Modeling flash boiling breakup phenomena of fuel spray from multi-hole type direct-injection spark-ignition injector for various fuel components

A flash breakup model was developed in this study, based on bubble dynamics. The Rayleigh-Plesset equation was used to predict bubble growth inside of a droplet. A single bubble for each droplet was assumed. When the void fraction exceeds critical value, breakup was assumed. The velocity component normal to the direction in which the droplet moved was predicted by the sum of the velocities predicted by energy conservation, the pressure difference between the inside and outside of droplet, and the bubble growth rate. The thermodynamic-mechanical breakup model was formed using the flash breakup and Kelvin-Helmholtz Rayleigh-Taylor breakup models. Using the developed breakup module, the decrease in spray tip penetration, spray plume expansion, and change in spray target were predicted for single-component fuels and compared with experimental results. A gasoline flash boiling spray was modeled using various fuel vapor pressure for the Rayleigh-Plesset equation. From the comparison between the analyses with and without the flash breakup model, it was concluded that the flash breakup model should be used to predict deformations in spray structure for flash boiling sprays.