3D-CFD Methodologies for a Fast and Reliable Design of Ultra-Lean SI Engines

The continuous pursuit of higher combustion efficiencies, as well as the possible usage of synthetic fuels with different properties than fossil-ones, require reliable and low-cost numerical approaches to support and speed-up engines industrial design. In this context, SI engines operated with homogeneous ultra-lean mixtures both characterized by a classical ignition configuration or equipped with an active prechamber represent the most promising solutions. In this work, for the classical ignition arrangement, a 3DCFD strategy to model the impact of the ignition system type on the CCV is developed using the RANS approach for turbulence modelling. The spark-discharge is modelled through a set of Lagrangian particles, whose velocity is modified with a zero-divergence perturbation at each discharge event, then evolved according to the Simplified Langevin Model (SLM) to simulate stochastic interactions with the surrounding gas flow. For the active prechamber configuration, instead, a CFD methodology based on a 3DRANS approach is proposed to model the combustion process, in which the air-fuel mixture distribution inside the prechamber is properly considered without a 3D simulation of the main chamber intake process. This is carried out through a non-reacting simulation of the prechamber-only until IVC, then results are interpolated on a different 3D engine mesh for the further compression and combustion stages. The proposed methodologies were assessed and validated against experimental measurements at different operating conditions.