4.2 In-cylinder simulations
Combustion analyses are developed in the framework of Star-CD 4.20, licensed by CD-adapco. The combustion model adopted for the analyses is the ECFM-3Z, whose well-known suitability for premixed as well as diffusive and autoigniting combustion regimes is a fundamental requirement for the present study. In particular, knock is taken into account thanks to the previously described hybrid user-coded/standard formulation. The fuel is injected by means of a 7-hole injector placed between the intake valves. The lagrangian phase is modelled by means of a user coded routine for primary breakup, the Reitz model for secondary break-up and the Bai-Gosman approach for droplet-wall interaction, for both fuel and water. In order to achieve a converged solution, several preliminary RANS cycles are performed based on periodic boundary conditions from a 1-D model of the whole engine provided by the engine manufacturer. Once a cyclic-converged cycle is obtained, this represents the baseline for the subsequent analyses