Real-size Real-shape Real-pressure transparent nozzles to contribute to nozzle design and cavitation control for GDI
Antonio Agresta  1@  , Jerome Helie  2, *@  , Eberhard Kull  3@  , Nicolas Lamarque  2@  , Anatoliy Lyubar  4@  , Stefan Schuster  4@  
1 : CPT Italy Srl
Via Vecchia Livornese, 1319 - 56122 San Piero a Grado (PI) -  Italy
2 : CPT France SAS
CPT France SAS
1 avenue Paul Ourliac, 31100 Toulouse -  France
3 : CPT Group GmbH
Regensburg -  Germany
4 : CPT Germany
Regensburg -  Germany
* : Corresponding author

Transparent nozzles are used for years to allow optical measurements of cavitating flow in order to avoid erosion and to master the effect on the atomization. Until now, geometry variation with transparent nozzles were typical used mostly in simplified conditions having a 2D flow field.

2D holes where initially considered and are still useful for model validation. The hole inlet radius was identified to greatly influence the cavitation inception. The development of the cavitation length increases with the pressure difference, and lastly, the role of the cavitation collapse for the specific conditions of a collapse close to the vicinity of the hole exit was identified to improve the atomization. Central holes are cavitating uniformly and lead to flow conditions which cause hydraulic flip, therefore asymmetric inlet conditions and inclined holes were studied. Unsteady shear cavitation process was found. As cavitation cannot be scaled up to represent correctly the nucleation and bubbles – pockets transitions, the realization of real size nozzle was a great progress toward more representative transparent nozzle when compared to real parts.

A proof of concept of a real-size, real-shape, real-pressure, representative surface roughness, transparent nozzles is demonstrated in the present paper. This kind of nozzle can be used for easy geometry variation or Design Of Experiment. The nozzle is mounted on an actuated valve. It contains an angular portion of a real nozzle, including the needle-body area, the sac geometry, the hole geometry and the external nozzle shape. The working fluid can be chosen as representative as a real fuel, and for simplicity N-heptane is chosen here. It is shown that the maximum tensile stress can be reduced with reworking the main constrained area. Wide view pictures return the penetration curve and close-up visualizations with a Laser – pulse of 10ns are realized in liquid-into-liquid configuration as compared to liquid-into-air are proposed. Shear and string cavitation are observed.

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