Lube-Tech PUBLISHED BY LUBE: THE EUROPEAN LUBRICANTS INDUSTRY MAGAZINE
No.99 page 3
Source: Infineum International Limited
from the late ‘80s until 2006 for it to reach this position. And, even though SAE 5W-20 and 0W-20 are now the most widely recommended grades for new cars, it will take a long time for SAE 5W-30 to exit the market.
Even as far out as 2020, SAE 0W-16 and below will account for a just small percentage of oil sold in North America – a picture likely to reflect global viscosity grade trends.
Low viscosity and durability The first formulation challenge presented by moving to lower viscosity lubricants is how to balance the desire for fuel economy with the need to protect the engine and all its components. The thinner oil films associated with low viscosity fluids mean it is harder for the oil to keep the loaded contact surfaces in the engine sufficiently apart from each other. This can lead to accelerated wear rates, and even locally increased friction. In our view, it makes little commercial sense to trade engine durability for fuel economy gains.
Infineum studies indicate that, in some engines, reducing lubricant viscosities to 2.3 HTHS presents little risk of engine component wear. Below this level, specific engine components, for example the top ring and bearings, observe higher wear rates. To ensure ultra low viscosity lubricants deliver fuel economy and wear protection it is becoming increasingly important to co-engineer the vehicle hardware and lubricant system.
Tailored lubricants
This collaborative development approach becomes even more important when you consider that not all engines deliver the
same fuel economy performance with low viscosity formulations. In recent testing Infineum examined a variety of engines using the New European Drive Cycle. The engines were run on the same SAE 0W-30 oils and measured against the same reference oil. The chart above shows the different fuel economy performance seen across the range of engines.
What is clear from our research is that fuel economy lubricants must be individually tailored to suit each vehicle type, something that will add significant complexity to their development, or compromises must be made to balance fuel economy across a range of engine types.
Viscosity and volatility Increased wear is not the only consequence of lowering lubricant viscosity because as viscosity goes down volatility also increases. In the high operating temperatures of modern engines the lighter ends of the hydrocarbons in a lubricant can evaporate. This pushes the viscosity of the lubricant up and, as a result, any fuel economy improvement gained from the low viscosity of the oil may be lost due to an increase in friction.
There is a minimum HTHS level before volatility increases above limits specified in lubricant specifications. And while using less of the additive package can improve this situation it could also compromise performance. Clearly the fine balance between viscosity and volatility is an important consideration that must be addressed in the design of innovative additive technologies, which must offer sufficient performance at lower viscosity levels.
LUBE MAGAZINE NO.128 AUGUST 2015 27
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