scientific use of the technique is for characterization of the earth's atmosphere. Basically... more scientific use of the technique is for characterization of the earth's atmosphere. Basically, a laser beam, usually from a pulsed laser, is directed towards the region of interest, where it interacts with the medium under investigation. By detecting the backscattered radiation, the laser/matter interaction may be analyzed and some properties of the medium penetrated by the laser beam can be determined. The range resolution is directly proportional to the laser pulse duration: ΔR = c⋅Δt/2, where ΔR is the range resolution, c the speed of light, and Δt the pulse duration. Traditionally pulse durations on the order of 10 ns have been used in most LIDAR applications, resulting in range resolution on the order of 1 meter. Obviously, the range resolution may be vastly improved using ultra-short laser pulses in the picosecond range. With a range resolution in the mm-range the technique would be interesting for combustion research. Another attractive feature is that it is a single-ended technique, i.e. only one optical access (an opening or a window) is required on the device to be investigated. Hence, ps-LIDAR may be applicable in extremely challenging environments such as power plants with limited optical access or in large fires. In an ongoing research project, a ps-LIDAR system using laser pulses of typically 30 ps duration, from a mode- locked Nd:YAG laser, is developed. Using such short pulses, a range resolution of 5 mm is achievable. With a basic experimental setup, collecting the backscattered radiation using a lens system, the method has been characterized and successfully demonstrated for species concentration measurements 1 . Currently a new LIDAR receiver based on a Newtonian telescope is about to be implemented in the experimental setup. With this receiver the system will be improved in terms of light collection efficiency, flexibility, and robustness. The main task of the present Master project is to experimentally characterize the ps-LIDAR system with the new receiver installed. Description The goal of the project is to characterize the ps-LIDAR system with the new receiver incorporated in the setup. LIDAR-signals from ambient air should be recorded for a variety of system settings, such as different positions for the primary telescope mirror, different slit widths and streak rates of the streak camera, and different laser wavelengths (266, 355, and 532 nm). Ultimately, all data should be collected in a well-structured data base, containing detailed information about experimental conditions for each recorded LIDAR trace. The project should be carried out in the following way (major steps). Firstly, a project plan should be made. Secondly, a measurement matrix outlining the various conditions/settings to be investigated should be determined and documented. The third step constitutes the major part of the project, and that is to perform the measurements outlined in the measurement matrix. If there is time for it, a few measurements in a flame may be carried out as well. The final step is to document the work in a scientific report, i.e. writing the Master thesis.
We apply cavity-enhanced frequency modulation absorption spectroscopy (also known as NICE-OHMS) t... more We apply cavity-enhanced frequency modulation absorption spectroscopy (also known as NICE-OHMS) to perform highly sensitive high-resolution spectroscopy of the sixth overtone band of NO near 797 nm. Our spectrometer provides a sensitivity corresponding to a minimum detectable absorption coefficient of 2.5×10-10 cm-1Hz-1/2, which is ~80 times worse than the ideal shot-noise limited sensitivity. Line intensities are measured for the R(7.5), R(9.5), and R(10.5) rovibrational lines in the 2Π 1/2- 2Π1/2 sub-band. From these line intensities we calculate a total vibrational band intensity of 2.2×10-6 cm-2atm-1 (at 296 K) and a vibrational transition dipole moment of 4.1 μDebye. The measured values are estimated to be accurate to within +/-25%.
