Modeling Atomization and Vaporization Processes of Flash-Boiling Spray

Flash-boiling occurs when a fuel is injected to a combustion chamber where the ambient pressure is lower than the saturation pressure of the fuel. It has been known that flashing is a favorable mechanism for atomizing liquid fuels. On the other hand, alternative fuels, such as gaseous fuels and oxygenated fuels, are used to achieve low exhaust emissions in recent years. In general, most of these alternative fuels have high volatility and flash-boiling takes place easily in fuel spray, when they are injected into the combustion chamber of an internal combustion engine under high pressure. In addition, fuel design concept the multicomponent fuel with high and low volatility fuels has been proposed in the previous study in order to control the spray and combustion processes in internal combustion engine. It is found that the multicomponent fuel produce flash-boiling with an increase in the initial fuel temperature. Therefore, it is important to investigate these flash-boiling processes in fuel spray.

In the present study, the sub models of flash-boiling spray are constructed. This sub model considers the bubble nucleation, growth and disruption in nozzle orifice and injected fuel droplets. Therefore, the model is implemented into KIVA3V and the spray characteristics of multicomponent fuel with and w/o flashing are numerically investigated. In addition, these numerical results are compared with experimental data which were obtained in the previous study using a constant volume vessel. The flashing spray characteristics from numerical simulation qualitatively shows good agreement with the experimental results. Especially it is confirmed from both the numerical and experimental data that flash-boiling effectively accelerates the atomization and vaporization of fuel droplets. This means that lean homogeneous mixture can be briefly formed by using flash-boiling in combustion chamber.