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| 2. |
- Axelsson, Boman
(author)
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Combustion Studies of Soot and Fuel Based on Use of Laser Diagnostics
- 2001
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Doctoral thesis (other academic/artistic)abstract
- In the work described in the present thesis, laser techniques for combustion engine diagnostics were developed and applied. The main techniques were laser-induced incandescence (LII) and laser-induced fluorescence (LIF), used for both flame and engine diagnostics. A novel technique was developed, one in which the relative fuel distribution, as measured by planar laser-induced fluorescence (PLIF), was quantified by means of Raman scattering point measurement. Although the technique showed good potential for laboratory measurements, the limited degree of optical access found in an optical engine suggested further development for engine applications to be feasible. To reduce the need of optical access through windows, an endoscopic detection system was deve-loped and was successfully implemented in an optical engine. Although the transmittance through the endoscopic system was lower than that in normal detection, PLIF measurements of fuel distribution could be made by imaging through the endoscopic detection system. A detailed flame study was performed to evaluate the possibility of using LII for the soot volume fraction and for particle size measurement. Data was compared to those being assessed by extinction-scattering measure-ments. Measured temperature was an important input for determining the primary particle size on the basis of the decay time of the LII signal. The results were encouraging, even with use of the simple decay model employed. The same flame was used to verify the possibility of making simultaneous measurements of extinction and LII, which led to an on-line extinction calibration technique. A three-dimensional representation of the soot volume fraction in a flame was constructed on the basis of eight two-dimensional LII intensity distributions obtained with the use of a Nd:YAG-laser cluster and a high-speed detection system. The LII technique was also applied to engines, where in-cylinder measurements of soot volume fraction were performed in a running direct-injection stratified-charge (DISC) engine. A technique, based on LII, for study of engine-out soot emissions allowing measurements with sub-second temporal resolution during engine transients was evaluated.
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| 3. |
- Axelsson, Boman, et al.
(author)
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Laser-induced incandescence for soot particle size and volume fraction measurements using on-line extinction calibration
- 2001
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In: Applied Physics B. - : Springer Science and Business Media LLC. - 0946-2171 .- 1432-0649. ; 72:3, s. 367-372
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Journal article (peer-reviewed)abstract
- A novel technique for two-dimensional measurements of soot volume fraction and particle size has been developed. It is based on a combined measurement of extinction and laser-induced incandescence using Nd:YAG laser wavelengths of 532 nm and 1064 nm. A low-energy laser pulse at 532 nm was used for extinction measurements and was followed by a more intense pulse at 1064 nm, delayed by 15 ns, for LII measurements. The 532-nm beam was split into a signal beam passing the flame and a reference beam, both of which were directed to a dye cell. The resulting fluorescence signals, from which the extinction was deduced, together with the LII signal, were registered on a single CCD detector. Thus the two-dimensional LII image could be converted to a soot volume fraction map through a calibration procedure during the same laser shot. The soot particle sizes were evaluated from the ratio of the temporal LII signals at two gate time positions. The uncertainty in the particle sizing arose mainly from the low signal for small particles at long gate times and the uncertainty in the flame temperature. The technique was applied to a well-characterized premixed flat flame, the soot properties of which had been previously thoroughly investigated.
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| 4. |
- Axelsson, Boman, et al.
(author)
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Laser-Induced Incandescence for Soot Particle Size Measurements in Premixed Flat Flames
- 2000
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In: Applied Optics. - 2155-3165. ; 39:21, s. 3683-3690
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Journal article (peer-reviewed)abstract
- Measurements of soot properties by means of laser-induced incandescence (LII) and combined scattering–extinction were performed in well-characterized premixed ethylene–air flames. In particular, the possibility of using LII as a tool for quantitative particle sizing was investigated. Particle sizes were evaluated from the temporal decay of the LII signal combined with heat balance modeling of laser-heated particles, and these sizes were compared with the particle sizes deduced from scattering–extinction measurements based on isotropic sphere theory. The correspondence was good early in the soot-formation process but less good at later stages, possibly because aggregation to clusters began to occur. A critical analysis has been made of how uncertainties in different parameters, both experimental and in the model, affect the evaluated particle sizes for LII. A sensitivity analysis of the LII model identified the ambient-flame temperature as a major source of uncertainty in the evaluated particle size, a conclusion that was supported by an analysis based on temporal LII profiles.
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| 6. |
- Brackmann, Christian, et al.
(author)
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Laser-induced fluorescence of formaldehyde in combustion using third harmonic Nd : YAG laser excitation
- 2003
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In: Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy. - 1386-1425. ; 59:14, s. 3347-3356
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Journal article (peer-reviewed)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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| 7. |
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| 8. |
- Hult, Johan, et al.
(author)
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Quantitative three-dimensional imaging of soot volume fraction in turbulent non-premixed flames
- 2002
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In: Experiments in Fluids. - : Springer Science and Business Media LLC. - 1432-1114 .- 0723-4864. ; 33:2, s. 265-269
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Journal article (peer-reviewed)abstract
- A three-dimensional (3-D) imaging system for studies of reactive and non-reactive flows is described. It can be used to reveal the topology of turbulent structures and to extract 3-D quantities, such as concentration gradients. Measurements are performed using a high repetition rate laser and detector system in combination with a scanning mirror. In this study, the system is used for laser-induced incandescence measurements to obtain quantitative 3-D soot volume fraction distributions in both laminar and turbulent non-premixed flames. From the acquired data, iso-concentration surfaces are visualised and concentration gradients calculated.
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| 9. |
- Richter, Mattias, et al.
