Optimizing the injection pressure for cluster nozzle concepts in a direct injection diesel engine

Abstract

A combination of high-pressure injection and small orifices will be one of the strategies to achieve lean combustion. However, equispaced small orifices tend to increase soot under high-load condition because the spray tip penetration becomes exceedingly inadequate. For this reason, the cluster concept was chosen as a means to realize lean combustion. Six clusters were investigated with different injection pressures under part-load condition and high-load condition in a single-cylinder diesel engine, and the results were compared with a reference nozzle. The clusters tend to produce higher smoke than the reference nozzle for low injection pressures under conventional injection timing because the spray from the clusters with a shorter spray tip penetration loses momentum near the piston bowl. However, the clusters show improved smoke emissions with higher injection pressures. The combination of high-pressure injection and cluster concepts can be seen as one of the solutions to achieve lean combustion for diesel engines. Clusters with high-pressure injection have improved emissions, as better fuel atomization and evaporation are achieved while holding momentum near the piston bowl and maintaining the penetration of the spray.