Investigation of biosurfactant dosage on water-in-biodiesel fuel spray characteristics and a microscopic spray of water-in-biodiesel droplet micro-explosion

Water-in-biodiesel emulsions lower exhaust temperatures and enhance fuel-air mixing through micro-explosion, thereby reducing the emission and improving the combustion simultaneously. Biosurfactants are poised to play key role in the future of diesel engine technology. The integration of biosurfactants in water-in-diesel emulsions represents a significant step in developing eco-friendly, efficient fuel technologies. This study is one of the foremost attempts to examine biosurfactant in water-in-biodiesel microscopic spray at elevated temperatures. A series of water-in-biodiesel emulsions with varying biosurfactant concentrations (1–3%) were tested in a constant-volume combustion chamber under evaporating conditions. High-speed cameras with two lenses visualized spray characteristics and droplet micro-explosions. Custom Python and MATLAB algorithms were developed for precise spray measurements. Findings show that increasing biosurfactant concentration in emulsified fuel to 1 %, 2 %, and 3 % increases spray penetration by 51 %, 55.8 %, and 62.8 %, respectively, compared to base fuel, and increases the dispersion angle from 4.81 % to 6.61 % and 16 %. Additionally, a decrease in droplet size distribution is observed with an increase in biosurfactant concentration, suggesting delay in puffing/micro-explosion occurrence. Three nearly identical droplets of same fuel, 111.2 μm, 112 μm, and 114.3 μm, experienced different micro-explosion times: 1250 μs, 1400 μs, and 1850 μs, respectively, suggesting variability in fuel composition.