Study on the Combustion Characteristics of Diesel Spray with Split Injection

To investigate the effects of split injection on the diesel combustion process during the cold-start phase of a diesel engine, the two-color imaging method was employed to study the influence of key injection parameters on flame temperature and soot concentration under cold start conditions. Compared with single injection, the average flame temperature and integrated KL factor during split spray combustion increased significantly, with the average peak combustion temperature rising by approximately 300 K and the integrated KL factor increasing by up to around 4×10⁴. As the pilot injection ratio increased and the injection dwell decreased, the average flame temperature and integrated KL factor initially increased and then decreased, reaching their maxima at a pilot injection ratio of 30% and an injection dwell of 900 μs, respectively. For split injection parameters, the elevated temperature in the interaction zone shortened the flame lift-off length, resulting in an inverse relationship between local mixing rate and combustion enhancement. Although enhanced soot oxidation and improved local mixing contributed to suppressing soot formation, the macroscopic evolution of soot remained unchanged with variations in injection parameters. Under cold start conditions, the integrated KL factor exhibited a trend consistent with the total integrated natural luminosity, indicating that the combustion enhancement effects induced by injection parameter variations were the primary factors influencing the macroscopic evolution of soot.