Diesel Spray Modeling Under Off-Axis Needle Displacement 2015-01-0922
Relatively recent investigations, basing on experiments as well as on modeling, have highlighted that the needle displacement in common-rail diesel injectors is affected by radial components. The effects of such “off-axis” needle displacement on fuel flow features have been so far investigated within the nozzle, only.
The objective of this work is to extend the attention towards the formation of fuel sprays, when needle off-axis condition is encountered. In such a viewpoint, the development of each fuel spray has been modeled taking into account the hole-to-hole variations induced by the needle misalignment.
The investigation has been carried out basing on 3D-CFD campaigns, in AVL FIRE environment. The modeling of diesel nozzle flow has been interfaced to the spray simulation, initializing the break-up model on the basis of the transient flow conditions (fuel velocity, turbulence and vapor fraction) at each hole outlet section.
The current investigation has been performed on a complete geometry of a common rail multi-hole VCO nozzle. Simulations have shown how the needle misalignment is reflected in the formation of the fuel jets. Quantitative results have been provided on each fuel spray development, pointing out the hole-to-hole variations induced by the needle off-axis displacement.