Investigation of diesel injector nozzle flow number impact on spray formation and combustion evolution by optical diagnostics

The present paper describes an experimental investigation over the impact of diesel injector nozzle flow number on spray formation and combustion evolution for a modernEURO5 light-duty diesel engine. The analysis has beencarried out by coupling the investigations in non evaporativespray bomb to tests in optical single cylinder engine in firingconditions.The research activity, which is the result of a collaborativeproject between Istituto Motori Napoli - CNR and GMPowertrain Europe, is devoted to understanding the basicoperating behaviour of low flow number nozzles which areshowing promising improvements in diesel engine behaviourat partial load. In fact, because of the compelling need topush further emission, efficiency, combustion noise andpower density capabilities of the last-generation dieselengines, the combination of high injection pressure fuelpumps and low flow number nozzles is general trend amongmajor OEMs. Therefore, aim of this paper is to provide adeeper understanding about the link between the nozzle flownumber, the spray and mixture formation and the consequentcombustion behaviour for different nozzle geometries andengine operating conditions typical of diesel engineoperating. Main deliverables of the above mentioned activitywill be guidelines for a balanced nozzle flow numberselection and references for upgrading 3D-CFD simulationsspray models.Spatial and temporal spray characterizations have beenevaluated for three different nozzle flow numbers for a 2.0Ldiesel engine in various operating conditions. The resultsconfirm that by reducing the flow number, for low injectedquantities typical of low load and speed engine conditions,better fuel/air mixing is achieved. On the contrary, increasingthe injected quantity (as for medium/high load and speedconditions) flow number reduction requires engine recalibrationin order to keep the advantages of mixtureformation.