| 1. |
- Hultqvist, Anders, et al.
(författare)
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A Study of the Homogeneous Charge Compression Ignition Combustion Process by Chemiluminescence Imaging
- 1999
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Ingår i: SAE Technical Paper Series. - 400 Commonwealth Drive, Warrendale, PA, United States : SAE International. - 0148-7191.
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Konferensbidrag (refereegranskat)abstract
- An experimental study of the Homogeneous Charge Compression Ignition (HCCI) combustion process has been conducted by using chemiluminescence imaging. The major intent was to characterize the flame structure and its transient behavior. To achieve this, time resolved images of the naturally emitted light were taken. Emitted light was studied by recording its spectral content and applying different filters to isolate species like OH and CH.Imaging was enabled by a truck-sized engine modified for optical access. An intensified digital camera was used for the imaging. Some imaging was done using a streak-camera, capable of taking eight arbitrarily spaced pictures during a single cycle, thus visualizing the progress of the combustion process. All imaging was done with similar operating conditions and a mixture of n-heptane and iso-octane was used as fuel.Some 20 crank angles before Top Dead Center (TDC), cool flames were found to exist. They appear with a faint structure, evenly distributed throughout the combustion chamber. There was no luminosity recorded between the end of cool flames and the start of the main heat release. Around TDC the main heat release starts. Looking at a macro scale, we find that the charge starts to burn simultaneously at arbitrary points throughout the charge. Since the thermal boundary layer is colder than the bulk of the charge, the local heat release is delayed close to the walls. As a result, the total heat release is slowed down. Ensemble averaged 1 images show this wall boundary effect clearly when plotted against CAD. The peak intensity at the main combustion event is one order of magnitude greater than that of the cool flame and the structure is a lot more protruding.Since spontaneous emission imaging is a line-of-sight integration, the flame structure appears a bit smeared. The micro scale structure is very similar from one cycle to another, but there are large variations between cycles on the macro scale.
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| 2. |
- Richter, Mattias, et al.
(författare)
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Engine Diagnostics Using Laser Induced Fluorescence Signals Collected Through an Endoscopic Detection System
- 1998
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Ingår i: SAE Technical Papers. - 400 Commonwealth Drive, Warrendale, PA, United States : SAE International. - 0148-7191.
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Tidskriftsartikel (refereegranskat)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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| 3. |
- Richter, Mattias, et al.
(författare)
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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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Ingår i: SAE Technical Papers. - 400 Commonwealth Drive, Warrendale, PA, United States : SAE International. - 0148-7191.
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Tidskriftsartikel (refereegranskat)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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| 4. |
- Richter, Mattias, et al.
(författare)
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Optical Diagnostics Applied to a Naturally Aspirated Homogeneous Charge Compression Ignition Engine
- 1999
-
Ingår i: SAE Technical Paper Series. - 400 Commonwealth Drive, Warrendale, PA, United States : SAE International. - 0148-7191.
-
Konferensbidrag (refereegranskat)abstract
- Basic optical properties have been investigated in order to characterize the HCCI-combustion process. Basic optical properties of a Homogeneous Charge Compression Ignition (HCCI) engine have been investigated in order to characterize the combustion process. The absorption of light propagating through the combustion chamber has been spectrally resolved for four different fuels. Significant differences between the fuels could be detected. Complementary information could be obtained by recording spontaneous emission of radiation during combustion. Raman point measurements were used to quantify cycle-to-cycle variations of the equivalence ratio. The homogeneity of the charge was monitored by the use of two-dimensional tracer LIF. That method was also utilized to investigate the flame development. The experiments were performed in a six-cylinder, truck-sized engine with one cylinder modified to allow for optical access. The results obtained are believed to be valuable in future applications of optical diagnostics in similar environments.
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| 5. |
- Richter, Mattias, et al.
(författare)
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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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Ingår i: Symposium (International) on Combustion. - 1540-7489. ; 27:1, s. 51-57
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Tidskriftsartikel (refereegranskat)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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