The authors discuss in this paper the combined effect of the exhaust recirculation rates and of the fuel injection laws on the performance and emission levels of a Common Rail diesel engine. As well known, such objectives often exhibit, conflicting trends specially when the NOx reduction is pursued through the EGR concept; on the other hand, the adoption of this method represents a preliminary tool for proceeding towards the ultimate HCCI goal. The study is carried out on a CFD basis, with an engine numerical simulation that includes the gas exchange periods and it aims at a comprehensive analysis of both the combustion development and the pollutant formation under different conditions induced by different choices of the above operating parameters. The most interesting results refer to the possibility of finding an effective compromise between the pollutant reduction and the engine performance preservation, through a proper combined choice of the EGR level and the injection timing.

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