use of LVO does not lead to increased wear in EURO IV and CNG engines, as both candidate-low viscosity oils used in these engines showed similar wear performance to baseline oils.
However, it is important to keep in mind that Europe has been following the EURO VI standard, and EURO VII is already in the development phase. EURO VI CO permissible emission standard from EURO V but severely cut back on adequate NOx emission by the heavy-duty engines. Therefore, it is important to perform similar studies on EURO VI/VII engines to verify these claims. The adoption of advanced lubricants for heavy-duty diesel engines depends on OEM developments and field testing, with a more conservative approach due to durability concerns. The market penetration of lower-viscosity lubricants in the heavy-duty diesel segment may take longer compared to passenger car motor oils. Factors such as alternative fuels and advancements in electric vehicle technology also impact the future landscape for large diesel engines.
Another study led by Carden et al. found that baseline oil with the highest viscosity resulted in the least wear, and the amount of wear increased as the viscosity was decreased in the other oils. They used three different test oils in an IVECO Cursor 13 Euro V engine: a baseline 5W-30 oil with a kinematic viscosity of 12.28 mm2s-1 at 100 °C and compared them with low viscosity oil with a kinematic viscosity of 6.53 mm2s-1, and 4.82 mm2s-1. The lower viscosity oil caused micro-pitting, which was attributed to the ZnDTP additives used to protect against wear. The study mentioned that these micro pitting could be reduced by decreasing the concentration of ZnDTP in the oil or reducing the oil’s viscosity. Adding friction modifiers and blending PAO oil into the oil containing ZnDTP was also observed to mitigate the micro-pitting. Another option would be the inclusion of high-viscosity mPAO base oils as a viscosity modifier since this has been beneficial in racing applications.
Another study led by Tamura et al. suggested that friction modifier (FM) is essential as viscosity modification for next-generation engine oils to achieve better fuel economy. They studied several FMs, including molybdenum dithiocarbamate (MoDTC) and nonmetallic fatty compounds, to modify the boundary lubrication performance of engine oils. The addition of (FMs) reduces the friction coefficient, with MoDTC showing the lowest friction coefficient
among the FMs tested. However, MoDTC requires high temperatures to generate low-friction tribo-films based on MoS2, resulting in a temperature-dependent friction coefficient. Organic FMs show relatively small temperature dependence and statistical variation of friction coefficient compared to MoDTC, possibly because of the dynamic stability of adsorbed layers of organic FM molecules on the interfacial surfaces. The adsorption of organic FM molecules might be kinetically faster than the generation and growth of MoDTC-based tribo-films.
Further viscosity reductions can make a significant impact more recently due to the rise of diesel fuel prices. The retail price of Diesel, according to
www.eia.gov is $4.21/gallon as of March 2023. The savings for moving to lower viscosity engine oils for Class 8 over-the-road fleets is estimated to be “0.5% - 1.5% by switching from 15W-40 to 5W/10W- 30” according to Barrie Masters from Lubrizol [15], and this claim was sourced from Trucking Efficiency Confidence Report: Low-Viscosity Engine Lubricants from the North American Council for Freight Efficiency and Carbon War Room. The 0.5% to 1.5% of fuel economy from viscosity changes applied to a fleet will have substantial energy cost reduction. According to the ATA, there are currently 4.06 million Class 8 trucks in operation in 2021 and 38.9 million trucks registered for business purposes covering 302.14 billion miles and consuming 44.8 billion gallons of fuel. Saving 0.5% of the 35.5 billion gallons of diesel at the March average cost would be approximately $747 million in addition to the CO2
saved through the increased
efficiency. So even though the percentage of savings seems small, those numbers are by no means small when applied to just what is used here in the US.
The trend of reducing engine oil viscosity has resulted in decreased lubricating film thickness and increased risk of engine damage. Additives, such as friction modifiers (FMs), have been developed to address these issues. MoDTC, in particular, has shown a significant reduction in friction compared to other FMs. It is important for research to continue to address friction and wear risks, even as technology and regulations evolve.
www.koehlerinstrument.com
www.cpchem.com
For a full list of citations and references, please view the extended article on the Lube Media website
www.lube-media.com/digital-exclusives/
LUBE MAGAZINE NO.175 JUNE 2023
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