ADVANCED NUMERICAL APPROACH TO SIMULATE GDI SPRAYS UNDER ENGINE-LIKE CONDITIONS

Gasoline direct-injection (GDI) engines provide both higher engine power and better fuel efficiency than port-injection gasoline engines. However, they emit more particulate matter (PM) than the latter engines. Fuel stuck on walls of pistons and combustion chambers forms a high-density region of fuel in the air/fuel mixture, which becomes a source of PM. To decrease the amount of PM, fuel injectors with short length of spray-penetration are required. A fuel-spray simulation was previously developed; that is, the air/fuel-mixture simulation was integrated with the liquid-column-breakup simulation. The developed fuel-spray simulation was used to optimize the nozzle shapes of fuel injectors for gasoline direct-injection engines. In the present study, the factors that influence spray-penetration length were identified by the numerical simulation. The simulation results were validated by comparing the simulated spray-penetration length with the measured ones and revealing good agreement between them. Angle alpha was defined as that formed between the direction of flow entering the nozzle inlet and the direction of flow leaving the nozzle outlet; in other words, a indicates a change of flow direction. It was found that alpha and spray-penetration length was closely related. Velocity that are accelerated with alpha were studied, and it was found that the velocity within a plane perpendicular to the center axis of the nozzle increases with increasing alpha.