Investigation of flash boiling injection schemes in lean-burn gasoline direct injection engines

Flash boiling atomization has the potential to enable superior spray atomization and more homogenous fuel-air mixing. These capabilities have been demonstrated in practical combustors such as gasoline direct-injection (GDI) engines. However, optimal injection schemes for flash boiling atomization has not been thoroughly investigated yet in the existing literature. In this work, we examined such contents in the aspects of split injection schemes coupled with flash boiling atomization. The impacts were examined firstly by velocity field analysis on single injection flash boiling plumes using particle imaging velocimetry (PIV). Furthermore, an optical reciprocating engine facility was used to study flame characteristics. Spray morphologies in the cylinder were studied, and the velocity field was visualized by the optical flow method. Important combustion characteristics, such as the flame speed and combustion duration, were investigated. Finally, the thermal efficiency under different injection schemes, as well as combustion emissions were quantified and compared to discuss the influence of flash boiling atomization on lean-operated GDI engines.