Experimental Study of Droplet Combustion and Flame Characteristics of B₂O₃ Nanoparticle-Doped Algae Biodiesel Blends

The increasing depletion of fossil fuel reserves and the growing concern regarding greenhouse gas emissions have accelerated the search for sustainable alternative fuels suitable for compression ignition engines and advanced combustion systems. Among various renewable fuels, algae biodiesel has emerged as one of the most promising third-generation biofuels owing to its high lipid productivity, rapid growth rate, non-competition with food crops, and ability to utilize wastewater and carbon dioxide during cultivation. Despite these advantages, algae biodiesel exhibits relatively higher viscosity, lower volatility, and slower evaporation characteristics than conventional diesel fuel, leading to prolonged ignition delay, reduced combustion efficiency, and increased soot formation during droplet combustion. These limitations necessitate innovative approaches to enhance fuel atomization and combustion behavior without extensive engine modifications. Nanotechnology has recently attracted considerable attention in fuel combustion research because nanoparticles possess exceptional thermal conductivity, catalytic activity, oxygen buffering capability, and high surface-area-to-volume ratio. Among numerous metal oxide nanoparticles, boron oxide (B₂O₃) has demonstrated significant potential for improving oxidation reactions, increasing heat transfer rates, and enhancing flame stability. The incorporation of boron oxide nanoparticles into algae biodiesel blends is expected to accelerate droplet evaporation, promote secondary atomization through micro-explosions, shorten ignition delay, improve flame propagation, and reduce pollutant precursor formation. However, comprehensive investigations on droplet-scale combustion characteristics of algae biodiesel doped with boron oxide nanoparticles remain limited in literature. The present study investigates the influence of boron oxide nanoparticles on the droplet combustion characteristics of algae biodiesel–diesel blends under atmospheric conditions using a single suspended droplet combustion apparatus. Boron oxide nanoparticles were dispersed into an algae biodiesel blend using ultrasonic homogenization at different concentrations to obtain stable nanofuels. The combustion characteristics were evaluated using a high-speed imaging system coupled with optical diagnostics for recording flame evolution, droplet regression, ignition delay, flame height, flame diameter, burning rate constant, droplet lifetime, and soot luminosity. The temporal variation of droplet diameter followed the classical D²-law, while image processing techniques were employed to quantify flame geometry throughout the combustion process. The investigation aims to establish the relationship between nanoparticle concentration and combustion enhancement by examining the effects of catalytic oxidation, thermal conductivity improvement, and localized heat release mechanisms. Particular emphasis is placed on identifying the optimum nanoparticle concentration that maximizes burning rate while maintaining flame stability and minimizing soot generation. The study also discusses the occurrence of puffing and micro-explosion phenomena caused by differential volatility between diesel and algae biodiesel components, which are further intensified by the presence of nanoparticles. The findings of this investigation are expected to provide valuable insights into the design of advanced algae-based nanofuels for future clean combustion systems. Enhanced droplet combustion characteristics achieved through boron oxide nanoparticle addition may contribute toward improved thermal efficiency, lower ignition delay, reduced particulate emissions, and better combustion stability in practical diesel engines and gas turbine combustors. The outcomes also provide fundamental combustion data that can support computational modeling and optimization of nanoparticle-assisted renewable fuels.