AUTOMOTIVE PCEO
Fuel Economy: An important outlook
Dr. Raj Shah, Director and Ms. Mrinaleni Das, Senior Intern, Koehler Instrument Company, and Ken Hope, Ph.D., CLS, Global PAO Technical Services Manager, Chevron Phillips Chemical Company and STLE Immediate Past-President
The automobile industry’s rapid growth and innovation were fueled by the contribution of friction, a key factor in improving performance. However, modern cars’ safety features and the competition to provide the best features to consumers have led to a significant increase in car weight, resulting in an increase in fuel consumption and friction. Between 1990 and 2005, fuel consumption in cars increased by 37%, with road transportation contributing 75-89% of total CO2
approximately 20% of global emissions.
As concerns over carbon emissions are on the rise, especially after regulations such as the Safe Affordable Fuel-Efficient (SAFE) Vehicles Rules have been implemented, the need for sustainable practices is more necessary than ever. Tribologists have proposed the use of low-viscosity lubricants to improve fuel economy and reduce carbon footprint. However, using low-viscosity lubricants can also increase wear and tear on vehicles, making it important to find the optimal concentration of lubricating oil to balance fuel economy, friction, and wear. This paper aims to explore current research on lubricating oils and shed light on this issue.
The effectiveness of lubricating oil depends on the type of lubricant regime involved (e.g., boundary lubrication, mixed lubrication, hydrodynamic lubrication, and elastohydrodynamic lubrication). Low-viscosity engine oils are designed to reduce viscous drag during hydrodynamic or elastohydrodynamic lubrication conditions, where the oil film thickness is large enough to separate the two sliding surfaces completely. However, low-viscosity oils are more prone to shear thinning at high temperatures and thinning at lower temperatures, causing the lubricating film thickness to decrease. As the film thickness decreases, the lubrication regime shifts towards mixed and boundary lubrication, where the oil film cannot overcome the surface roughness.
18 LUBE MAGAZINE NO.175 JUNE 2023 Figure 1: North American Viscosity Grade Trend [4]
Over the years, heavy-duty diesel (HDD) saw a sharp rise in sales, and therefore, it is important to discuss the viscosity trend associated with these vehicles. Currently, there is a rise in SAE 15W-40’s market share. However, it is predicted to decline to 30%, and SAE 10W-30 is all set to take over the market. However, one of the main concerns associated with these low-viscosity oil grades is that they can lead to oil volatility and ruin and affect necessary characteristics.
Traditionally, the European market has favoured slightly heavier oils compared to North America. In Europe,
emissions in the transportation sector and
Across North America, SAE 5W-30 has been the most popular oil grade for the existing automobile market since the 1980s, making up 40% of the total oil sold in the North American Market. However, it is gradually being replaced by SAE XW-20, a lower-viscosity oil grade. The implementation of ILSAC GF-6B allowed the introduction of new fuel economy viscosity grades below SAE 0W-20 to be introduced with their own certification mark. Figure 1 shows by 2025, SAE 0W-20 is expected to control 50% of the oil market share in the North American region.
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