Laser spectroscopic investigation of flow fields and NO-formation in a realistic SI engine
This paper presents results from a quantitative character-ization of the NO distribution in a SI engine fueled with a stoichiometric iso-octane/air mixture. Different engine operating conditions were investigated and accurate results on NO concentrations were obtained from essen-tially the whole cylinder for crank angle ranges from igni-tion to the mid expansion stroke. The technique used to measure the two-dimensional NO concentration distribu-tions was laser induced fluorescence utilizing a KrF exci-mer laser to excite the NO A-X (0,2) bandhead. Results were achieved with high temporal and spatial resolution. The accuracy of the measurements was estimated to be 30% for absolute concentration values and 20% for rela-tive values. Images of NO distributions could also be used to evaluate the flame development. Both the mean and the variance of a combustion progress variable could be deduced. The engine used in the investigation was a one cylinder version of a Volvo N1P engine equipped with good optical access. Using the same engine and the same operating conditions, data on the in-cylinder flow field was also obtained using particle imaging velocime-try. The comprehensive and detailed data base generated in the present work is currently being used for detailed vali-dation and improvements of models for numerical simula-tion of engine combustion and emission formation. Nitric oxide is one of the most important combustion gen-erated pollutants with impact on the environment and on human health. Internal combustion engines play a major role in the overall production of this species even though the use of catalytic converters has significantly lowered NO emissions from gasoline engines in recent years. However, in order to reduce emissions even further and to meet future emission regulations, new and improved engines need to be developed. Improved aftertreatment systems and improved engine control will solve part of the problem but lower NO emissions in the raw exhaust would lead to a significant reduction of net emissions, particularly during transients and cold starts. For gasoline engines running with a lean fuel/air mixture special prob-lems are encountered since no satisfactorily efficient aftertreatment system is yet available. Therefore, new developments of the basic combustion system are neces-sary to reduce the amount of NO formed during the energy conversion. These developments would be greatly facilitated by a detailed knowledge of the basic physical and chemical processes in internal combustion engines. This paper presents the application of different laser-based diagnostics for measurements of basic combus-tion phenomena in a commercial gasoline engine
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