We applied cavity-enhanced frequency modulation absorption spectroscopy (also known as noise-immu... more We applied cavity-enhanced frequency modulation absorption spectroscopy (also known as noise-immune cavity-enhanced optical heterodyne molecular spectroscopy) to perform high-resolution spectroscopy of the sixth overtone band of nitric oxide near 797 nm. By using novel high-bandwidth balanced detectors, baseline variations caused by residual amplitude modulation were significantly reduced. The ultrahigh sensitivity (2 x 10(-10) cm(-1) minimum detectable absorption at 1 Hz detection bandwidth) of our spectrometer allowed accurate measurements of 15 individual line intensities of P- and R-branch transitions in the 2Pi(1/2)-2Pi(1/2) subband. A vibrational transition moment of 3.09(6) muD+/-13% and Herman-Wallis coefficients of a = -0.0078(26) and b = 0.001 25(45) were found by fitting the line intensities. Based on our measured transition moment, and those of other transitions from the literature, a new parametrization for the electric dipole moment function (EDMF) of nitric oxide, valid for 0.91 < or = r < or = 1.74 A, has been extracted. The residuals of this fit demonstrate that the derived EDMF is the most accurate representation to date of the dipole moment function. The new EDMF will be valuable for accurate intensity prediction of transitions that cannot be easily measured experimentally.
Optical characteristics of dimethyl ether (DME) are presented, with emphasis on laser-based combu... more Optical characteristics of dimethyl ether (DME) are presented, with emphasis on laser-based combustion diagnostics. DME is a well-known substance which has excellent properties as fuel for compression ignition (CI) engines. It is also believed to have suitable properties for laser diagnostics in CI engines, but reports of its optical properties are sparse in the literature. DME has therefore been investigated
... CHRISTIAN BRACKMANN* JOAKIM BOOD MARCUS ALDE´ N ... a study in a laboratory flame is the work... more ... CHRISTIAN BRACKMANN* JOAKIM BOOD MARCUS ALDE´ N ... a study in a laboratory flame is the work by Harrington and Smyth (1993), which has been followed by more publications (Paul and Najm, 1998; Bombach and Käppeli, 1999; Klein-Douwel et al., 2000; Böckle et al ...
Laser diagnostic techniques have for more than 30years added very valuable input for a deepened u... more Laser diagnostic techniques have for more than 30years added very valuable input for a deepened understanding of combustion processes. The present paper will focus on techniques developed for visualization of important parameters with the ability to get detailed information in space and time. The paper is not meant to be a complete review of the entire research field but rather
... Division of Combustion Physics, Lund University, Box 118, 221 00 Lund, Sweden E-mail:billy.ka... more ... Division of Combustion Physics, Lund University, Box 118, 221 00 Lund, Sweden E-mail:billy.kaldvee@forbrf.lth.se. Received 3 May 2011, in final form 5 September 2011 Published 19 October 2011 Online at stacks.iop.org/MST/22/125302 ...
The decay of OH concentration following photolysis of room-temperature vapor-phase hydrogen perox... more The decay of OH concentration following photolysis of room-temperature vapor-phase hydrogen peroxide is studied as a function of photolysis fluence at 266 nm in an open air environment. The rate of decay is found to increase with increasing photolysis fluence, i.e., with increasing number of photodissociated H2O2(g) molecules. Single-exponential functions approximate the OH concentration decay rather well, even for higher photolysis levels, and the decay time is shown to be inversely proportional to the H2O2(g) concentration. For fluences of about 450 mJ/cm2 the difference between a single-exponential decay and measured data is becoming evident after approximately 150 μs. Calculations based on a chemical kinetics model agree well with experimental data also for times >150 μs. By combining the model with measurements, the actual photolysis levels used in experiments are estimated. The best fit between measured data and the model suggests that about 1.1% of the H2O2(g) molecules are dissociated with a photolysis fluence of ∼450 mJ/cm2, in reasonable agreement with a Beer–Lambert based estimation. Excitation scans did not unfold any differences between OH spectra recorded at different photolysis fluences.
Imaging of vapor-phase H2O2 concentrations is performed using photofragmentation LIF. An Nd:YAG-l... more Imaging of vapor-phase H2O2 concentrations is performed using photofragmentation LIF. An Nd:YAG-laser is used for photolysis and a dye laser for LIF on OH generated in the photolysis process. Detection limit is ~30 ppm.
