The effect of different n-butanol-fatty acid methyl esters (FAME) blends on puffing characteristics

- The temperatures of BUT25, BUT50 and BUT75 were similar at the start and end of the transient heating phase.
- The temperature growth rate of BUT75 was significantly lower than that of BUT00, BUT25 and BUT50.
- The fluctuation evaporation phase could be divided into the strong and weak fluctuation stages.
- The active and passive ruptures were observed in the fluctuation evaporation phase.
- The similarity degree of BUT75 exhibited a comb-like structure in the strong fluctuation stage.

The droplet suspension technology was used under the condition of atmospheric pressure and 873 K. The n-butanol concentration ranged from 0% to 75% to investigate the effect of n-butanol concentration on the puffing characteristics of a n-butanol-fatty acid methyl esters (FAME) droplet. Experimental results showed that BUT25, BUT50 and BUT75 (BUT'XX' represented XX% n-butanol by mass fraction in the n-butanol-FAME blend) underwent three phases, namely the transient heating phase, fluctuation evaporation phase and equilibrium evaporation phase. The temperatures of BUT25, BUT50 and BUT75 were similar at the start and end of the transient heating phase. The duration of BUT75's transient heating phase was much longer than that of BUT25 and BUT50. Therefore, the evaporation cooling of BUT75 was the most prominent because the temperature growth rate of BUT75 was significantly less than that of BUT25 and BUT50. Furthermore, the fluctuation evaporation phase could be divided into the strong and weak fluctuation stages. The violent fluctuation was only observed in the strong fluctuation stage. The weak fluctuation stage was similar as the stable evaporation. The active rupture was found in the strong fluctuation stage and the passive rupture was found in the weak fluctuation stage. The active and passive ruptures were caused by the fast bubble expansion and surface evaporation respectively. In addition, many periodic processes were contained in the strong fluctuation stage. The similarity degree of the periodic process showed a slump and a gradual increase, which were caused by bubble expansion and droplet recovery respectively. The bubble expansion of BUT50 was greater than that of BUT75. Significant bubble expansion led to the violent deformation after bubble rupture. The recovery time of BUT50 was longer than that of BUT75. Therefore, the similarity degree of BUT50 exhibited a wavy structure and BUT75 displayed a comb-like structure in the strong fluctuation stage.