The future of lower viscosity oils
Producing lower viscosity grades has become a key target for lubricant manufacturers the world over in recent years.
With the impending changes to carbon dioxide emission regulations being introduced as soon as 2020, the emphasis is now increasingly being placed on the manufacturing of thinner oils.
Maximising fuel economy benefits is the principle driver behind these changes but an important balance has to be struck to ensure wear protection isn’t compromised, thus affecting the performance of the entire engine.
Maintaining the barrier for protection via an oil film through moving parts is crucial and to ensure that is achieved, the High Temperature High Shear Viscosity Test has become an increasingly significant tool. Carried out at 150 degrees centigrade, the conditions of this test replicate exactly what would happen in an engine.
Andy Brown, UK Automotive Technical Manager at FUCHS Lubricants, the independent lubricant manufacturer, said: “HTHS viscosity is becoming increasingly important and that trend will only continue.
“Due to the fact that the test is carried out at 150 degrees centigrade, it gives a better idea of the effect that will have on the fuel economy.
“HTHS is also becoming a bigger part of the manufacturer’s requirements these days. The HTHS viscosity will become a massive focus for manufacturers because the oil has to have the correct viscosity at that temperature so the engine can meet its fuel economy targets.
“That isn’t easy to do. When you start getting extremely low in terms of viscosity grades, you are looking at a shift in additive technology as well. It certainly won’t be the same sort of additives we use today so that is another factor which has to be taken into consideration.
“At FUCHS we have a significant number of OEM approvals which we are required to meet and this HTHS viscosity test is becoming an important part of obtaining them.
“It is time consuming and expensive but it does give confidence that our products stand up to scrutiny and offers assurances about fuel economy and emission limits.”
The principles behind lubrication offer a clear reasoning for why viscosity levels are so critical to fuel efficiency, in particular those which underpin hydrodynamic lubrication and boundary lubrication.
Hydrodynamic lubrication exists when moving component surfaces are separated by a continuous unbroken oil film, with the load taken completely by the oil film.
In contrast, boundary lubrication exists when operating conditions dictate that it is not possible to establish a full fluid film, particularly at low relative sliding speeds. The oil film thickness is such that metal-to-metal contact can occur.
While hydrodynamic lubrication provides a vital and important protective film, it also introduces issues such as viscous drag and pumping losses that actually cause internal energy losses. The thicker the oil is, the greater the frictional losses and so the greater the impact on fuel efficiency and economy.
As a result, the Society of Automotive Engineers (SAE) in recent years have introduced viscosity grades of 16, 12 and 8 in what has been the first changes to the J300 classifications in more than a decade.
Lower viscosity grades will introduce their own issues and improved additive technology and performance will be required to provide greater wear protection and friction control under severe operating conditions.
Andy added: “With lower viscosity grades the balance between film thickness and internal frictional losses mean that boundary lubrication is likely to occur more often. Where the oil film thickness is already right on the limit compared to the surface finish, add in higher combustion pressures and loads and it is almost inevitable that metal to metal contact will occur.
Lower viscosity grades are therefore likely to herald a big increase in additive performance, friction modification and possibly a complete re-think on how to control wear in these boundary regions. There will be some serious additive development going on in the coming months and years.
“Overall though, the shift to lower viscosity grade is an essential one to meet the fuel economy targets. SAE 0W-16 already exists in some markets and here at FUCHS we fully expect to see xW-12 in the near future.
“As for xW-8, it’s just a case of watching this space. It will come – it’s just a matter of when rather than if.”
LINK
www.fuchs.com/uk
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LUBE MAGAZINE NO.134 AUGUST 2016
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