Pure rotational coherent anti-Stokes Raman scattering (CARS) experiments have been performed in a... more Pure rotational coherent anti-Stokes Raman scattering (CARS) experiments have been performed in acetylene for temperatures ranging from 294 to 582 K, and in mixtures of acetylene and nitrogen in the mole fraction range of 0.06–0.32 for acetylene at room temperature. The experimental spectra are evaluated by a least-square fitting to libraries of theoretically calculated spectra using two different Raman linewidth models, one with and one without dependence on the rotational quantum number J. It is found that a J-dependent model is favourable, both regarding temperature measurements in pure acetylene, and simultaneous acetylene concentration and temperature measurements in different mixtures of acetylene and nitrogen. For the temperature measurements performed in pure acetylene the temperature inaccuracy is generally less than 2% when the J-dependent model for the Raman linewidths is used. It is found that fitting the value of the non-resonant susceptibility significantly improves the quality of the spectral fits and is a requirement for high temperature accuracy with the present model. The evaluated concentrations show a maximum error of 13% on a relative scale. Potential sources of systematical errors both regarding measured temperatures and acetylene concentrations are discussed.
The potential of measuring temperature and multiple species concentrations (N2, O2, CO) by use of... more The potential of measuring temperature and multiple species concentrations (N2, O2, 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, O2 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 for probing of additional species are discussed.
Rotational coherent anti-Stokes Raman spectroscopy (CARS) is a well-established spectroscopic tec... more Rotational coherent anti-Stokes Raman spectroscopy (CARS) is a well-established spectroscopic technique for thermometry at pre-combustion temperatures and atmospheric pressure. However, at pressures of several MPa, a previous investigation revealed large discrepancies between experimental data and the theoretical model. A re-evaluation has been made of these data (at room temperature and in the range 1.5–9 MPa) with two improvements to the spectral code. The first is the inclusion of an inter-branch interference effect, which is described in detail in Paper I. The second is the use of experimental S1-branch Raman line widths measured at 295 K, with a temperature dependence extracted from semi-classical calculations following the Robert–Bonamy formalism. It is shown that these two modifications significantly improve the theoretical model, since both the spectral fits and the accuracy of the evaluated temperatures are considerably improved.
scientific use of the technique is for characterization of the earth's atmosphere. Basically... more scientific use of the technique is for characterization of the earth's atmosphere. Basically, a laser beam, usually from a pulsed laser, is directed towards the region of interest, where it interacts with the medium under investigation. By detecting the backscattered radiation, the laser/matter interaction may be analyzed and some properties of the medium penetrated by the laser beam can be determined. The range resolution is directly proportional to the laser pulse duration: ΔR = c⋅Δt/2, where ΔR is the range resolution, c the speed of light, and Δt the pulse duration. Traditionally pulse durations on the order of 10 ns have been used in most LIDAR applications, resulting in range resolution on the order of 1 meter. Obviously, the range resolution may be vastly improved using ultra-short laser pulses in the picosecond range. With a range resolution in the mm-range the technique would be interesting for combustion research. Another attractive feature is that it is a single-ended technique, i.e. only one optical access (an opening or a window) is required on the device to be investigated. Hence, ps-LIDAR may be applicable in extremely challenging environments such as power plants with limited optical access or in large fires. In an ongoing research project, a ps-LIDAR system using laser pulses of typically 30 ps duration, from a mode- locked Nd:YAG laser, is developed. Using such short pulses, a range resolution of 5 mm is achievable. With a basic experimental setup, collecting the backscattered radiation using a lens system, the method has been characterized and successfully demonstrated for species concentration measurements 1 . Currently a new LIDAR receiver based on a Newtonian telescope is about to be implemented in the experimental setup. With this receiver the system will be improved in terms of light collection efficiency, flexibility, and robustness. The main task of the present Master project is to experimentally characterize the ps-LIDAR system with the new receiver installed. Description The goal of the project is to characterize the ps-LIDAR system with the new receiver incorporated in the setup. LIDAR-signals from ambient air should be recorded for a variety of system settings, such as different positions for the primary telescope mirror, different slit widths and streak rates of the streak camera, and different laser wavelengths (266, 355, and 532 nm). Ultimately, all data should be collected in a well-structured data base, containing detailed information about experimental conditions for each recorded LIDAR trace. The project should be carried out in the following way (major steps). Firstly, a project plan should be made. Secondly, a measurement matrix outlining the various conditions/settings to be investigated should be determined and documented. The third step constitutes the major part of the project, and that is to perform the measurements outlined in the measurement matrix. If there is time for it, a few measurements in a flame may be carried out as well. The final step is to document the work in a scientific report, i.e. writing the Master thesis.
