Analysis of Flow and Cavitation Phenomena in Diesel Injection Nozzles and Its Effects on Spray and Mixture Formation

In modern DI Diesel engines the raw emissions of NOx and soot are affected, apart from the fuel injection rate, by atomization of the liquid jet and mixing of the fuel with the combustion air. Thereby details of the fuel flow inside the injection nozzle play an essential role. In order to determine the general mechanisms and the effect of individual nozzle configuration parameters on the fuel atomization and the fuel spray propagation, methods for optical diagnostics and CFD have been developed at the DaimlerChrysler Research. These methods are combined with an analysis of the injection system hydraulics and linked to a detailed analysis of mixture formation and combustion inside an optically accessible engine. The first part of the paper methods for the experimental investigation with transparent 1- and 6- hole nozzles in real size geometries under high pressure conditions are described. Special emphasis is put on CFD methods for modeling the cavitating two phase nozzle flow. In the second part the processes occurring in a sac hole nozzle of a common rail injector during the complete injection event are discussed. The influences of the spray hole position, inlet rounding and conical shape of the spray hole are presented. Finally a comparison between a needle lift controlled (CR = common rail) and a pressure controlled (PLN = pump line nozzle) injection system is made.