Modified bowl geometry for cluster nozzles in direct-injection diesel engines

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 conditions because the spray penetration becomes exceedingly inadequate. For this reason, the cluster concept was chosen as the means to realize lean combustion. To make the use of clusters in a diesel engine feasible, a significant redesign of the typical in-cylinder geometry would probably be required to promote efficient air utilization. The new combustion chamber was designed with a smaller diameter and deeper bowl. It is expected to improve fuel—air mixing by better spray guidance. The study identifies the aspects of combustion and pollution formation that are affected by mixing processes and offers guidance for better matching of the piston geometry with the spray plume geometry for enhanced mixing. Various clusters were investigated to achieve variation in the injection timing for different test points in the original piston bowl chamber and the new bowl chamber, and the results are compared with those for a conventional nozzle. The cluster with the best results for smoke emissions in the first set of tests was also tested for different swirl ratios and different nozzle protrusion lengths.