Numerical Modelling and Optimization of the Mixture Formation Processby Multi-Hole Injectors in a GDI Engine

Abstract

The problem of the environmental impact of energy conversion systems is particularly felt in the automotive field as a consequence of the wide diffusion of internal combustion engines within the transportation systems, and of the very high concentration of vehicles in the urban areas. Several actions, therefore, are today being taken by car manufacturers and researchers towards the development of more and more efficient propulsion systems, characterised by lower and lower pollutants emissions. In fact, despite the recent efforts aimed at developing alternative technologies, it is likely that the internal combustion engine will remain dominant for the next 30 years and beyond. This implies that the study and the optimisation of the thermo-fluid-dynamic processes characterising its operation will undoubtedly continue to play a determining role in the forthcoming scenario. The major difficulties today encountered in the experimental characterization of combustion and pollutants formation in both spark ignition (SI) and compression ignition (CI) engines rely in the low spatial and temporal resolution achievable from measurements, as well as in the possible influence of instruments on the same phenomena to be investigated. The diagnostics capability surely benefits of the development of non-intrusive optical techniques, although constructive and economic problems still hinder their broad use. On the other hand, the introduction of increasingly accurate physical and chemical models and the simultaneous growth of the processors speed have led to a diffuse use of computational fluid dynamics (CFD) techniques, especially in the phase of engine design. A wide variety of geometrical configurations or sets of engine parameters, indeed, are today suitable of being analysed into detail through models of various complexities at relatively low costs, or optimised according to predefined objectives. As regards SI engines, in particular, the most pursued solution for the improvement of fuel economy relies on engine downsizing, coupled with turbo-charging and direct injection (DI): the engine displacement is reduced, whereas an increase of the low end torque is realised by air boosting, compression ratio rising and gasoline injection directly in the combustion chamber. These measures allow overwhelming the main shortcoming of engines mounting port fuel injection (PFI) systems, with mixture formation occurring within the intake ducts, namely the significant engine pumping losses at part-load operation (where the engine works during most of an urban driving cycle), caused by the throttle load