Investigation of Diesel Spray Primary Break-up and Development for Different Nozzle Geometries 2002-01-2775

The nozzle configuration for an injector is known to have an important effect on the fuel atomization. A comprehensive experimental and numerical investigation has been performed to determine the influence of various internal geometries on the primary spray breakup and development using the electronically controlled high-pressure diesel injection systems.

Different types of multi-hole minisac and VCO nozzles with cylindrical and tapered geometries, and different types of single-hole nozzles with defined grades of Hydro Grinding (HG) were investigated.

The global characteristics of the spray, including spray angle, spray tip penetration and spray pattern were measured from the spray images with a high-speed drum camera. A long-distance microscope with a pulsed-laser as the optical shutter was used to magnify the diesel spray at the nozzle hole vicinity. A CFD analysis of the internal flow through various nozzle geometries has been carried out with a commercial code. The CFD analysis includes a numerical model simulating pressure distribution, kinetic turbulent energy distribution, velocity distribution, and the effect of cavitation.

The visualization and simulation results provide The visualization and simulation results provide dynamic information about the spray structure. The near field spray observation is shown to strongly depend on the nozzle internal geometry and primary spray breakup. The CFD analysis verifies this. The simulation of the internal flow shows that internal geometry has dramatic effects on exit flow and the subsequent primary spray breakup. Comparison of cylindrical and tapered geometry nozzles shows that spray hole geometry influences the internal flow. Consequently, the internal flow such as pressure distribution, kinetic turbulence energy, velocity profile, and cavitation influences injection-rate and degree of atomization. Investigations of the spray break up close to the nozzle exit have shown that there are significant differences in the spray structure for single-hole versus multi-hole nozzles.