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Technical Paper

Development of an Experimental Database and Chemical Kinetic Models for Surrogate Gasoline Fuels

The development of surrogate mixtures that represent gasoline combustion behavior is reviewed. Combustion chemistry behavioral targets that a surrogate should accurately reproduce, particularly for emulating homogeneous charge compression ignition (HCCI) operation, are carefully identified. Both short and long term research needs to support development of more robust surrogate fuel compositions are described. Candidate component species are identified and the status of present chemical kinetic models for these components and their interactions are discussed. Recommendations are made for the initial components to be included in gasoline surrogates for near term development. Components that can be added to refine predictions and to include additional behavioral targets are identified as well. Thermodynamic, thermochemical and transport properties that require further investigation are discussed.
Technical Paper

Detailed Chemical Kinetic Modeling of Diesel Combustion with Oxygenated Fuels

The influence of the addition of oxygenated hydrocarbons to diesel fuels has been studied, using a detailed chemical kinetic model. Resulting changes in ignition and soot precursor production have been examined. N-heptane was used as a representative diesel fuel, and methanol, ethanol, dimethyl ether, dimethoxymethane and methyl butanoate were used as oxygenated fuel additives. It was found that addition of oxygenated hydrocarbons reduced the production of soot precursors. When the overall oxygen content in the fuel reached approximately 30-40 % by mass, production of soot precursors fell effectively to zero, in agreement with experimental studies. The kinetic factors responsible for these observations are discussed.
Technical Paper

An Experimental and Kinetic Modeling Study of the Combustion of n-Butane and Isobutane in an Internal Combustion Engine

Butane is the simplest alkane fuel for which more than a single structural isomer is possible. In the present study, n-butane and isobutane are used in a test engine to examine the importance of molecular structure in determining knock tendency, and the experimental results are interpreted using a detailed chemical kinetic model. A sampling valve was used to extract reacting gases from the combustion chamber of the engine. Samples were withdrawn at different times during the engine cycle, providing concentration histories of a wide variety of reactant, olefin, carbonyl, and other intermediate and product species. The chemical kinetic model predicted the formation of all the intermediate species measured in the experiments. The agreement between the measured and predicted values is mixed and is discussed. Calculations show that RO2 isomerization reactions are more important contributors to chain branching in the oxidation of n-butane than in isobutane.
Technical Paper

The Autoignition of Isobutane in a Knocking Spark Ignition Engine

The chemical aspects of the autoignition of isobutane are studied experimentally in a spark ignition engine and theoretically using computer simulations with a detailed chemical kinetic mechanism. The results of these studies show that even with the relatively knock-resistant fuel, isobutane, there is still a significant amount of fuel breakdown in the end gas with a resulting heat release and temperature increase. The ability of the detailed kinetic model to predict this low temperature chemical activity is assessed and the model is modified to simulate more closely the experimental observations. We address the basic question of whether this first stage of combustion accounts for a chemical preconditioning of the end gas that leads to the autoignition; or whether it merely provides sufficient heat release in the end gas that high temperature autoignition is initiated.