Fuel lubricity is an essential property that ensures the longevity end efficiency of diesel CI engines. Nanomaterials have been shown to have the potential to improve lubricity in many different lubricating substances, including fuels. Moreover, the combustion process has also been shown to improve with the introduction of nanomaterials. This study investigated a series of nanoparticles, including carbon nanoplates, carbon nanotubes, aluminum oxide, zinc oxide, and cerium oxide, as lubricity-enhancing additives for selected fuels. Conventional diesel fuel and rapeseed oil methyl ester, referred to as biodiesel, were chosen as base fuels for modification. The lubricity was evaluated according to the standard test method ASTM 6079 using the HFRR tribometer. The leading lubricity indicators were the wear scar diameter, wear volume, and coefficient of friction. In addition, the worn surface analysis was performed to elucidate the lubrication mechanism. The results show that the addition of nanoparticles can improve the lubricity of both investigated fuels. However, the effect differed among nanoparticles and fuels. In summary, carbon nanotubes could be a rational choice for both fuels. In addition, zinc oxide improved the lubricity of diesel fuel, while carbon nanoplatelets and aluminum oxide nanoparticles showed improvements in the lubricity of biodiesel.

The appearance, evolution, and proliferation of electric-vehicle motors have introduced new challenges for lubricants. The appearance of electric currents in the shafts of electric motors can dramatically change the original properties of lubricated contacts, leading to mechanism failure. Understanding and controlling this phenomenon can be advantageous for lubrication, but investigating the lubricants requires specific equipment and conditions. Therefore, in this study, we introduced a ball-on-plate reciprocating tribometer capable of applying electric voltage to the elements of the friction pair and measuring the electric contact resistance (ECR) as feedback. Mineral-based paraffin oil was used as a lubricant in this study. The coefficient of friction (COF), wear, surface morphology, and composition were analysed. It was found that high-speed ECR measurement could give valuable information regarding the lubrication conditions in reciprocating friction pairs. This study shows that even tiny currents flowing through the tribo contact can alter the lubricating conditions. Moreover, the polarity of the applied voltage is also of great importance. Applying negative voltage to the harder surface can significantly increase wear if the tribo-film is based on surface oxidation.

Recently, environmentally friendly lubricants and their additives have been of great interest. Using such lubricants can provide a few benefits, namely: nontoxicity and biodegradability when exposed to groundwater or soil. Moreover, renewable raw materials could be used to produce these lubricants. This study aims to synthesize bis (2-hydroxyethyl)ammonium erucate protic ionic liquid containing a renewable counterpart-erucic acid. The synthesis of bis (2-hydroxyethyl)ammonium erucate, its physical properties, solubility in the base lubricating fluid, and tribological properties were evaluated. The study shows that even though the investigated protic ionic liquid is liquid at room temperature, it has a very high kinematic viscosity, which drops when the temperature increases. Bis (2-hydroxyethyl)ammonium erucate can be dissolved in water up to 3 wt%. It also has excellent lubricity when used as a neat lubricant and could be successfully applied as a lubricity-enhancing additive in water.

Water-based lubricating fluids (WBLFs), known for their significant environmental benefits, are the focus of this study. The properties of WBLFs directly influence lubricated mechanisms’ longevity and operating efficiency. WBLFs are enhanced using additives, which must improve their properties and, at the same time, remain environmentally friendly. This study combines bis(2-hydroxyethyl) ammonium erucate protic ionic liquid and titanium oxide nanoparticles to formulate the hybrid additive. The lubricity was investigated using Alumina/Bearing steel and WC/Bearing steel friction pairs in a reciprocating ball-on-plate tribo-tester. The results show that protic ionic liquid can significantly improve lubricity and the corrosion-preventing ability of the base fluid. Applying a hybrid additive further improved the wear reduction ability in the WC/Bearing steel friction pair. However, the wear reduction ability was diminished when a hybrid additive was used to lubricate the Alumina/Bearing steel friction pair. The proposed lubricity improvement mechanism is based on forming an adsorption layer of ionic liquid molecules and rolling and tribo-sintering titanium oxide nanoparticles.

Owing to their low cost and environmentally friendly nature, water-based lubricants have benefits over oil-based ones. However, the appropriate additive package is indispensable in improving its tribological properties. In the current study, we have investigated the friction and wear reduction ability of bis(2-hydroxyethyl) ammonium oleate protic ionic liquid (PIL) in a glycerol aqueous lubricating fluid. The tribo-tests were performed using a ruby–steel friction pair acting in reciprocation mode. The coefficient of friction and wear were the main characteristics of the evaluation. Analysis of the physical properties of the investigated lubricating samples and worn surface analysis were performed to reveal a more detailed picture. The study shows that the investigated PIL can significantly reduce friction and wear. The most suitable concentration of PIL was 0.5%, where friction and wear were reduced 2.6 and 15.8 times, respectively. Using the investigated PIL facilitates a sliding coefficient of friction as low as 0.039. It was hypothesized that the formation of the adsorption layer and metal soap was responsible for this. Further studies could be directed toward higher load and speed applications.