Study of evaporative diesel spray interaction in multiple injections using optical diagnostics

Internal combustion engines have witnessed an ever increasing stringency in emission limits and fuel economy regulations that has continuously provoked researchers to develop complex strategies that enables engines to cope with these standards. Optical techniques have been a viable method in the study of thermal processes occurring inside internal combustion engines and provides researchers with a solid understanding of the heat and mass transfer taking place. In particular, the current study utilizes two optical techniques, diffused back illumination and schlieren imaging, to visualize the spray behavior in multiple injection strategies of evaporative diesel sprays. A novel method has been developed in order to couple the two optical techniques to visualize both liquid and vapor phases of either pilot-main and main-post injections. The influence of the auxiliary injections on the main, and vice versa, in terms of spray segmentation and spray development has been studied for two different pilot/post quantities and four hydraulic dwell times under two different chamber conditions. The spray development displayed no effect of pilot quantity and dwell time on the liquid length of the second injection. On the other hand, a more pronoun effect on the vapor phase penetration and spreading angle was evidenced by the pilot injection where the main injection has penetrated farther with a higher spreading angle as compared to the case with a single injection event. The understanding of multiple injection is thus fundamental for the improvement of thermal processes in Internal Combustion Engines.