The Effects of Charge Non-Uniformity on Autoignition in a Gas Fuelled Motored Engine 1999-01-1179

The effects of charge non-uniformity on autoignition of methane/air mixtures in a motored engine are investigated analytically using a varying global kinetic data model derived from the results of a detailed chemical kinetic scheme under similar conditions in a simple adiabatic constant volume reactor. These derived varying global kinetic data model was implemented in the CFD KIVA-3 code. The relative contribution of fluid motion generated by piston motion, heat transfer, chemical reactivity of the cylinder charge and swirl movement to the inhomogeneities in the properties of the cylinder charge and their consequent effects on the evolution of the autoignition process are presented and discussed. The results demonstrate that the adiabatic homogeneous core temperature and the homogeneous bulk mean temperature assumptions, often used in the chemical kinetic calculations for autoignition and knock studies in engines, are inadequately representative of the engine environment, even for adiabatic conditions. The results also confirm that to neglect such inhomogeneities within the engine cylinder charge will produce serious errors in the prediction of the onset of autoignition in an engine environment, the calculation of reaction rates and derivation of chemical kinetic data from motored engine studies.