Study on the effect of soot generation from metal oxide/biodiesel nanofluid fuel combustion

With the depletion of fossil fuels and the escalating concerns over environmental degradation, the global focus has shifted towards renewable energy sources and stricter emission regulations. Biodiesel, a low-carbon and environmentally friendly renewable fuel, has garnered considerable attention. However, given its low fuel performance, recent studies have focused on the mixed use of additives. Concurrently, advances in nanotechnology have prompted exploration into the application of nanoparticles in biofuels. This study investigated the effect of different metal oxide nanoparticles on soot generation during biodiesel combustion. Nanofluidic fuels were prepared, and soot particles were collected using direct sampling. The physicochemical properties of these particles were analyzed using FTIR, XRD, HRTEM, and RS techniques. The findings revealed that metal oxide nanoparticles influenced several properties of soot particles, including functional groups, microcrystalline structure parameters, particle size distribution, fringe spacing, and the degree of structural disorder. The strength of oxygen-containing functional groups in soot particles increased variably across different nanoparticle types. The particles of polycyclic aromatic hydrocarbons (PAHs), an intermediate product of nanofluid fuel combustion that generates soot particles, were smaller by at least 0.1 nm compared to those of B100. The average particle sizes of soot were smaller than those from B100 (less than 10.99 nm). The number of particles in the 3–6 nm size range increased considerably, while the number of those in the 12–18 nm range decreased notably. Additionally, the size of more than 50 % of particles in the 9–14 nm range decreased to the 5–10 nm range. The fringe separation distance increased to varying degrees across different nanoparticle properties, with the highest frequency at 0.22 nm. Notably, more than 11 % of the streak separation distances were approximately 0.22 nm, with an increase in number approaching 5 % in the 0.24 nm range and a decrease in number to zero in the 0.14–0.16 nm range. The microcrystalline parameters exhibited substantial changes, with an increase in disordered structures and PAHs defects. The catalytic and oxidative effects of metal oxide nanoparticles enhanced soot oxidation activity, reduced soot emissions, and promoted more complete fuel combustion. The effectiveness of the nanoparticles in improving combustion performance followed the order: CuO > Fe3O4 > TiO2 > Al2O3. This improvement was primarily attributed to variations in the specific surface area and oxidant-supplying capacity of the four metal oxides. Overall, this study provides a promising approach for achieving cleaner combustion of biodiesel and highlights the potential of metal oxide nanoparticles in reducing soot emissions, offering significant practical applications and environmental benefits.