Knowledge

The aim of this work was to compare the surface adsorption and lubrication properties of plant and dairy proteins. Whey protein isolate (WPI) and pea protein isolate (PPI) were chosen as model animal and plant proteins, respectively, and various protein concentrations (0.1–100 mg/mL) were studied with/without heat treatment (90 °C/60 min). Quartz crystal microbalance with dissipation monitoring (QCM-D) experiments were performed on hydrophilic (gold) and hydrophobic polydimethylsiloxane (PDMS) sensors, with or without a mucin coating, latter was used to mimic the oral surface. Soft tribology using PDMS tribopairs in addition to wettability measurements, physicochemical characterization (size, charge, solubility) and gel electrophoresis were performed. Soluble fractions of PPI adsorbed to significantly larger extent on PDMS surfaces, forming more viscous films as compared to WPI regardless of heat treatment. Introducing a mucin coating on a PDMS surface led to a decrease in binding of the subsequent dietary protein layers, with PPI still adsorbing to a larger extent than WPI. Such large hydrated mass of PPI resulted in superior lubrication performance at lower protein concentration (≤10 mg/mL) as compared to WPI. However, at 100 mg/mL, WPI was a better lubricant than PPI, with the former showing the onset of elastohydrodynamic lubrication. Enhanced lubricity upon heat treatment was attributed to the increase in apparent viscosity. Fundamental insights from this study reveal that pea protein at higher concentrations demonstrates inferior lubricity than whey protein and could result in unpleasant mouthfeel, and thus may inform future replacement strategies when designing sustainable food products.

This invention involves the development of less corrosive, high performing organomolybdenum compounds with applications as additives in lubricants. Lubricants containing these compounds have demonstrated improved performance with respect to friction reduction, wear protection, and copper and lead corrosion, in particular for diesel and passenger car engine oil applications where high performing, more durable additives are required in terms of oxidative and hydrolytic stability.

An improved organic and molybdenum friction modifier combination is disclosed, the combination resulting in a synergistic result of both initial friction reduction performance and a further retention and durability of continued friction reduction performance. These results will produce added benefit from, e.g., formulated passenger car motor oils targeting lower viscosity formulations to help improve fuel economy.

In Europe, recent regulations on advanced biofuels have prompted a search for new fuel sources and the development of synthesis methods meeting the demanding specifications of the sector. However, in developing countries such as Algeria, where a significant stock of frying oil is unused, the use of diesel engines powered with waste-oil-derived biofuels must be explored. In this work, the variables related to the transesterification reaction from this frying oil with ethanol are analyzed using response surface methodology. From this analysis, only the reaction time and temperature have been determined as relevant parameters. In addition, FT-IR analysis has proven a useful tool to analyse the conversion in the transesterification reaction of waste frying oil with ethanol and is cheaper and quicker than GC-FID. This sustainable biofuel (FAEE), mixed with a diesel and pure fuel, has been physically characterized. The mixture of FAEE at 30% by volume with diesel meets the requirements demanded in standard EN 590 and can be classified as winter diesel class D. As a pure biofuel, only its high cold flow temperatures could constitute a drawback for exporting to temperate climates but not for internal consumption.

The tribological performance of AISI 52100 substrates subjected to several surface treatments have been evaluated in rolling, sliding, and mixed mode contact. The surface treatments include a boron-doped diamond-like carbon (B-DLC) coating deposited by plasma-assisted magnetron sputtering, an ultrasonic nanocrystal surface modification (UNSM) technique used to generate severe plastic deformation in the near surface of the steel specimens, and a B-DLC coating applied to a UNSM pretreated surface. In general, the tribological performance of the duplex surface treatment was superior to that of the untreated specimens and of the specimens with the other surface treatments in rolling, sliding, and mixed mode contact. The improved tribological performance of the duplex process was attributed to the combination of increased wear resistance provided by the B-DLC coating and the grain refinement of the martensitic structure of the AISI 52100 imparted by the UNSM process that created a beneficial substrate/coating interface.

