Experimental study on the combustion and soot emission of twin-spray collision at various collision angles and injection pressures under marine engine’s conditions

In a large-bore marine engine, the larger cylinder diameter and space correspond to more fuel injection in a limited time of each working cycle. The fuel injection of multiple injectors can achieve fast atomization and homogeneous fuel-gas mixing performance, which is liable to cause the spray collision problem, but the twin-spray collision phenomenon is rarely observed and studied. Therefore, this work aims to explore the effect of various collision angles (60°, 90°, 120°, and 150°) and injection pressures (60, 100, 140, and 180 MPa) on the combustion and soot emission of twin-spray collision process. Based on a large-bore constant volume chamber and two optical diagnostic techniques, the ignition delay time, initial ignition location, flame collision structure, and soot emission luminosity are obtained in a reactive atmosphere. The results show that near the collision point, there exists a fan-shaped flame structure. Due to the mutual entrainment from twin sprays, the ignition delay time of twin-spray collision is shorter than that of single free spray. As a result, at the constant diesel injection mass, the soot emission intensity of twin-spray collision becomes higher. With the collision angle increasing, the ignition delay time becomes shorter, and the initial ignition location gradually moves upstream, while the soot emission intensity becomes higher. The time integrated natural luminosity difference between 60 and 180 MPa gradually decreases and then reverses. Moreover, the wider collision angle also makes the ignition delay time less sensitive to the injection pressure.