CFD Modeling of Gas Exchange, Fuel-Air Mixing and Combustion in Gasoline Direct-Injection Engines 2019-24-0095
Gasoline, direct injection engines represent one of the most widely adopted powertrains for passenger cars. However, further development efforts are necessary to meet the future fuel consumption and emission standards imposing an efficiency increase and a reduction of particulate matter emissions. Within this context, computational fluid dynamics is nowadays a consolidated tool to support engine design and development and this work is focused on the development of a set of CFD models for the prediction of combustion and soot formation in modern GDI engines. The one-equation Weller model coupled with a zero-dimensional approach to handle initial flame kernel growth was applied to predict flame propagation. Soot formation was described with a semi-empirical, two-equation model accounting for the most important steps such as nucleation, surface growth, coagulation and oxidation. To account for mixture fraction fluctuations, burned gas chemical composition is computed using tabulated kinetics with a presumed probability density function. Assessment of the combustion model was done with experimental data of flame radius evolution at different operating conditions. Afterwards, simulations were carried out for a turbocharged gasoline, direct-injection engine with variable valve actuation. Different operating points were considered including variation of speed and load: a detailed comparison is performed between computed and experimental data of in-cylinder pressure, heat release rate and soot emissions.