Investigations of Split Injection Strategies for the Improvement of Combustion and Soot Emissions Characteristics Based On the Two-Color Method in a Heavy-Duty Diesel Engine 2013-01-2523

Premixed charge compression ignition (PCCI) is a new combustion mode to reduce NO_X and soot emission. It requires the optimization of the injection timing and pressure, fuel mass in pilot injection and EGR rate. A 6-cylinder, turbocharged, common rail heavy-duty diesel engine was used in this study. The effect of multiple injection strategies on diesel fuel combustion process, heat release rate, emission and economy of diesel engine is studied. The multiple injection strategies include different EGR level, pilot injection timing, pilot injection mass and post injection timing to achieve the homogeneous compression ignition and lower temperature combustion of diesel engine. Based on endoscope technology, the two-color method was applied to take the flame images in the engine cylinder and obtain soot concentration distribution, to understand the PCCI combustion in diesel engines. The results demonstrate that when EGR level is increased, the intensity of the premixed combustion becomes lower, and the ignition timing of the main combustion process is delayed. With increased EGR, the NO_X emission is decreased significantly, but soot, HC and CO emissions are increased. With the advance of pilot injection timing, the peak in-cylinder pressure becomes lower, the ignition delay of the main combustion is shortened, the NO_X and soot emissions are reduced, but the HC and CO emissions are increased. With the increase of pilot injection fuel mass, the heat release rate of the pilot injection combustion and the maximum rate of pressure rise increase, NO_X and HC emissions are higher, and PM and CO emissions are reduced. The pilot combustion flame is non-luminous. Retarding the post injection timing results in negligible change in the cylinder pressure and peak rate of main heat release, but reduction in NO_X emission, and the soot emission firstly increased and then decreased.