Ultrasonic Preparation of Emulsions Derived from Aqueous Bio-oil Fraction and 0# Diesel and Combustion Characteristics in Diesel Generator

Preparation of emulsions from aqueous fractions of biomass pyrolysis liquid (bio-oil) and 0# diesel was studied under ultrasonic power. The thermogravimetric analysis and combustion characteristics of the optimized emulsions in a particular diesel generator were also investigated. The results show that the mass ratio of aqueous bio-oil fraction to 0# diesel affected the emulsion stability greatly, by factor analysis method, and the optimized emulsion was not stratified for 30 days when the ratio was 1:9 under the following conditions: water:bio-oil mass ratio, 2:1; ultrasonic time, 120 min; formula emulsifier addition (Span-80:Tween-80:Tween-20:n-octanol ratio = 72:9:9:10, wt %), 3 wt % (which was longer than that prepared by mechanical agitation). The density and heat value of the nonstratified emulsions (after 30 days) were similar with those of 0# diesel, because of the low aqueous bio-oil fraction content and wit diesel dilution; however, an increase of more than 38.4% in the dynamic viscosity and a decrease in pH from 5.26 to <3 may result from the concentrated polar oxygenates and carbohydrates in aqueous bio-oil fraction, which were further solubilized in water-in-oil (W/O) emulsion droplets. In addition, ultrasonic emulsification resulted in entropy augmentation and equilibrium tendencies (by thermodynamic analysis). Thermogravimetric analysis of the emulsion shows that there is a weight loss peak that is attributed to residual carbon combustion above 400 degrees C, in addition to a similar hydrocarbon vaporization peak at 180 degrees C with diesel. The existence of residual carbon and the high viscosity of the emulsion might have caused inefficient combustion when the output power of diesel generator was above 1400 W with high feeding amount, which also resulted in higher exhaust gas temperature than diesel feedstock, although microexplosion may have occurred. Moreover, when the output power increased to 1600 W with the emulsion used, the O-2 and NOx emissions decreased 21% and 87.2%, respectively, the CO2 emission increased 13.3%, and the CO and SO2 emissions increased quickly to 5124 ppm and 59 ppm, respectively, compared with pure diesel. The corrosion and blockage caused by coking of the injector were obvious.