| The purpose of this work is to improve our understanding of those factors which affect the ignition quality of a hydrocarbon fuel in a diesel engine. The empirical measure of fuel quality is the cetane number, and the problem is important in Canada because diesel fuel extracted from current domestic sources has a low cetane number.; It is desirable to understand the chemical processes that take place prior to spontaneous ignition in an engine. Since combustion processes involve myriads of reactions, computational analysis is difficult and progress can only be achieved by simplifying the problem. One approach is to use sensitivity analysis, but it often leaves still too many reactions for the problem to be tractable.; An alternative is to use a reduced kinetic model. The work described in this thesis uses one such model proposed by Griffiths in which the reaction mechanism consists of a set of core reactions representing the chemistry at (mainly but not exclusively) higher temperatures and a set of so-called generic reactions. Using this model together with an algorithm that simulates the compression in a diesel engine, ignition delays for a series of hydrocarbons are obtained. This only requires small changes to be made in the rate parameters of the generic reactions, based on the number of H-atoms present in the original fuel molecule.; The effect of structure on ignition delay is explored in some detail. It is shown that for n-paraffins in the diesel fuel boiling range, there is a simple correlation between the ignition delay and the ratio of primary to secondary hydrogen atoms in the molecule. It is also shown that this particular reduced kinetic model accounts successfully for the variation in ignition delay with chain-branching in iso-paraffins, and for the acceleration of ignition in the presence of simple OH-radical sources. |
