Microscopic and macroscopic analysis of the flashing and non-flashing ethanol blended fuel for the direct injection sprays

Gasoline direct injection (GDI) engines offer improved fuel atomization, performance, and reduced emissions. Flash boiling in GDI engines enhances atomization. This study investigates ethanol-gasoline blended fuel spray using a single-hole direct atomizer. Micro- and macroscopic experimental analysis was conducted using a Galilean beam expander and Nd: YAG laser. The current study focused on initial, quasi-steady, and post-injection stages of flashing and non-flashing sprays. The transitional flashing jet exhibited various shapes similar to nonflashing sprays. An orbicular-shaped jet was observed during flare flashing at 0.03 MPa chamber pressure and 363 K fuel temperature. It exhibits rapid axial momentum, resulting in a Reynolds number of 8.0 x 104, 1.3 and 2.15 times higher than the transitional and non-flashing sprays. Additionally, it has an estimated nucleation rate of 3.22 x 10-2 m-3s-1 using classical nucleation theory, which is 10 times higher than the transitional flashing, leading to improved atomization. However, spray collapse was observed under flare flashing with reduced chamber pressure, attributed to local condensation and subsequent pressure drop in spray core. Under flare flashing at a fuel temperature of 403 K, the Ohnesorge number is 2.95 x 10-3, which is 0.8 times and 0.7 times lower than the fuel at 383 K and 363 K, respectively. The nucleation rate for flare flashing increases with higher fuel temperature, leading to improved atomization and a reduced likelihood of spray collapse. Post-injection spray structures in the near-nozzle show a transition from coarse to fine and dilute to densely populated, with changes in degree of superheating.