EVALUATION OF WATER AND EGR EFFECTS ON COMBUSTION CHARACTERISTICS OF GDI ENGINES USING A CHEMICAL KINETICS APPROACH

The modern spark ignition engines, due to the introduced strategies for limiting the consumption without reducing the power, are sensitive to both the detonation and the increase of the inlet turbine temperature. In order to reduce the risk of detonation, the use of dilution with the products of combustion (EGR) is an established practice that has recently improved with the use of water vapor obtained via direct or indirect injection. The application and optimization of these strategies cannot ignore the knowledge of physical quantities characterizing the combustion such as the laminar flame speed and the ignition delay, both are intrinsic property of the fuel and are function of the mixture composition (mixture fraction and dilution) and of its thermodynamic conditions. The experimental measurements of the laminar flame speed and the ignition delay available in literature, rarely report the effects of dilution by EGR or water vapor. To overcome the limitations of the experimentation is possible to predict the value of the ignition delay using numerical models based on chemical kinetics theory. The increased performance of computing systems makes possible the use of mechanism with a high number of species and reactions without an excessive temporal cost. In this work a methodology, based on a non-reduced kinetic scheme and an open-source solver (Cantera), is applied to the determination of the laminar flame speed and the ignition delay for a commercial gasoline surrogate, under the typical conditions of GDI engines with the addition of the effects of dilution with water and EGR.