Lubricants & energy efficiency: Life-cycle analysis

Abstract

The use of optimised lubricants can lead to significant energy savings (i.e. reduced fuel or electricity costs) and also reduced C02 emissions. Over the last 20–30 years, the drive to improve vehicle fuel consumption has led to the widespread availability of fuel economy lubricants (e.g. friction modified SAE 5W-30 grades compared to SAE 15W-40 grade lubricants). Over realistic driving cycles, vehicle fuel consumption can in some circumstances decrease by between 2–5% when fuel economy lubricants are used. For cold-start, short-trip driving, the fuel economy improvement may be even higher still. Energy efficient lubricants are less widely used in industrial applications, but the potential savings may be even greater. For instance, in hydraulic systems, friction is dominated by pipe losses and is therefore directly proportional to lubricant dynamic viscosity (whereas in an engine friction is proportional to the square root of viscosity). Hence changing the ISO viscosity grade, or moving to a higher Viscosity Index (VI) lubricant could lead to significant energy savings under cold-start conditions. Similarly, in gear lubricants, it is known that in moving from mineral base-stocks to more highly processed base-stocks, the decrease in the pressure-viscosity coefficient of the lubricant results in both decreased friction and decreased temperature rises. In all these examples, the energy efficient lubricants are generally more expensive than conventional lubricants, and a life-cycle cost analysis, which takes account of operating costs as well as the initial purchase cost of the lubricant, is required to bring out the true benefits of these products. When the cost of C02 emissions becomes more apparent in future years, the life-cycle cost analysis will be weighted even more in favour of energy efficient lubricants.