6. Investigation of Influence of Injection Pressure on Gasoline Fuel Spray Characteristics Using Numerical Simulation

Maximum fuel injection pressure in gasoline direct injection engine is expected to increase because of its potential to reduce emissions while maintaining a high efficiency in spark ignition engine. Present gasoline injectors in the market operates in the range of 20–30 MPa. Because of many positive effects of high injection pressure for the emission reduction and fuel efficiency, an interest has been developed to investigate the spray behavior at around 40 MPa, 60 MPa and even more higher injection pressure. A fundamental investigation of spray characteristics at high-pressure injection will help to develop the understanding of spray behavior at such elevated pressure. In the present study, a gasoline fuel spray was studied through the numerical model at an injection pressure ranging from 40 to 150 MPa. A numerical simulation was performed in an optical accessible constant volume chamber. The chamber was effectively non-reacting and non-vaporizing condition since the focus was on the spray droplets. In the numerical model, gas flow was calculated by large-eddy simulation (LES) method and the liquid phase was accounted by a standard Lagrangian spray model. The fuel spray atomization was modelled using the Kelvin Helmholtz—Rayleigh Taylor (KH-RT) model, and droplet size distribution followed the Rosin-Rammler distribution function. Simulation results were validated by comparing the liquid penetration length of spray with the experimental data at different fuel injection pressures. Then, the mean droplet sizes such as arithmetic mean diameter and Sauter mean diameter of the spray droplets were compared with the measure droplet sizes as a function of pressure. The spray droplet size distribution was also shown along with measured droplet sizes. The result shows that the liquid length penetration of the spray was significantly increases together with the higher probability of smaller droplet by increasing the fuel injection pressure. Moreover, the mean droplet sizes were also reducing by increasing the fuel injection pressure, such as the droplet SMD was reduced from 13.5 to 7.5 \( \upmu \)m by injecting the fuel at pressure 150 MPa instead of 40 MPa.