No abstract

Oil-soluble ionic liquids (ILs) have recently been demonstrated as effective lubricant additives of friction reduction and wear protection for sliding contacts. However, their functionality in mitigating rolling contact fatigue (RCF) is little known. Because of the distinct surface damage modes, different types of surface protective additives often are used in lubricants for sliding and rolling contacts. Therefore, the lubricating characteristics and mechanisms of ILs learned in sliding contacts from the earlier work may not be translatable to rolling contacts. This study explores the feasibility of using phosphonium-phosphate, ammonium-phosphate, and phosphonium-carboxylate ILs as candidate additives in rolling–sliding boundary lubrication, and results suggested that an IL could be either beneficial or detrimental on RCF depending on its chemistry. Particularly, the best-performing phosphonium-phosphate IL at 2% addition made a low-viscosity base oil significantly outperform a more viscous commercial gear oil in reducing the RCF surface damage and associated vibration noise. This IL generated a thicker, smoother, and more homogeneous tribofilm compared with commercial additives, which is likely responsible for the superior RCF protection. Results here suggest good potential for using appropriate IL additives to allow the use of low-viscosity gear and axle fluids for improved efficiency and durability.

Abstract:As alternative lubricant anti-wear additives are sought to reduce friction and improve overall fuel economy, it is important that these additives are also compatible with current emissions control catalysts. In the present work, an oil-miscible phosphorous-containing ionic liquid (IL), trihexyltetradecylphosphonium bis(2-ethylhexyl) phosphate ([P 66614 ][DEHP]), is evaluated for its impact on three-way catalysts (TWC) and benchmarked against the industry standard zinc-dialkyl-dithio-phosphate (ZDDP). The TWCs are aged in different scenarios: neat gasoline (no-additive, or NA), gasoline+ZDDP, and gasoline+IL. The aged samples, along with the as-received TWC, are characterized through various analytical techniques including catalyst reactivity evaluation in a bench-flow reactor. The temperatures of 50% conversion (T50) for the ZDDP-aged TWCs increased by 30, 24, and 25˝C for NO, CO, and C 3 H 6 , respectively, compared to the no-additive case. Although the IL-aged TWC also increased in T50 for CO and C 3 H 6 , it was notably less than ZDDP, 7 and 9˝C, respectively. Additionally, the IL-aged samples had higher water-gas-shift reactivity and oxygen storage capacity than the ZDDP-aged TWC. Characterization of the aged samples indicated the predominant presence of CePO 4 in the ZDDP-aged TWC aged by ZDDP, while its formation was retarded in the case of IL where higher levels of AlPO 4 is observed. Thus, results in this work indicate that the phosphonium-phosphate IL potentially has less adverse impact on TWC than ZDDP.

Energy efficient lubricants are essential for sustainable transportation, and the trend is to develop and implement lower viscosity lubricants with more effective additives. Ionic liquids (ILs) have been reported as candidate additives with superior friction and wear reducing capabilities. Unlike most literature relying on bench-scale testing of simple oil−IL blends, this study produced low-viscosity (SAE 0W-12) fully formulated engine oils using a phosphonium-organophosphate IL as an antiwear additive and evaluated them in both bench-scale tribological testing and full-scale fired engine dynamometer testing. The experimental formulation containing a combination of ZDDP and IL outperformed the formulations using either ZDDP or IL alone, as well as a commercial SAE 0W-20 engine oil in terms of mitigating boundary friction, wear, and contact fatigue-induced micropitting. Racing engine dynamometer tests demonstrated 3−4 °C lower oil temperature, 4−5 ft-lbs higher horsepower output, and up to 9.9% better fuel economy for the IL-containing SAE 0W-12 experimental oil compared with selected commercial SAE 5W-30 and 0W-20 engine oils.