The challenge of low-viscosity engine oils
R. David Whitby | TLT Worldwide May 2016
A project is planned to demonstrate a concept car with a lower viscosity grade by mid-2016.
The development of even lower viscosity engine oils has been a goal of car and van manufacturers in North America, Europe and Japan for some time.
© Can Stock Photo Inc. / romarti
IN APRIL 2013 THE SOCIETY OF AUTOMOTIVE ENGINEERS (SAE) Engine Oil Viscosity Classification J300, which provides the kinematic and dynamic viscosity limits for automotive engine and gear oils (such as 5W-30, 10W-40 and 20W-50), was revised again to include a lower-viscosity engine oil grade, 0W-16. The classification was revised again in January 2015 to include two further lower viscosity engine oil grades: 0W-12 and 0W-8.
All three viscosity grades were established “to provide a framework for formulating lower high-temperature high-shear viscosity engine oils in support of the ongoing quest of engine builders to improve fuel economy.” Better fuel efficiency can be helped by reducing hydrodynamic friction between moving parts, such as piston rings, bearings and valve trains.
For several years, Honda has successfully lubricated a number of ultra-fuel-efficient passenger car models with a Honda-approved engine oil that has the properties of a 0W-8 viscosity grade. Honda was able to give the SAE task force, responsible for engine oil viscosity classification, the technical data to support the new viscosity grades’ definitions. Honda disclosed plans in January 2015 to further apply and expand the application of 0W-8 engine oils in Japan. The company does not have immediate plans to introduce 0W-8 or 0W-12 viscosity engine oils in North America or Europe but is currently focused on how 0W-16 viscosity engine oils can be applied to Honda passenger car models in North America.
The development of even lower-viscosity engine oils has been a goal of car and van manufacturers in North America, Europe and Japan for some time. Honda presented data to the ICIS Asian Base Oils and Lubricants Conference in 2011, which showed that future engine oils designed for automotive fuel economy improvement would require new viscosity classifications below the then lowest viscosity of 0W-20.
In November 2015 Shell, Gordon Murray Design (GMD) and Geo Technology announced a project that plans to demonstrate a concept car by mid-2016 that will have a fuel economy of 100 miles per gallon and use a 0W-12 viscosity engine oil. Shell has found that transportation (cars, vans, trucks, buses, motorcycles, trains, ships and planes) accounts for 35% of worldwide energy use. Gordon Murray Design’s founder, Gordon Murray, designed Formula 1 racing cars and designed the McLaren F1 road car.
However, there are several technical hurdles that need to be overcome before these ultra-low viscosity engine oils can be used more widely.
Lubrizol has noted that lower viscosity can have a negative impact on durability. The protective oil film is less robust and, under the most extreme loading conditions, may be non-existent. As a result, Lubrizol has already begun product development on a specially formulated additive to meet ultra-low viscosity durability requirements. Other goals will be to provide improved high temperature deposit protection for pistons, better sludge control and seal compatibility.
The Shell/GMD project is working on specially tailored material coatings for piston rings and cylinders the enable engines to function with ultra-low viscosity engine oils. The special coatings include diamond-like materials, titanium and other materials. The project also is researching how to apply these coatings, recognizing that it always depends on operating conditions such as friction and pressure.
Shock loads on bearings also might need to be reduced severely or eliminated altogether. Bearings could require special coatings. This might mean engines will need to be run under constant operating conditions such as in hybrid electric vehicles in which the engine is simply being used to run a generator to charge the batteries, which actually drive the car.
Additionally, it could be very difficult to formulate ultra-low viscosity engine oils using Group II base oils. Infineum has observed that ultra-low viscosity oils are likely to need Group III, Group III+, polyalphaolefins (PAOs) and/or esters, or combinations of some or all of these base oils. The additive manufacturer recognizes that this is a complex area, driven mainly by OEM specifications, so that the mix of Group III, III+, PAOs and esters could vary depending on the most challenging characteristics of the specification.
It looks as though the next few years are going to be very challenging for OEMs, additive manufacturers and base oil suppliers as they develop, test and introduce ultra-low viscosity engine oils.
David Whitby is chief executive of Pathmaster Marketing Ltd. in Surrey, England. You can contact him at pathmaster.marketing@yahoo.co.uk.