| 1. |
- Afzelius, Mikael, et al.
(författare)
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Pure rotational coherent anti-Stokes Raman spectroscopy in mixtures of CO and N-2
- 2004
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Ingår i: Applied Optics. - 2155-3165. ; 43:36, s. 6664-6672
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Tidskriftsartikel (refereegranskat)abstract
- We present a model for quantitative measurements in binary mixtures of nitrogen and carbon monoxide by the use of dual-broadband rotational coherent anti-Stokes Raman spectroscopy. The model has been compared with experimental rotational coherent anti-Stokes Raman scattering spectra recorded within the temperature range of 294-702 K. Temperatures and concentrations were evaluated by spectral fits using libraries of theoretically calculated spectra. The relative error of the temperature measurements was 1-2%, and the absolute error of the CO concentration measurements was <0.5% for temperatures less than or equal to600 K. For higher temperatures, the gas composition was not chemically stable, and we observed a conversion of CO to CO2. The influence of important spectroscopic parameters such as the anisotropic polarizability and Raman line-broadening coefficients are discussed in terms of concentration measurements. In particular, it is shown that the CO concentration measurement was more accurate if N-2-CO and CO-N-2 line-broadening coefficients were included in the calculation. The applicability of the model for quantitative flame measurements is demonstrated by measuring CO concentrations in ethylene/air flames. (C) 2004 Optical Society of America.
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| 2. |
- Bood, Joakim, et al.
(författare)
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Multipoint temperature and oxygen-concentration measurements using rotational coherent anti-Stokes Raman spectroscopy
- 2000
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Ingår i: Optics Letters. - 0146-9592. ; 25:20, s. 1535-1537
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Tidskriftsartikel (refereegranskat)abstract
- A novel technique for coherent anti-Stokes Raman spectroscopy (CARS) measurements in multiple points is presented. With a system of cylindrical lenses, each laser beam is split into several focused beams, yielding separate planar boxcars configurations. Spectrally resolved CARS signals are detected at different heights on the CCD chip. With dual-broadband rotational CARS the setup is demonstrated for quantitative measurements of temperature- and oxygen-concentration profiles. The technique was demonstrated for three points only, but it can be extended to more points by use of special optics; this choice must be based on a sufficient signal-to-noise ratio in all points for the actual measurement condition.
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| 3. |
- Brackmann, Christian
(författare)
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Development and Application of Rotational Coherent Anti-Stokes Raman Spectroscopy and Laser-induced Fluorescence for Combustion Diagnostics
- 2004
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The thesis concerns the development and application of two laser-based methods for combustion diagnostics: dual broadband rotational coherent anti-Stokes Raman spectroscopy (CARS) and laser-induced fluorescence (LIF). In efforts to increase the usefulness of the CARS technique, the applicability of a method involving a combination of the rotational CARS technique and the closely related vibrational CARS technique was investigated. In addition an extension of the rotational CARS technique such that not only single-point but also multiple-points measurements could be performed was presented. The rotational CARS technique was also used in an experimental investigation of a dimethyl ether (DME)-air diffusion flame for determining temperatures and relative oxygen concentrations. The major combustion application of the rotational CARS technique taken up in the thesis was its use for temperature measurements in an internal combustion engine operated under knocking combustion conditions. Temperature measurements were performed at different locations within the combustion chamber and at different points in time during the engine cycle. The insights these measurements provided, both concerning the experimental application of the rotational CARS technique in engines and in the evaluation of the measured data, were summarized in a review paper. The work with the LIF technique presented in the thesis involved primarily studies of formaldehyde, CH2O. Spectroscopic investigations of CH2O using excitation at a wavelength of 355 nm were carried out in laboratory flames. Laser-induced fluorescence by use of 355 nm excitation was also employed for measurements of formaldehyde in internal combustion engines. Measurements in a spark ignition engine involving two consecutive LIF measurements being performed within a given engine cycle provided data that could be used for determining the flame propagation within the combustion chamber. The characterization of the DME diffusion flame referred to above also included measurements of formaldehyde by use of the LIF technique, particular attention being directed at obtaining a qualitatively correct profile of the formaldehyde concentration in the flame by adjusting the measured signal to take account of quenching and temperature dependence. The laser-induced fluorescence technique was also used to investigate the devolatilisation of wood particles, a process representing the first step in the combustion of solid fuel of this type. The studies carried out included measurements of absorption and of both spectral and imaging LIF. The multi-species composition of the products emitted, hydrocarbon compounds in particular, resulted for both the absorption and the spectral LIF measurements in spectral signatures without distinct features, making identification of specific species difficult. Formaldehyde, which could be identified from the measured spectra was an exception to this. The imaging LIF measurements also provided some information on the flow of the emitted volatiles in relation to the internal wood fibre structure.
