Split injection in a GDI engine for energy efficiency increase and particulate matter reduction

Euro 6 standard over the New European Driving Cycle emissions from light passenger and commercial vehicles has been implemented with effect from September 2014. The relevant EU Commission Regulation 459/2012 introduces particle number limits also for gasoline direct injection engines. Particulate matter formation indeed takes place also in this kind of propulsion system due to the inhomogeneity of the air-to-fuel ratio of the mixture and the presence of locally rich zones, or as a consequence of film deposition over walls. Present work is aimed at identifying the mechanism of particulate matter formation in a GDI engine under a slightly lean operating condition. The possibility to resort to split injection events to maintain high the combustion efficiency and simultaneously reduce this pollutant is also explored. A synergic numerical and experimental study is indeed performed to optimise the engine control strategy with respect to both the environmental and the energetic performance