In the present work, the emulsion fuels from bio-oil heavy fraction and 0# diesel were prepared by mechanical and ultrasound emulsification technologies. The relationship between stable time of emulsions and HLB value of emulsifier was investigated. Results indicated that lower mechanical stirring speeds and lower ultrasonic amplitudes lead to longer stable time of bio-oil heavy fraction emulsions. The stable time of emulsions reduced as HLB values increasing, and it reached a maximal value of 14 minutes under a HLB value of 1.8. Zetasizer Nano S90 was adopted to measure the droplet distribution of emulsions. The major droplet size of emulsions was smaller than 90nm. Meanwhile, the droplet distribution curve of ultrasound emulsions was much complex than those of mechanical emulsions.

In this paper, emulsification study on bio-oil middle fraction and diesel was carried out. Mechanical and ultrasound emulsification technologies were used to prepare emulsion fuels between bio-oil middle fraction and diesel with different hydrophile and lipophile balance (HLB) values. It was found that the stability curve of emulsions had two peaks corresponding to the HLB values of 4.3 and 6, respectively. Comparable to the mechanical emulsions, the ultrasound emulsions had longer stable time. The stable time for ultrasound emulsions at the HLB values of 4.3 and 6 were 215 minutes and 143 minutes, respectively. Then the effects of surface tension and droplet size distribution on the stability of emulsions were investigated. It was found that the emulsion fuels with lower surface tension and smaller droplet size had longer stable time.