We apply cavity-enhanced frequency modulation absorption spectroscopy (also known as NICE-OHMS) t... more We apply cavity-enhanced frequency modulation absorption spectroscopy (also known as NICE-OHMS) to perform highly sensitive high-resolution spectroscopy of the sixth overtone band of NO near 797 nm. Our spectrometer provides a sensitivity corresponding to a minimum detectable absorption coefficient of 2.5×10-10 cm-1Hz-1/2, which is ~80 times worse than the ideal shot-noise limited sensitivity. Line intensities are measured for the R(7.5), R(9.5), and R(10.5) rovibrational lines in the 2Π 1/2- 2Π1/2 sub-band. From these line intensities we calculate a total vibrational band intensity of 2.2×10-6 cm-2atm-1 (at 296 K) and a vibrational transition dipole moment of 4.1 μDebye. The measured values are estimated to be accurate to within +/-25%.
We applied cavity-enhanced frequency modulation absorption spectroscopy (also known as noise-immu... more We applied cavity-enhanced frequency modulation absorption spectroscopy (also known as noise-immune cavity-enhanced optical heterodyne molecular spectroscopy) to perform high-resolution spectroscopy of the sixth overtone band of nitric oxide near 797 nm. By using novel high-bandwidth balanced detectors, baseline variations caused by residual amplitude modulation were significantly reduced. The ultrahigh sensitivity (2 x 10(-10) cm(-1) minimum detectable absorption at 1 Hz detection bandwidth) of our spectrometer allowed accurate measurements of 15 individual line intensities of P- and R-branch transitions in the 2Pi(1/2)-2Pi(1/2) subband. A vibrational transition moment of 3.09(6) muD+/-13% and Herman-Wallis coefficients of a = -0.0078(26) and b = 0.001 25(45) were found by fitting the line intensities. Based on our measured transition moment, and those of other transitions from the literature, a new parametrization for the electric dipole moment function (EDMF) of nitric oxide, valid for 0.91 < or = r < or = 1.74 A, has been extracted. The residuals of this fit demonstrate that the derived EDMF is the most accurate representation to date of the dipole moment function. The new EDMF will be valuable for accurate intensity prediction of transitions that cannot be easily measured experimentally.
Optical characteristics of dimethyl ether (DME) are presented, with emphasis on laser-based combu... more Optical characteristics of dimethyl ether (DME) are presented, with emphasis on laser-based combustion diagnostics. DME is a well-known substance which has excellent properties as fuel for compression ignition (CI) engines. It is also believed to have suitable properties for laser diagnostics in CI engines, but reports of its optical properties are sparse in the literature. DME has therefore been investigated
... CHRISTIAN BRACKMANN* JOAKIM BOOD MARCUS ALDE´ N ... a study in a laboratory flame is the work... more ... CHRISTIAN BRACKMANN* JOAKIM BOOD MARCUS ALDE´ N ... a study in a laboratory flame is the work by Harrington and Smyth (1993), which has been followed by more publications (Paul and Najm, 1998; Bombach and Käppeli, 1999; Klein-Douwel et al., 2000; Böckle et al ...
Laser diagnostic techniques have for more than 30years added very valuable input for a deepened u... more Laser diagnostic techniques have for more than 30years added very valuable input for a deepened understanding of combustion processes. The present paper will focus on techniques developed for visualization of important parameters with the ability to get detailed information in space and time. The paper is not meant to be a complete review of the entire research field but rather
... Division of Combustion Physics, Lund University, Box 118, 221 00 Lund, Sweden E-mail:billy.ka... more ... Division of Combustion Physics, Lund University, Box 118, 221 00 Lund, Sweden E-mail:billy.kaldvee@forbrf.lth.se. Received 3 May 2011, in final form 5 September 2011 Published 19 October 2011 Online at stacks.iop.org/MST/22/125302 ...
