A Diagnostic Multizone Zero-Dimensional Model for SI Engine with Chemical Kinetics

A comprehensive multizone zero-dimensional diagnostic model is presented for a spark ignition engine cycle. It considers the charge to be made up of two zones, burnt products and unburnt reactants, both under the same, time varying pressure. For each crank angle increment during combustion, a new distinct zone of burnt products is created. It does not exchange mass and heat with the rest of the charge and undergoes a series of continuously varying, yet distinctly different thermochernical processes. The model computes the rate of heat release and other thermochemical properties of all the zones from measured pressure crank angle data obtained from an instrumented engine. A thermochemical sub-model which predicts the properties of the unburnt and burnt gases during the combustion and expansion, as well as the chemical energy release during exothermic process, was developed. Low temperature preflame reactions and high temperature chemical reactions are described via a chemical kinetic mechanism composed by combining several already validated detailed mechanisms. The formation of NOx was assumed to follow the extended Zeldovich mechanism.

The application of the model is illustrated by the performance analysis of two-cylinder 700cc SI engine, at two differents speeds. The particular emphasis was placed upon the formation of major combustion generated pollutants, NOx and CO, measured in a real engine and calculated by the model. The results of calculations are in a satisfactory agreement with the basic engine characteristics as far the absolute values of parameters and trends of changes are concerned.