Span80/Tween80 stabilized bio-oil-in-diesel microemulsion: Formation and combustion

A detailed experimental study was conducted to investigate the production and fuel properties of bio-oil-in-diesel microemulsion (BDM) and its emission characteristics. Bio-oil was produced from liquefaction of methanol, castor oil and sewage sludge. Hydrophilic surfactant (Span 80) and hydrophobic surfactant (Tween 80) of different mixing ratio and different co-surfactant (alcohols) were tested to form BDM with higher bio-oil solubility and better stability. The best mixed ratio was proved to be 7/3 (Span 80/Tween 80) with 2% n-hexanol. The principle of “likes dissolve likes” was set as a guiding mechanism on bio-oil solubilization process. The emulsified fuel stabilized by mixed surfactant and co-surfactant, in comparison with other hybrid fuels and diesel, was tested in a single cylinder, four-stroke, water cooling, direct injection, diesel engine to study the emission characteristics. The results show that, compared with diesel, BDM performed well in brake specific fuel consumption (BSFC) and brake thermal efficiency (BTE) while reduced CO, CO2 and NOX emissions by 21.4%-66.7%, 7.1%-27.3% and 1.5%-14.7%, respectively. This was the first time of using surfactant compound to form bio-oil microemulsion, which provides a possibility for practical application of microemulsion fuels and further benefiting SS utilization.