Effect of injection strategy on the spray development process in a single-cylinder optical GDI engine

The present study deals with the spray development and atomization with a wide range of injection pressure and injection timing in a Gasoline Direct Injection (GDI) system. A wide range of injection pressure was swiped from 5 MPa to 30 MPa to investigate the effect of injection pressure on spray behaviors. The macroscopic spray images taken by a high-speed camera were used to investigate the influence of the injection pressure on the spray development process. Spray tip penetration, cone angle, and spray tip velocity were measured from the spray images, and the breakup regimes were predicted using dimensional analysis. Experimental results showed that an increase in injection pressure caused a decrease in droplet size based on the sequential spray images and breakup regimes. However, for injection pressures over 20 MPa, the effect of injection pressure on spray characteristics was minimal with the injection pressure increase. Meanwhile, the spray images in the GDI engine revealed that injection timing was directly related to the air-fuel mixture homogeneity. Strong intake flow broke up the spray structure and mixed the fuel with the air effectively. This study proposes a proper injection pressure range for GDI injection systems, and the results in the present study would be helpful in comprehending gasoline spray characteristics.