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| 4. |
- Brackmann, Christian, et al.
(författare)
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Laser-induced fluorescence of formaldehyde in combustion using third harmonic Nd : YAG laser excitation
- 2003
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Ingår i: Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy. - 1386-1425. ; 59:14, s. 3347-3356
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Tidskriftsartikel (refereegranskat)abstract
- Formaldehyde (CH2O) is an important intermediate species in combustion processes and it can through laser-induced fluorescence measurements be used for instantaneous flame front detection. The present study has focussed on the use of the third harmonic of a Nd:YAG laser at 355 nm as excitation wavelength for formaldehyde, and different dimethyl ether (C2H6O) flames were used as sources of formaldehyde in the experiments. The investigations included studies of the overlap between the laser profile and the absorption lines of formaldehyde, saturation effects and the potential occurrence of laser-induced photochemistry. The technique was applied for detection of formaldehyde in an internal combustion engine operated both as a spark ignition engine and as a homogenous charge compression ignition engine. (C) 2003 Elsevier B.V. All rights reserved.
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| 5. |
- Brackmann, Christian, et al.
(författare)
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Optical and mass spectrometric study of the pyrolysis gas of wood particles
- 2003
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Ingår i: Applied Spectroscopy. - : SAGE Publications. - 1943-3530 .- 0003-7028. ; 57:2, s. 216-222
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Tidskriftsartikel (refereegranskat)abstract
- A detailed experimental investigation has been made of the pyrolysis-the first step in biomass combustion-of single birchwood particles. In addition to mass spectrometric and gravimetric analysis, the pyrolysis volatiles were characterized by different optical techniques. Absorption measurements showed a nearly featureless absorption in the ultraviolet spectral region with a continuously stronger absorption for shorter wavelengths. Using different excitation wavelengths, laser-induced fluorescence measurements revealed generally broad spectra in the spectral region from 300-500 nm, which are characteristic spectral signatures for larger hydrocarbons. The optical data were monitored at different times in the pyrolysis process of the particles and compared with the results from the mass spectrometric and gravimetric analysis. The sensitivity of the optical techniques for differentiation between specific molecules was rather low, although formaldehyde could be observed both in absorption and fluorescence spectra. Laser-induced fluorescence measurements were also made for two-dimensional visualization of the pyrolysis volatiles; emitted from heated birchwood particles, indicating much higher flows along the fiber direction than across.
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| 6. |
- Brackmann, Christian, et al.
(författare)
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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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Ingår i: Applied Optics. - 2155-3165. ; 41:3, s. 564-572
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Tidskriftsartikel (refereegranskat)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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| 7. |
- Brackmann, Christian, et al.
(författare)
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Thermometry in internal combustion engines via dual-broadband rotational coherent anti-Stokes Raman spectroscopy
- 2004
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Ingår i: Measurement Science & Technology. - 0957-0233. ; 15:3, s. 13-25
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Forskningsöversikt (refereegranskat)abstract
- Rotational coherent anti-Stokes Raman spectroscopy (CARS) has since the beginning of the 1980s been developed as a non-intrusive tool for temperature measurements in combustion. Since the introduction of the dual-broadband concept in 1986, the quality of the technique has been much improved, and application to practical combustion situations facilitated. Since the first demonstration of its use in spark-ignition engines in 1993, several measurement campaigns in engines have been accomplished. These campaigns concerned temperature measurements in the unburned gas mixture before combustion as part of a larger project with the aim of improving the knowledge on the phenomenon of engine knock. In this paper, the results of this work are reviewed with a focus on the characteristics of the technique and the quality of the evaluated temperatures. Re-evaluations of data using an improved theoretical model are presented and compared with previous results. Moreover, the treatment of large data sets on single shots from spatial regions with conditions varying from unburned to burned gas is discussed. It is demonstrated that dual-broadband rotational CARS probing nitrogen and oxygen has a high potential for thermometry at the conditions in the unburned gas mixture. Merits and limitations of the technique are discussed and the issues treated are, among others, experimental problems, data evaluation, and single-shot temperature accuracy.
