1-0.6 MPa. The new linewidths (NLWs) and the CSRS interference inclusion result in a clear improvement of spectral fitting as well as in reasonable values of evaluated temperatures. Copyright (c) 2006 John Wiley & Sons, Ltd.
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| 6. |
- Kiefer, J., et al.
(author)
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Gas diagnostics by laser-induced breakdown spectroscopy employing polarization filtering
- 2010
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In: Laser Applications to Chemical, Security and Environmental Analysis, LACSEA 2010. - 2162-2701. - 9781557528803
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Conference paper (peer-reviewed)abstract
- In this work we present a setup for laser-induced breakdown spectroscopy (LIBS) employing a polarization filtering approach and use it for gas diagnostics. A one parts-per-million (ppm) detection sensitivity is achieved for hydrogen atoms.
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| 7. |
- Kiefer, J., et al.
(author)
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Laser-induced breakdown spectroscopy in gases using ungated detection in combination with polarization filtering and online background correction
- 2010
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In: Measurement Science & Technology. - : IOP Publishing. - 0957-0233 .- 1361-6501. ; 21:6
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Journal article (peer-reviewed)abstract
- Quantitative and fast analysis of gas mixtures is an important task in the field of chemical, security and environmental analysis. In this paper we present a diagnostic approach based on laser-induced breakdown spectroscopy (LIBS). A polarization filter in the signal collection system enables sufficient suppression of elastically scattered light which otherwise reduces the dynamic range of the measurement. Running the detector with a doubled repetition rate as compared to the laser online background correction is obtained. Quantitative measurements of molecular air components in synthetic, ambient and expiration air are performed and demonstrate the potential of the method. The detection limits for elemental oxygen and hydrogen are in the order of 15 ppm and 10 ppm, respectively.
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| 8. |
- Kiefer, J, et al.
(author)
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Planar laser-induced fluorescence of HCO for instantaneous flame front imaging in hydrocarbon flames
- 2009
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In: Proceedings of the Combustion Institute. - : Elsevier BV. - 1540-7489. ; 32, s. 921-928
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Journal article (peer-reviewed)abstract
- The detection of the formyl radical (HCO) is of great interest in the field of combustion research since it can provide information about the local heat release (HR) rate which is a key parameter in the understanding of combustion processes. Unfortunately, due to the low signal level, HCO planar laser-induced fluorescence (PLTF) has so far not been applicable for single-shot imaging, which is necessary in particular for studying turbulent flames. In the present paper for the first time, to the best of our knowledge, single-shot PLIF imaging of HCO in flames is demonstrated by employing-a multimode frequency-tripled alexandrite laser. Oil the basis of long pulse duration along with a spectrally broad bandwidth enabling multi-line excitation a sufficient signal-to-noise ratio is achieved. In detail, excitation in the B-X system around 258.69 nm is applied and subsequent fluorescence detection in the spectral range 300-400 nm is performed. A series of experiments concerning spectral interferences, saturation behavior and the influence of flame stoichiometry (in the range phi = 0.6-2) have been conducted. Two typical fuels have been employed: methane (CH4) as conventional hydrocarbon as well as dimethyl ether (DME) as modern bio fuel. Single-shot HCO imaging is finally demonstrated in a laminar DME/air Bunsen flame and in a slightly turbulent methane/oxygen welding torch flame. The results indicate that the developed HCO PLIF technique offers a strong potential for improved flame Studies particularly in turbulent flames, In general, the approach to employ laser sources with reasonably broader bandwidth and longer pulse duration compared to conventional Nd:YAG pumped systems for PLIF will open up new possibilities in the field of Combustion diagnostics. (c) 2009 The Combustion Institute. Published by Elsevier file. All rights reserved.
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| 9. |
- Li, Zhongshan, et al.
(author)
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Development of improved PLIF CH detection using an Alexandrite laser for single-shot investigation of turbulent and lean flames
- 2007
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In: Proceedings of the Combustion Institute. - : Elsevier BV. - 1540-7489 .- 1873-2704. ; 31 I, s. 727-735
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Conference paper (peer-reviewed)abstract
- We report on the development of planar laser-induced fluorescence (PLIF) for CH imaging with improved detection sensitivity for single-shot investigations of turbulent, lean, premixed flames. A ringcavity, pulsed Alexandrite laser was frequency-doubled to excite the lines in the R-branch band-head of the B-X (0,0) band and broadband fluorescence from the B-X (0,1), A-X (1,1) and (0,0) bands, overlapping in the spectral range around 431 nm, was collected. The employed Alexandrite laser, which is characterized by its long pulse duration (150 ns), gives a tunable laser beam around 775 nm with a pulse energy for the second harmonic at the CH absorption wavelength of about 70 mJ. Moreover, the laser has the possibility to be operated in narrow bandwidth (100 MHz) or broad bandwidth (8 cm-1). An introductory high resolution excitation scan over the R-branch band-head was performed and, in addition, saturated excitation with the broadband option of the laser was investigated. By simultaneous excitation of several rotational transitions and to bring these transitions close to saturation, high signal-to-noise ratios were reached over a wide range of equivalence ratios. A sharp and thin CH layer was observed in single-shot PLIF images from laminar premixed methane/air flames from Φ = 0.6 to Φ = 1.5. Finally, the impact of the developed CH PLIF technique is demonstrated in a highly turbulent, lean, partially premixed methane/air flame established on a co-axial jet flame burner. © 2006 The Combustion Institute. Published by Elsevier Inc. All rights reserved.
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