Model non-Newtonian fluids are used to determine the influence of fluid rheology on friction between viscoelastic substrates. We uniquely designed two groups of fluids to be iso-viscous at low- and high-shear rate respectively using nanocellulose dispersions. While high-shear viscosity defines the elastohydrodynamic (EHL) region, below this limit a secondary transition in the Stribeck curve is found to be influenced by the low-shear viscosity; this is more pronounced for rough substrates and absent for Newtonian lubricants. We consider this to indicate that viscosity at low shear rates surprisingly has a strong influence on micro-EHL as well as fluid entrainment and complex fluid-asperity interactions in the boundary-mixed regimes. A conceptual model is proposed for non-Newtonian fluids in soft-lubrication.

The aim of this paper is the assessment of the possible impacts of eco-friendly fuels on injection systems by conducting tribological model tests. In this regard, lubricity (High-Frequency Reciprocating Rig, HFRR), scuffing load at different temperatures, and oxidation stability of different fuels B7, R33, pure HVO, and commercial-grade HVO diesel fuel have been deeply investigated.
As a result of our study, the HFRR wear scar diameter (WSD) shows no distinct temperature dependence for both fossil-based diesel fuels (B7 and R33). In contrast, vegetable-based ones (pure HVO and commercially available HVO-based fuel) reveal lower lubricity with a trend to higher HFRR value when the temperature is increased. The commercial HVO fuel shows, compared to the pure HVO, better HFRR values at all tested temperatures. Nevertheless, all HFRR values still stay within the limits set by the relevant fuel standards EN 590 and ASTM D975.
For all fuels, the scuffing load clearly depends on the temperature. B7 shows the highest and pure HVO the lowest scuffing load for all tested temperatures. At higher temperatures, commercially available HVO shows a similar, or even better, behavior compared to R33. The results indicate that there is no or only weak correlation between the HFRR and the scuffing load. This correlation obviously varies with fuel grades, additives, and other added substances.
HVO shows excellent oxidation stability due to its pure paraffinic character. Fossil fuels are less stable because aromatic hydrocarbons are much easier to crack than paraffins.
Combustion engines will continue to play an important role until the electrification of transportation is fully established. Our results show that alternative fuels like R33 and HVO represent good alternatives for fossil fuels in diesel engines.

The film-forming, friction and wear properties of a range of model and commercial ashless P and P/S antiwear additives have been studied. A method has been developed for removing the tribofilms formed by such additives in order to effectively quantify mild wear. In general the P/S additives studied formed thinner tribofilms but gave lower wear than the S-free P ones. In extended wear tests, three P/S additives gave wear as low, or lower, than a primary zinc dialkyldithiophosphate (ZDDP). For almost all lubricants tested the wear rate measured in short tests was considerably higher than that in long tests due to the greater contribution of running-in wear in the former. This highlights the importance of basing antiwear additive choice on reasonably long tests, where running-in becomes only a small component of the wear measured. It has been found that for both P and P/S ashless additives the addition of oil-soluble metal compounds based on Ti and Ca boosts tribofilm formation and can lead to very thick films, comparable to those formed by ZDDP. However, this thick film formation tends to be accompanied by an increase in mixed friction and also does not appear to reduce wear but may even increase it.

Low adhesion problem is one of the major problems for railways all over the world because this phenomenon can occur anytime and anywhere. To investigate when poor adhesion conditions can be expected in real operation, a ball-on-disc tribometer with a climate chamber was employed to simulate rolling-sliding contact under various environmental conditions. Clean and contaminated discs with leaf extract were used to simulate different surface conditions. Results indicate that contact operating under rolling-sliding conditions is more prone to the occurrence of low adhesion than found by others for pure sliding contact. Very low adhesion (≤0.05) were identified for contaminated and oxidized specimens operating under humid and wet conditions. For clean surfaces, low adhesion (≤0.15) were found under dew conditions.