Split injection flash boiling spray for high efficiency and low emissions in a GDI engine under lean combustion condition

Abstract

Homogenous, lean combustion has been considered a feasible approach to further improve the performance of the state-of-the-art gasoline direct injection (GDI) engines. However, notable challenges have been seen in properly controlling the lean combustion for satisfactory fuel efficiency and emission performance. To achieve a more homogenous fuel-air mixture for the lean combustion, this manuscript investigated the application of flash boiling atomization in an optical accessible, single cylinder engine operated under lean combustion conditions. Both single injection and split injection schemes were tested and the performance of the engine was evaluated by both traditional and non-intrusive approaches. Imaging methods including micro-LIF-PIV, Mie scattering, and flame chemiluminescence were used to interpret the combustion characteristics inside the engine cylinder. It was found that flash boiling has improved the combustion efficiency, and also PN emission performance if the split injection was used. Spray analysis also indicates that the reason for such phenomena is that fuel-air mixing under flash boiling condition is more complete, thus results in a notably faster flame speed and increased indicative mean effective pressure (IMEP).