An Experimental Investigation of Combustion and Soot Formation of Sprays from Cluster Nozzles for DI Diesel Engines

One of the basic topics in the design of new injection systems for DI Diesel engines is to decrease the soot emissions. A promising approach to minimize soot production are nozzles with clustered holes.

A basic idea of the Cluster Configuration (CC) nozzles is to prevent a fuel rich area in the center of the flame where most of the soot is produced, and to minimize the overall soot formation in this way. For this purpose each hole of a standard nozzle is replaced by two smaller holes. The diameter of the smaller holes is chosen so that the flow rate of all nozzles should be equal. The basic strategy of the cluster nozzles is to provide a better primary break up and therefore a better mixture formation caused by the smaller nozzle holes, but a comparable penetration length of the vapor phase due to merging of the sprays. Three possible arrangements of the clustered holes are investigated in this study. Both the cluster angle and the orientation to the injector axis are varied. The common rail Diesel injector is installed in a combustion vessel, in order to provide nearly quiescent high-pressure and high-temperature conditions. As fuel, Diesel and n-decane, which is a commonly used model fuel for standard Diesel fuel, are used.

The combustion and soot formation are analyzed using three different measurement techniques. The hot reaction zone is visualized using OH* chemiluminescence imaging which occurs during the second stage ignition. The local soot concentration during combustion is measured semi-quantitatively using Laser Induced Incandescence (LII). In both measurements the soot luminosity is recorded simultaneously using a second camera or a double frame camera, respectively. The soot formation is discussed for all nozzles. The data indicates that soot formation can be reduced using cluster nozzles under these conditions.