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To address the growing need for detailed chemistry in engine simulations, new software tools and validated data sets are being developed under an industry-funded consortium involving members from the automotive and fuels industry. The results described here include systematic comparison and validation of detailed chemistry models using a wide range of fundamental experimental data, and the development of software tools that support the use of detailed mechanisms in engineering simulations. Such tools include the automated reduction of reaction mechanisms for targeted simulation conditions. Selected results are presented and discussed.

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.

Experimental data have been obtained that characterize knock occurrence times and knock intensities in a spark ignition engine operating on indolene and 91 primary reference fuel, as spark timing and inlet temperature were varied. Individual, in-cylinder pressure histories measured under knocking conditions were conditioned and averaged to obtain representative pressure traces. These averaged pressure histories were used as input to a reduced and detailed chemical kinetic model. The time derivative of CO concentration and temperature were correlated with the measured knock intensity and percent cycles knocking. The goal was to evaluate the potential of using homogenous, chemical kinetic models as predictive tools for knock intensity.

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.

A detailed chemical kinetic mechanism was used to simulate the oxidation of n-butane/air mixtures in a motored engine. The modeling results were compared to species measurements obtained from the exhaust of a CFR engine and to measured critical compression ratios. Pressures, temperatures and residence times were considered that are in the range relevant to automotive engine knock. The compression ratio was varied from 6.6 to 15.5 to affect the recycle fraction and the maximum pressure and temperature of the fuel/air mixture. Engine speeds of 600 and 1600 rpm were examined which corresponded to different fuel/air residence times. The relative yields of intermediate species calculated by the model matched the measured yields generally to within a factor of two. The residual fraction derived from the previous engine cycle had a significant impact on the overall reaction rate in the current cycle.

We have studied the chemical aspects of the compression ignition of n-butane experimentally in a spark ignition engine and theoretically using computer simulations with a detailed chemical kinetic mechanism. The results of these studies demonstrate the effect of initial charge composition on autoignition. Experimentally, when the initial charge consisted of 80% fresh charge and 20% recycled products of combustion, we observed that autoignition was inhibited. On the other hand, charging with 80% fresh charge and 20% partial oxidation products from the previous motored cycle resulted in enhanced low-temperature chemistry (with the associated heat release and temperature increase) and autoignition. We assessed how well the detailed kinetic model could predict the autoignition and modified the model to better simulate the experimental observations. We also assessed how chemical preconditioning of the fuel-air charge affected the autoignition process.

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.

A theoretical model has been developed for calculations of the evolution of fuel injected into internal combustion engine chambers. Fuel injection in the form of a gaseous jet and in the form of a liquid droplet spray are considered. The model uses the basic equations of conservation of mass, momentum, and energy in both the gaseous and liquid phases. Applications in two dimensional symmetry of the gaseous jet form of the numerical model are described in stagnant and swirling air flows. The liquid droplet spray model, including coupling between the droplets and the gas phase medium, is described. Applications of the two phase model are described for the case of axially symmetric injection. Finally, the liquid spray model and the gas jet model are applied to the same conditions, leading to a general assessment of the ranges of validity of the gas jet model.