(author)
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Engine Diagnostics Using Laser Induced Fluorescence Signals Collected Through an Endoscopic Detection System
- 1998
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In: SAE Technical Papers. - 400 Commonwealth Drive, Warrendale, PA, United States : SAE International. - 0148-7191.
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Journal article (peer-reviewed)abstract
- In this paper an alternative method for collecting laser induced fluorescence (LIF) signals from engines with limited optical access is presented. An endoscopic detection system has been used for LIF visualisation of both gaseous and liquid fluids in a DISI-engine. The use of an endoscope made it possible to monitor parts of the combustion chamber that could not be accessed through the piston with conventional optics.Brief investigations of the signal collection efficiency have been performed on the endoscopic system as well as on a system based upon conventional optics.The technique shows promising results and the use of endoscopic detection systems should be considered as a complement to using advance design quarts piston crowns for conventional detection through the piston.
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| 10. |
- Richter, Mattias, et al.
(author)
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Investigation of the Fuel Distribution and the In-Cylinder Flow Field in a Stratified Charge Engine Using Laser Techniques and Comparison with CFD-Modelling
- 1999
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In: SAE Technical Papers. - 400 Commonwealth Drive, Warrendale, PA, United States : SAE International. - 0148-7191.
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Journal article (peer-reviewed)abstract
- This paper presents an investigation of a Volvo Direct Injection Spark Ignition (DISI) engine, where the fuel distribution and the in-cylinder flow field have been mapped by the use of laser techniques in an engine with optical access. Along with the experimental work, CFD-modelling of flow and fuel distribution has been performed.Laser Induced Fluorescence (LIF) visualisation of the fuel distribution in a DI-engine has been performed using an endoscopic detection system. Due to the complex piston crown geometry it was not possible to monitor the critical area around the sparkplug with conventional, through the piston, detection. Therefore, an endoscope inserted in the spark plug hole was used. This approach gave an unrestricted view over the desired area.In addition, the in-cylinder flow fields have been monitored by Particle Image Velocimetry (PIV) through cylinder and piston.The results from both the LIF and the PIV measurements have been compared with CFD-modelling at Volvo. The validation was made at part load when the engine was operating in stratified mode, i.e. late injection during the compression phase. Qualitative agreement was found between the calculated and measured fuel distribution around the spark plug prior to ignition.Also the PIV measurements showed a promising agreement with the flow fields obtained by CFD-modelling. In addition, the transportation properties of the fuel distribution that was monitored by LIF could to a great extent be explained by the results from the PIV measurement and the CFD-modelling.All three techniques showed promising agreements with each other and the measured properties could be used to further increase the accuracy of the CFD-modelling. The close collaboration and comparison between different techniques described in this paper increased the understanding of the processes going on in the combustion chamber.
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| 11. |
- Richter, Mattias, et al.
(author)
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Real-Time Calibration of Planar Laser Induced Fluorescence Air/Fuel-Ration Measurements in Combustion Environments Using in-situ Raman Scattering
- 1998
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In: Symposium (International) on Combustion. - 1540-7489. ; 27:1, s. 51-57
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Journal article (peer-reviewed)abstract
- A laser-based technique for recording absolute air-fuel ratio maps in a single-laser pulse in combustion devices, for instance, prior to ignition in internal combustion engines, is demonstrated. The method is based on an in situ pulse-to-pulse calibration of two-dimensional laser-induced fluorescence (LIF) images of relative fuel distributions by a point Raman measurement. A single excimer laser pulse is used to quasisimultaneously detect planar LIF from a fuel tracer as well as spectrally resolved Raman scattering from oxygen and fuel in one point inside the LIF image plane. By determining the air-fuel ratio in this particular point from the measured Raman signals, the whole LIF image can be scaled, and quantitative two-dimensional air-fuel ratio data can be obtained. In the method, it is crucial to achieve a Raman signal that can be spectrally separated from the much stronger LIF signal. Therefore, the behavior of the Raman signals from air and fuels, like iso-octane and methane, was studied in a cell as well as in a four-stroke spark ignition engine. Especially, spectral interferences from commonly used fluorescent additives (3-pentanone and acetone) with the Raman signals were investigated. Moreover, possibilities for suppressing the background originating from fluorescent tracers by taking advantage of the polarization characteristics of Raman scattering is briefly addressed. Finally, demonstration measurements of the calibration technique are presented, and the precision and accuracy of the method are shortly discussed.
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| 12. |
- Smallwood, Gregory J., et al.
(author)
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Concurrent quantitative laser-induced incandescence and SMPS measurements of EGR effects on particulate emissions from a TDI Diesel engine
- 2002
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In: SAE Technical Papers. - 0148-7191.
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Journal article (peer-reviewed)abstract
- A comparison of scanning mobility particle sizer (SMPS) and laser-induced incandescence (LII) measurements of diesel particulate matter (PM) was performed. The results reveal the significance of the aggregate nature of diesel PM on interpretation of size and volume fraction measurements obtained with an SMPS, and the accuracy of primary particle size measurements by LII. Volume fraction calculations based on the mobility diameter measured by the SMPS substantially over-predict the space-filling volume fraction of the PM. Correction algorithms for the SMPS measurements, to account for the fractal nature of the aggregate morphology, result in a substantial reduction in the reported volume. The behavior of the particulate volume fraction, mean and standard deviation of the mobility diameter, and primary particle size are studied as a function of the EGR for a range of steady-state engine speeds and loads for a turbocharged direct-injection diesel engine. Both the SMPS and LII techniques demonstrate good repeatability and consistency with each other. Increasing the EGR results in a sharp rise in the volume fraction of particulates for all engine speeds and loads. At all speed and load conditions the primary particle size decreases with increasing EGR.
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