Influence of deposit on spray behaviour under flash boiling condition with the application of closely coupled split injection strategy

•Deposit causes small cone angle and long penetration due to poor atomization.•Deposit raises SMD by increasing droplet size and lowering breakup potential.•Split injection strategy effectively lowers the impingement possibility.•Split injection alleviates the adverse effect of deposit under flash boiling.

The effects of deposit on the spray macroscopic characteristics and droplet behaviour under flash boiling condition were investigated through high speed imaging and Phase Doppler Particle Analyzer (PDPA) techniques. Closely coupled split injection strategy was tried to alleviate the negative effect of deposit on spray characteristics. It was found that with single injection strategy, deposit led to smaller cone angle and longer penetration due to poorer atomization and dispersion. Deposit also resulted in larger droplet size by introducing large droplets and lowering the potential of further breakup into small ones. When split injection strategy was employed under non-flash boiling condition, the effects of deposit of on the over-penetration and the resultant high potential of impingement were alleviated, while the negative effect of deposit on droplet size was enhanced. However, when split injection was used under strong flash boiling condition, the negative influence of deposit on the spray over-penetration was significantly alleviated and the negative impact on the droplet size was almost eliminated although reduced potential for large droplets to further break up was still found. The employment of optimal split injection strategy is believed to be important for the alleviation of the adverse effect of deposit on the spray characteristics and the emissions.