CFD simulations were conducted to investigate the combustion process in a high performance DI gasoline engine. The Extended Coherent Flame combustion Model (ECFM), implemented in the STAR-CD code, was used. This model is based on a flame surface density transport equation that can describe inhomogeneous turbulent premixed combustion.
The injection phase was simulated using a Lagrangian modelling approach. The correlation of key spray characteristics, like jet penetration and Sauter mean diameter, with experimental measurements is presented.
The numerical analysis also focused on cylinder charge motion and mixture formation. It was found that these processes have a major influence on combustion performance. CFD combustion simulations for homogeneous and heterogeneous mixtures gave an insight into the performance improvement theoretically achievable by improving mixture preparation.
Two engine points representative of part load and full load conditions were analysed for different engine configurations. The CFD results were compared directly against engine test data and good agreement was found for cylinder pressure and fuel burn rate.
After analysis of the results, it was clear which of the designs was optimised for combustion performance.