Quantitative study on the influence of bubble explosion on evaporation characteristics of flash boiling spray using UV-LAS technique

Flash boiling is an effective way to enhance both atomization and evaporation characteristics of liquid fuel spray by introducing explosion of vapor bubbles, compared with the conventional high pressure injection. However, the evaporation characteristics and mechanism of flash boiling spray, especially, that associated with the explosion of vapor bubbles at high superheat degree, is still unknown. In this study, the vapor and liquid mass distributions in flash boiling sprays were quantified by use of ultraviolet/visible laser absorption/scattering (UV-LAS) imaging technique over a broad range of superheat degree. Based on the results of macro-structure characteristics of liquid/vapor phase spray and total evaporated vapor mass, influence of bubble explosion on detailed evaporation characteristics of flash boiling spray are investigated. And, by associating with our previous work on breakup mechanism of superheated droplet and liquid jet, the effect of two evaporation regimes, namely surface evaporation and flashing evaporation, on evaporation of flash boiling spray has been successfully identified for the first time. These results provide insightful information for understanding the evaporation mechanism of a superheated liquid jet and modeling a flash boiling spray.