Research on the effects of split injection on diesel engine spray impingement and fuel film under cold-start conditions

In high-intensity diesel engines, substantial fuel is injected onto the piston wall, which can readily produce pool fire and carbon soot during subsequent combustion. The split injection strategy effectively mitigates the wall impingement phenomenon. Employing a constant volume combustion chamber (CVCC) to emulate the diesel engine cylinder's environment during a cold start, this study experimentally investigates the shape characteristics of diesel wall impingement and the evaporation behavior of fuel film under split injection using the refractive index matching method (RIM) and backlit technique. Results indicate that the spray area resulting from split injection is less extensive than that from a single injection. Moreover, the volume and area of the fuel film created by split injection impingement are less than those from a single injection event. The volume and area of the resulting fuel film are inversely proportional to the ratio of first injection. The injection dwell times between 0.7 ms and 1.5 ms demonstrate that longer dwell times correspond to smaller fuel film volumes and areas. Conversely, shorter injection dwell times of 0.3 ms and 0.5 ms lead to a minor reduction in the volume and area of the fuel film, attributed to the presence of the first injection film. After a period of evaporation, fuel films resulting from a single injection and split injections with a small injection ratio and dwell time still retain a significant thickness.