Effect of flash boiling and air-assisted injection on methanol spray characteristics

The advantages of methanol as an alternative fuel have been well demonstrated. However, the difficulty of atomization restricts its practical application. Also, flash boiling and air-assisted injection have been shown to improve the atomization quality of fuels. In this work, the methanol spray characteristics with and without air assistance were experimentally investigated. The experimental conditions include flash-boiling and non-flash-boiling states. High-speed backlight imaging and a Malvern laser particle size analyzer were used to obtain the spray images and droplet sizes, respectively. The flash-boiling state caused a significant variation in spray morphology and the formation of high-concentration central plumes with greater velocity. Compared to the non-flash-boiling spray, the droplet size of the central plumes is larger, whereas the peripheral droplets have a smaller particle size. The droplet size of the air-assisted spray at normal temperature and pressure can reach approximately 3.5 μm, whereas that of the methanol spray without air assistance under a strong flash-boiling state is approximately 60 μm, indicating that air-assisted injection can significantly improve the atomization quality of methanol spray. Furthermore, because of the good atomization, the air-assisted methanol spray is significantly affected by evaporation at high temperatures, and no significant transition of a flash-boiling state was observed.