| 1. |
- Afzelius, Mikael, et al.
(author)
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Exact treatment of classical trajectories governed by an isotropic potential for linewidth computations
- 2004
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In: Molecular Physics. - : Informa UK Limited. - 1362-3028 .- 0026-8976. ; 102:16-17, s. 1759-1765
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Journal article (peer-reviewed)abstract
- Two models for exact classical trajectories in the field of an isotropic potential are investigated for the purpose of semiclassical linebroadening calculations. The first directly uses the exact solution of the classical equation of motion. The second starts from the equation of motion and computes the trajectory by numerical solution of the differential equations. In the framework of both models, all the computations are performed numerically, thus allowing the use of refined ab initio potential energy surfaces. For the example of the linebroadening of pure nitrogen and carbon monoxide, it is shown that, owing to the dominant short-range forces in these self-perturbed molecular systems, the limiting case corresponding to traditional parabolic trajectories can be used without any important loss of precision.
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| 2. |
- Afzelius, Mikael, et al.
(author)
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Pure rotational coherent anti-Stokes Raman spectroscopy in mixtures of CO and N-2
- 2004
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In: Applied Optics. - 2155-3165. ; 43:36, s. 6664-6672
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Journal article (peer-reviewed)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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| 3. |
- Afzelius, Mikael
(author)
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Rotational Coherent Anti-Stokes Raman Spectroscopy: Experimental and Theoretical Developments in Gas-phase Thermometry
- 2004
-
Doctoral thesis (other academic/artistic)abstract
- Dual-broadband pure rotational coherent anti-Stokes Raman spectroscopy was investigated in terms of thermometry and species concentration measurement for studies of combustion. The modelling of rotational CARS spectra under conditions of high pressure at room temperature was investigated. Resonant terms of the Stokes (CSRS) type were found to have a significant effect on the intensity of the anti-Stokes (CARS) branch, the effect increasing in strength with an increase in pressure. Taking account of this inter-branch interference effect improved the accuracy of temperature measurement under conditions of high pressure. An experimental study of the statistical precision of temperature measurements showed the precision to improve with use of a single-mode rather than a multi-mode Nd:YAG laser, a decrease in standard deviation by a factor of two or more being observed. Further investigation linked the measurement precision to the intensity noise observed in the CARS spectra. Temperature measurements in the post-flame zone of ethylene/air flames were conducted with the aim of studying the impact on temperature measurements of the collisional line widths employed in the model. Taking account of the line broadening of the species CO, CO2 and H2O was found to increase the evaluated temperature by 20-47 K. Spectra recorded in ethylene/air flames revealed the spectral signatures of N2, O2, CO and CO2, the spectrum of nitrogen always being strongest. The potential of rotational CARS for species concentration measurements under such conditions was also investigated. A model for binary mixtures of N2 and CO that was developed was tested for concentration measurements in these flames. The measured CO concentrations agreed closely with theoretical calculations. The collisional line broadening of Raman spectral lines in mixtures of N2 and CO was studied theoretically by means of semiclassical Robert-Bonamy calculations. The self-broadening of nitrogen (N2-N2) in particular was investigated, employing the ab initio intermolecular potential PES8. The major objective was to calculate CO-N2 and N2-CO line broadening. Use of the line widths obtained resulted in more accurate CO concentration measurements in binary mixtures of CO and N2 by use of rotational CARS.
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| 4. |
- Afzelius, Mikael, et al.
(author)
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Semiclassical calculations of collision line broadening in Raman spectra of N-2 and CO mixtures
- 2004
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In: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 120:18, s. 8616-8623
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Journal article (peer-reviewed)abstract
- We present a detailed theoretical study of pressure-broadened Raman line shapes in binary mixtures of nitrogen and carbon monoxide. The semiclassical Robert-Bonamy theory was used to calculate self-broadened Q-branch linewidths of N-2 and CO, and Lennard-Jones (LJ) potential energy surface parameters were fixed by comparing our results with extensive experimental linewidth data. For the case of N-2, the ab initio PES8 potential energy surface was investigated, however, the anisotropic repulsive part had to be reduced to ensure a good agreement with experimental linewidths. The agreement between calculations and experiments was remarkably good, both for self-broadened N-2 and CO Q-branch linewidths. Yet, our calculations were not able to predict the experimentally observed difference between Q- and S-branch linewidths of self-broadened N-2. The central results of this work are the Q-branch linewidths of N-2-CO and CO-N-2, which have been calculated through an extrapolation of the parameters of the potential energy surfaces used for self-broadened linewidths by common combination rules. (C) 2004 American Institute of Physics.
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| 5. |
- Brackmann, Christian, et al.
(author)
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Thermometry in internal combustion engines via dual-broadband rotational coherent anti-Stokes Raman spectroscopy
- 2004
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In: Measurement Science & Technology. - 0957-0233. ; 15:3, s. 13-25
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Research review (peer-reviewed)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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| 6. |
- Li, Zhongshan, et al.
(author)
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Applications of a single-longitudinal-mode alexandrite laser for diagnostics of parameters of combustion interest
- 2004
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In: Review of Scientific Instruments. - : AIP Publishing. - 1089-7623 .- 0034-6748. ; 75:10, s. 3208-3215
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Journal article (peer-reviewed)abstract
- We report on the applications of a single-longitudinal-mode (SLM) pulsed alexandrite laser system for diagnostics of parameters of flow/combustion interest. The laser system is characterized by its narrow linewidth, high peak power, and broad tunablity. The absolute frequency of the laser output was monitored by a wavelength diagnostic system, which included a high-resolution confocal etalon and a molecular iodine laser-induced fluorescence (LIF) detection system. Different nonlinear frequency conversion schemes were used to cover a large frequency range from the infrared to the deep UV. The versatility of the laser system for flow/combustion diagnostics is demonstrated in three applications, namely filtered Rayleigh scattering, high-resolution Doppler-free two-photon LIF of CO, and infrared LIF and polarization spectroscopy of CO2. The potential impacts of using this SLM laser system in laser flow/combustion diagnostic applications are discussed. (C) 2004 American Institute of Physics.
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| 7. |
- Roy, S, et al.
(author)
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Dual-pump dual-broadband coherent anti-Stokes Raman scattering in reacting flows
- 2004
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In: Optics Letters. - 0146-9592. ; 29:16, s. 1843-1845
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Journal article (peer-reviewed)abstract
- A dual-pump, dual-broadband coherent anti-Stokes Raman scattering system for simultaneous measurements of temperature and concentrations of N-2, O-2, and CO2 in reacting flows is demonstrated. In this system pure rotational transitions of N-2-O-2 and rovibrational transitions of N-2-CO2 are probed simultaneously with two narrowband pump beams, a broadband pump beam, and a broadband Stokes beam. The main advantage of this technique is that it permits accurate temperature measurements at both low and high temperatures as well as concentration measurements of three molecules. (C) 2004 Optical Society of America.
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