The decay of OH concentration following photolysis of room-temperature vapor-phase hydrogen perox... more The decay of OH concentration following photolysis of room-temperature vapor-phase hydrogen peroxide is studied as a function of photolysis fluence at 266 nm in an open air environment. The rate of decay is found to increase with increasing photolysis fluence, i.e., with increasing number of photodissociated H2O2(g) molecules. Single-exponential functions approximate the OH concentration decay rather well, even for higher photolysis levels, and the decay time is shown to be inversely proportional to the H2O2(g) concentration. For fluences of about 450 mJ/cm2 the difference between a single-exponential decay and measured data is becoming evident after approximately 150 μs. Calculations based on a chemical kinetics model agree well with experimental data also for times >150 μs. By combining the model with measurements, the actual photolysis levels used in experiments are estimated. The best fit between measured data and the model suggests that about 1.1% of the H2O2(g) molecules are dissociated with a photolysis fluence of ∼450 mJ/cm2, in reasonable agreement with a Beer–Lambert based estimation. Excitation scans did not unfold any differences between OH spectra recorded at different photolysis fluences.
Imaging of vapor-phase H2O2 concentrations is performed using photofragmentation LIF. An Nd:YAG-l... more Imaging of vapor-phase H2O2 concentrations is performed using photofragmentation LIF. An Nd:YAG-laser is used for photolysis and a dye laser for LIF on OH generated in the photolysis process. Detection limit is ~30 ppm.
Pure rotational coherent anti-Stokes Raman scattering (CARS) experiments have been performed in a... more Pure rotational coherent anti-Stokes Raman scattering (CARS) experiments have been performed in acetylene for temperatures ranging from 294 to 582 K, and in mixtures of acetylene and nitrogen in the mole fraction range of 0.06–0.32 for acetylene at room temperature. The experimental spectra are evaluated by a least-square fitting to libraries of theoretically calculated spectra using two different Raman linewidth models, one with and one without dependence on the rotational quantum number J. It is found that a J-dependent model is favourable, both regarding temperature measurements in pure acetylene, and simultaneous acetylene concentration and temperature measurements in different mixtures of acetylene and nitrogen. For the temperature measurements performed in pure acetylene the temperature inaccuracy is generally less than 2% when the J-dependent model for the Raman linewidths is used. It is found that fitting the value of the non-resonant susceptibility significantly improves the quality of the spectral fits and is a requirement for high temperature accuracy with the present model. The evaluated concentrations show a maximum error of 13% on a relative scale. Potential sources of systematical errors both regarding measured temperatures and acetylene concentrations are discussed.
The potential of measuring temperature and multiple species concentrations (N2, O2, CO) by use of... more The potential of measuring temperature and multiple species concentrations (N2, O2, 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, O2 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 for probing of additional species are discussed.
Rotational coherent anti-Stokes Raman spectroscopy (CARS) is a well-established spectroscopic tec... more Rotational coherent anti-Stokes Raman spectroscopy (CARS) is a well-established spectroscopic technique for thermometry at pre-combustion temperatures and atmospheric pressure. However, at pressures of several MPa, a previous investigation revealed large discrepancies between experimental data and the theoretical model. A re-evaluation has been made of these data (at room temperature and in the range 1.5–9 MPa) with two improvements to the spectral code. The first is the inclusion of an inter-branch interference effect, which is described in detail in Paper I. The second is the use of experimental S1-branch Raman line widths measured at 295 K, with a temperature dependence extracted from semi-classical calculations following the Robert–Bonamy formalism. It is shown that these two modifications significantly improve the theoretical model, since both the spectral fits and the accuracy of the evaluated temperatures are considerably improved.
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