The proposed paper deals with analysis of gas exchange process and combustion in a natural gas SI ICE equipped with scavenged pre-chamber. It is achieved by 3-D CFD simulation of the whole engine cycle while using LES as a turbulence model and ECFM as a combustion model to describe turbulent flame front propagation. Due to the nature of SI ICE operation and the fact that LES was applied, multiple cycles (typically 4) were calculated to consider cycle-to-cycle variations (CCV) as well. The model was verified versus experimental data for 2 different design variants of pre-chamber while considering different operating conditions for each one. After that, the model was used to test (virtually) different design variants while the main focus was put on configuration of connecting channels between pre-chamber and main combustion chamber. Sensitivity studies were carried out to evaluate the influence of different design parameters. The comparison considered both integral parameters (e.g., ROHR) and detailed 3-D CFD data (e.g., local space distribution of fuel in pre-chamber). The main conclusions are the following: • The scavenging strategy, which is based on pure fuel being flown into pre-chamber during late exhaust stroke and intake stroke, is sufficient in terms of pushing almost all burnt gases out of pre-chamber. The local equivalence ration at spark plug is within ignitable limits. • The mixture homogeneity inside pre-chamber at point spark ignition is reasonably homogeneous, however it can be improved. There are significant variations among the cycles. • There is always optimal value of different parameters: number/size of connecting channels, their space configuration, location of spark plug, etc. • Regarding the size of pre-chamber, 2 different cases were considered. The bigger one seems to be slightly better. Its particular shape is usually limited by design constraints, which leads to relatively tall design – this makes mixing in pre-chamber more problematic and may lead to strong mixture stratification.

Dr. Oldrich Vitek, Czech Technical University in Prague, CZECH REPUBLIC Dr. Vit Dolecek, Czech Technical University in Prague, CZECH REPUBLIC Ing. Zbynek Syrovatka, Czech Technical University in Prague, CZECH REPUBLIC Dr. Jiri Vavra, Czech Technical University in Prague, CZECH REPUBLIC Prof. Michal Takats, Czech Technical University in Prague, CZECH REPUBLIC Dr. Bohumil Mares, Czech Technical University in Prague, CZECH REPUBLIC