Visual research on spray and low temperature combustion of biodiesel/ethanol/water micro-emulsified fuels

To solve the negative environmental problems derived from the transport sector, this study is devoted to realizing a thorough substitution of biomass fuels for petroleum diesel. The spray, ignition, combustion, and emission of pure biodiesel, biodiesel/ethanol blend, and two kinds of biodiesel/ethanol/water triple micro-emulsified fuels were studied through optical visual methods on a constant volume combustion chamber. First of all, the micro-emulsified fuels obviously improve the spray quality. The micro-explosion effect of internal water improves the spray and atomization and the gas–liquid phase spray projected areas of microemulsion fuel at the maximum water blending ratio are the largest in the mid and late stages of spray. Secondly, with the increase of the water blending ratio, the combustion process of the fuel is improved. The flame lift-off length increases, the ignition delay period is prolonged, and the air entrainment effect is enhanced. Meanwhile, the combustion flame temperature decreases with the increase of water content, realizing low-temperature combustion. Lastly, the micro-emulsified fuels markedly decrease soot emissions. Both the total luminous intensities and normalized total KLs of micro-emulsified fuel with high water content are the lowest, achieving the best soot reduction effect. The triple micro-emulsified fuels have significant potential as a full biomass alternative fuel.