Optical investigations of nozzle geometrical and dynamic factors on formation and development characteristics of string cavitation with large-scale diesel tapered-hole nozzles

Abstract

Cavitation is known to be an essential physical phenomenon to induce the fuel primary breakup process, which further influences subsequent secondary atomization and combustion in diesel engines. Different from normal geometry-induced cavitation, the special vortex-induced cavitation, which may influence strongly spray characteristics, is seldom investigated comparatively. In this paper, formations and developments of string cavitation are captured in scaled-up transparent replicas of diesel tapered-hole nozzles by high-speed imaging technology. The ensemble average images were post-processed by MATLAB code for characterizing the string cavitation at fixed needle lifts. The results indicate that string cavitation tends to occur initially in the middle of the nozzle holes. Besides, shedding bubbles from geometry-induced cavitation may stimulate the string cavitation inception as an inducing factor. The morphology and duration of both two types of string cavitation are largely influenced by needle lifts and cavitation number. Moreover, it is concluded that string cavitation hardly occurs in nozzles with low hole entrance location, and the hole entrance rounding structure changes the distribution characteristics of string cavitation. Finally, it is ascertained that the variation of magnification ratio changes little or nothing about development and distribution characteristics of string cavitation.

Single and twin string cavitation swirling flows in multi-hole mini-sac diesel injector and sprays

“…It was clarified that super cavitation in a nozzle induces a large and strong turbulence, and enhances liquid jet atomization. Recently, it was pointed out that string cavitation may appear in multi-hole fuel injectors at low needle lift (Miranda et al, 2002;He et al, 2016;Wei et al, 2022), which increases spray angle (Hayashi et al, 2013;Pratama et al, 2016;Prasetya et al, 2021;Guan et al, 2021) and decreases droplet diameters (Mitroglou et al, 2011). Particle image velocimetry (PIV) analysis on a plane through the central axis of a sac of mini-sac injector was carried out to show the vortex flow in a sac (Hayashi et al, 2013;Prasetya et al, 2021).…”

Assessment of turbulence and cavitation models in prediction of vortex induced cavitating flow in fuel injector nozzles

“…The X-ray tracer imaging method was also employed in the work of Moon et al (Moon et al, 2019) that visualized the transient behavior of vortex-induced string cavitation in steel injector nozzles. However, the scale effect on string cavitation in enlarged injector nozzles is unclear (Arcoumanis et al, 2000;Guan et al, 2021a). The nuclei and micro-bubbles, cannot be scaled up in the liquid, but affect the growth and collapse of cavitation bubbles (Cao et al, 2021;Parkin, 1952).…”