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| 8. |
- Grandin, Börje, et al.
(författare)
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A study of the influence of exhaust gas recirculation and stoichiometry on the heat release in the end-gas prior to knock using rotational coherent anti-Stokes-Raman spectroscopy thermometry
- 2002
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Ingår i: International Journal of Engine Research. - : SAGE Publications. - 1468-0874 .- 2041-3149. ; 3:4, s. 209-221
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Tidskriftsartikel (refereegranskat)abstract
- Heat release in the end-gas prior to autoignition was investigated using different experimental methods including transducers for heat flux and pressure as well as rotational coherent anti-Stokes-Raman spectroscopy, which is a laser-based method for non-intrusive instantaneous thermometry of the gas. The time history was examined in the cases of mixtures of various stoichio-metries, where some were diluted with exhaust gas recir-culation (EGR). The measured temperature history was compared with the isentropic temperature calculated from the cylinder pressure trace. This comparison revealed a difference in heat release from low-temperature reactions in the end-gas for the various mixtures tested at a constant indicated mean effective pressure and a fixed position of 50 per cent burnt charge. It is shown that lean mixtures tend to exhibit the highest knock intensity, mainly due to a decrease in specific heat, as compared to the richer mixtures, which result in an earlier knock onset and as a consequence higher knock intensity. Furthermore, the comparison of temperatures indicates that the rich mixtures have a high heat release from low-temperature chemistry, which to some extent negates the higher specific heat of the charge. As a consequence, a slight enrichment of the charge can lead to higher knock intensity in comparison with a stoichiometric mixture. In spite of the lower specific heat of the charge when a stoichiometric charge was diluted with cooled EGR, these mixtures showed a very low tendency to knock.
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| 9. |
- Grandin, Börje, et al.
(författare)
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Heat Release in the End-Gas Prior to Knock in Lean, Rich and Stoichiometric Mixtures With and Without Egr
- 2002
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Ingår i: SAE Technical Papers. - 0148-7191.
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Tidskriftsartikel (refereegranskat)abstract
- SI Engine knock is caused by autoignition in the unburnt part of the mixture (end-gas) ahead of the propagating flame. Autoignition of the end-gas occurs when the temperature and pressure exceeds a critical limit when comparatively slow reactions - releasing moderate amounts of heat - transform into ignition and rapid heat release. In this paper the difference in the heat released in the end-gas - by low temperature chemistry - between lean, rich, stochiometric, and stoichiometric mixtures diluted with cooled EGR was examined by measuring the temperature in the end-gas with Dual Broadband Rotational CARS. The measured temperature history was compared with an isentropic temperature calculated from the cylinder pressure trace. The experimentally obtained values for knock onset were compared with results from a two-zone thermodynamic model including detailed chemistry modelling of the end-gas reactions.
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| 10. |
- Grandin, Börje, et al.
(författare)
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The effect of knock on the heat transfer in an SI engine : Thermal boundary layer investigation using CARS temperature measurements and heat flux measurements
- 2000
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Ingår i: SAE Technical Papers. - 400 Commonwealth Drive, Warrendale, PA, United States : SAE International. - 0148-7191.
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Konferensbidrag (refereegranskat)abstract
- It is generally accepted that knocking combustion influences the heat transfer in SI engines. However, the effects of heat transfer on the onset of knock is still not clear due to lack of experimental data of the thermal boundary layer close to the combustion chamber wall. This paper presents measurements of the temperature in the thermal boundary layer under knocking and non-knocking conditions. The temperature was measured using dual-broadband rotational Coherent anti-Stokes Raman Spectroscopy (CARS). Simultaneous time-resolved measurements of the cylinder pressure, at three different locations, and the heat flux to the wall were carried out. Optical access to the region near the combustion chamber wall was achieved by using a horseshoe-shaped combustion chamber with windows installed in the rectangular part of the chamber. This arrangement made CARS temperature measurements close to the wall possible and results are presented in the range 0.1-5 mm from the wall. The engine was run with constant fuel flow under near stoichiometric conditions. Knocking and non-knocking conditions were achieved by using different mixtures of n-heptane and iso-octane.
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