Air Mass Flow Analysis for SI Engine: EGR and Scavenging

In order to lower the Nitrogen Oxides (NOx) concentration in internal combustion engine emissions and to improve performance, Exhaust Gas Recirculation (EGR) and Scavenging mechanism are introduced. EGR recirculates a fraction of the exhaust gas back into the cylinders, thus diluting the intake air. This lowers the maximum combustion temperature and, since the formation of NOx is heavily dependent on temperature, it results in a reduction of NOx concentration. Similarly, the Scavenging phenomenon is the air mass flowing from intake manifold directly to exhaust manifold, due to an overlap of intake and exhaust valves, without participating at the combustion. In this paper, the authors present a mean value engine model, aimed at the challenging purpose of the analysis of EGR and Scavenging. The model is based on an innovative approach for engine dynamics conceived mainly on the analogy with electric systems.