radial expansion of liquid jet and the air drag force are important
factors for the mushroom-shaped jet formation [4,5]. Some fuel
of the previous injection is left in the sac and this residue fuel is
reported to influence the mushroom shaped head for the next
injection [5]. For the quasi-stationary phase, the primary breakup
highly depends on the flow regimes in the injector, namely, the
injection conditions. Akira et al. [6] reported that the strong turbulence
and cavitation considerably affect the initial breakup of the
spray jet. Desantes [7] investigated the impact of cavitation on
the primary breakup by injecting fuel into a liquid of the same
type, allowing the visualization of air bubbles induced by cavitation.
The results showed that higher pressure drop led to stronger
cavitation and more air bubbles, resulting in great increase of the
microscopic cone angle.
The initial disintegration of spray is significantly affected by the
nozzle geometry [8–12]. Schugger [3] studied the effects of injector
geometry by employing PIV and High-Speed Cinematography. It
was reported that for nozzles with sharp inlet edge, stronger turbulence
and cavitation significantly boost the primary breakup.
This is because the redirection of fuel at the hole inlet is more obvious
for sharp inlet edge injector than for that with round edge.
Heimgartner et al. [13] also investigated the impact of nozzle
geometry by employing the Mie scattering technique and long distance
microscope. It was shown that the rise of injection pressure
caused an increased microscopic spray cone angle for valve covered
orifice (VCO) nozzles but the reduced cone angle for mini
sac nozzles.