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Combustion reactions and thermokinetic data

Numerical models, which reveal the role of oxygen-containing additives, like methyl tert butyl ether (MTBE), in the formation of pollutants from automobile engine combustion, have been developed and validated through this project.

The combustion models formulated consist of two parts. The first describes all atypical reaction mechanisms which have been individually established and subsequently published. These reaction mechanisms are known as the CO-C4 reaction kernel. Their rates are specific and are not deducible from other reactions, and therefore must be measured individually. The second part of the model contains the typical C5-C8 reaction mechanisms. These are all alike and can therefore be reduced to a small number of elementary reaction mechanisms by applying a number of well-defined analogy rules. This numerical simulation of a combustion process starts by initializing a group of primary propagation radicals and radicals of the C0-C4 kernel. The C5-C8 oxidation reactions are then generated with computer software, by using the aforementioned analogy rules. During the calculations, the reactant mixture evolves with time to yield the final combustion products. The model reaction schemes were then validated by comparing the model's predictions with experimental data. The combustion models were then validated against experiments using a wide range of pressure, temperature and equivalence ratios encountered in engine operating conditions. The validation experiments from literature consisted of n-heptane oxidation, iso-octane oxidation and MTBE oxidation.

The tools developed have provided extended chemical mechanisms, thermodynamic data and kinetic rates that are necessary to describe the combustion of complex molecules or blends for in-engine conditions. These include software tools which automatically generate linear and branched hydrocarbon oxidation kinetic mechanisms and associated thermokinetic data up to C8. The agreement between the model prediction and experimental observation was satisfactory.

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