Measured and Predicted Particle Number and Mass Emissions from Spark-Ignition Engines

Modern engine technologies are subject to increasingly tighter emission standards and recent number-based regulations have become a new challenge, since historically only a mass-based regulation needed to be met. This evolution derives from the need to control the emissions of very fine particles, that are believed to cause more damage than larger ones. The aim of the present work is to provide further guidance in understanding the mechanisms of particle emission processes in Spark-Ignition (SI) engines. By means of both numerical and experimental investigations, it tries to answer some still open questions related to this complex topic. Different fuels are considered, such as gasoline and other promising cleaner alternatives for the future, including natural gas. 3-D Computational Fluid Dynamics simulation are used as useful additional tool to investigate the fuel-related soot emissions and help explain the experimental-derived results. The modified version of the KIVA-3V code, developed at the Engine Research Center (ERC) of the University of Wisconsin-Madison, is used for the present modeling work. It includes improvements in its ignition, combustion and emission models. In particular, a semi-detailed soot model and a chemical kinetic model, including Poly-Aromatic Hydrocarbon formation, are coupled with a SI model and the G equation flame propagation model for the engine simulations and for predictions of soot mass and particulate number density. The present work improves and extends the laminar flame speed correlations for several fuels of practical use in order to assure the correct prediction of combustion phasing and in-cylinder pressure evolution. The effects of a load increase achieved by pure oxygen addition in gasoline SI engines, as well as, the influence of natural gas composition on combustion are investigated. Furthermore, additional extensive experimental investigations provide more insights about the effects of lubricant oil on particle emissions from both gasoline and natural gas SI engines. In this last case both Port Fuel and Direct Injection mode are considered. The experimental tests were performed at the �Istituto Motori CNR�, Italy.