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One of the technical possibilities to enhance the properties of lubricants and biolubricants is dispersing nanoparticles in them. Although conceptually simple, this operation faces challenges related to: (1) obtaining an initial good dispersion of the nanoparticles in the liquid and (2) ensuring the stability of this dispersion to avoid coalescence. The objective of this study is to verify possible improvements of the stability and characteristics of conventional and bio-based lubricants by efficiently dispersing in them surface-modified SiO2 nanoparticles. The silane coupling agent KH570 was utilized to modify the surface properties of SiO2 nanoparticles, facilitating their dispersion within the lubricants. Nanolubricants and nanobiolubricants were prepared using a two-step technique. The dispersion stability of these lubricants was assessed using sedimentation photography, FTIR, and UV-Vis spectrophotometric analyses. The addition of SiO2 nanoparticles resulted in enhanced physicochemical properties of the resulting lubricant, including slight increases in density and viscosity, as well as a higher viscosity index. Chemical analyses, such as TAN and TBN measurements, confirmed that the nanoparticle addition at various concentrations (0.25%, 0.5%, 0.75%, and 1.0%) did not introduce critical acidity levels or compromise the alkaline reserve. ICP-OES analysis indicated minimal impact on essential additive concentrations, supporting the feasibility of SiO2 nanoparticles in enhancing lubricant properties without destabilizing additives. The stability of the nanolubricants was monitored over 77 days, with visible sedimentation beginning around the 30th day and becoming more pronounced by the 54th and 77th days. Bio-lubricants exhibited slightly higher sedimentation than conventional lubricants. Optimizing the sonication time proved to be crucial, with longer sonication times (2.5 h) significantly improving the stability of nanolubricants across various concentrations of added nanoparticles. FTIR analysis confirmed the presence of SiO2 and KH570, indicating no alteration to the basic functional structures of the lubricants and biolubricants. UV-Vis spectrophotometry further underscored the importance of optimizing sonication time for enhanced stability. Overall, this study demonstrates that incorporating surface-modified SiO2 nanoparticles enhances the properties and stability of conventional and biolubricants, offering potential for improved performance in industrial and engine applications. [ABSTRACT FROM AUTHOR]

The need for the decarbonization of heavy-duty vehicles requires a deep understanding about the effects of biofuels, which represent a viable pathway to cut the emissions in the hard-to-abate sectors, like agricultural tractors. A novel meta-analysis approach can help to thoroughly investigate the effects of biodiesel blends on farm tractor engines in terms of performance and emissions. Studies were identified using the main keywords related to internal combustion engines in prominent scientific databases. Standardized mean differences were calculated for each study to evaluate engine performance and gas emissions. Mixed-effects regression models were developed to investigate performance and environmental pollution changes over different biodiesel blending ratios, biodiesel sources, and engine types. The analysis revealed significant effects of biodiesel blending ratio on decreasing torque [−13.0%, CI 95% (6.7%–19.3%); I2 = 97.67; p = 0.000; Q = 129.94], engine power [−15.0%, CI 95% (10.0–20.0%); I2 = 54.82; p = 0.000; Q = 101.81], CO2 emissions [−24.1%(15.0–32.0%); I2 = 0.198; p = 0.000; Q = 20.04], and CO emissions [−17.5%, CI 95% (16.0–18.0%); I2 = 98.62; p = 0.000; Q = 97.69], while increasing specific fuel consumption [+5.2%, CI 95% (1.0–9.0%); I2 = 95.94; p = 0.000; Q = 129.74] and NO emissions [+11.0%, CI 95% (6.0–15.0%); I2 = 98.51; p = 0.000; Q = 157.56]. The same analysis did not show any influence of the sources of biodiesel and the engine type. Finally, meta-regression found a significant positive association between increasing ratios of biodiesels and decreasing torque, engine power, CO and CO2 emissions, and increasing fuel consumption and NO emissions in terms of linear equations. Although through these equations it is not possible to individuate an optimal range of blending ratios able to lower the emissions and not affect the engine parameters, the range from 9.1% to 13.0% of biodiesel is a good tradeoff. Within it, the only decrease in engine performance is in charge of the power, however contained within 4%, while CO and CO2 emissions are reduced (respectively by 0.0%/−2.8% and −3.6%/−6.0%) without using any specific pollutant abatement systems. [ABSTRACT FROM AUTHOR]