Optimal selection of the combustion mode in a turbo-charged diesel engine for reduced fuel consumption, noxious emissions and radiated noise

Present work focuses on the development of a numerical method for the optimization of the combustion process of a six-cylinder diesel engine equipped with a high pressure injection system and a variable geometry turbocharger. A preliminary experimental analysis is carried out to characterize the considered engine under various speeds and loads. The collected data are employed to tune proper numerical 1D and 3D models, able to reproduce the engine behaviour in terms of performances (in-cylinder pressure, air-flow rate, fuel consumption), noxious emissions (soot, NOx) and radiated noise. In particular, a 1D tool is developed with the aim of characterizing the flow in the intake and exhaust systems and predicting the engine-turbocharger matching conditions (through a shortroute EGR circuit); a 3D model is assessed to reproduce into detail the in-cylinder thermofluidynamic processes, including mixture formation, combustion, and main pollutants production; a in-house routine is finally written for the prediction of the combustion noise. Obviously data exchange between codes is previewed. The 1D, 3D and combustion noise models are checked with reference to the experimentally analyzed operating points. The formulation is finalised to their inclusion within an external optimizer (ModeFrontier), enabling the optimal selection of the combustion controlling parameters to improve the engine performances and to contemporary minimize noise, emissions and fuel consumption. Under the hypothesis of a pilot-main injection strategy, a multiobjective optimization problem is solved through the employment of a genetic algorithm. It is shown that the engine has to work under different combustion modes (low temperature combustion, partially premixed combustion, homogeneous charge compression ignition) depending on the importance given to the various