Flash boiling atomization is considered a potential solution to multiple issues encountered in fuel atomization for internal combustion engine applications. It has been demonstrated that flash boiling combustion can reduce soot emission under cold-start conditions, while the analysis was still preliminary and limited to engine cold-start conditions. This work investigates the performance of flash boiling combustion in comparison to sub-cooled spray combustions realized with the variation of injection timing. An optical engine facility was used to capture the combustion characteristics with a high-speed color camera, with the temperature of the engine coolant maintained at 60 °C. HSV color model and modified digital CH*/C2* ratio (excess air intensity) to study different flame regions and local combustion richness in the optical engine. The results show that under the conditions tested, flash boiling can improve the efficiency of the engine while reducing the PN emission simultaneously. Furthermore, it was seen that flash boiling combustion could yield a faster flame speed, uniform distribution of flames and less rich mixtures. Finally, color model analysis for transient and averaged flame images is also in good agreement with actual engine performance.
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