Optimization of the GDI engine operation with stoichiometric mixtures using numerical modeling

The worldwide interest with respect to the environmental impact of energy conversion systems and the need to limit the dependence upon fossil fuels are greatly affecting the development strategies within the automotive industry. Although various alternative technologies to internal combustion engines have been considered in recent years, it is well assessed that these will continue to be the preferred and most diffused propulsion systems in transportation, at least in the near future. Various ideas are being proposed and adopted by engine manufactures and researchers to improve the performance, and especially increase the energy efficiency, of existing technologies. The work, described in this paper, focuses on the numerical and experimental study of the high performance Alfa Romeo 1750cc gasoline direct injection engine, where the mixture formation occurs in a wall guided mode. The objective is to assess computational fluid dynamics optimization procedures which may enable the determination of the optimal parameters for the highest engine power output under stoichiometric operating conditions without the occurrence of knocking. A preliminary experimental analysis is presented in order to characterize the engine considered and to investigate the phenomenon of knocking that occurs as the spark advance is increased. The collected data are employed to elaborate a predictive criterion for the knocking occurrence, as well as to validate both the one- and three-dimensional models developed for the prediction of the engine working cycle. In fact, a complete engine three-dimensional model and a three-dimensional computational fluid dynamics model limited to the closed valve operation are assessed and used in specially formulated optimization procedures. A proper design of experiment space is built case by case.