Courtesy of Engine Technology International
Increased fuel economy and reduced greenhouse gases are being supported by lower ‘high-temperature high-shear’ engine oil viscosity
The continuing environmental drivers and legislation for reduced emissions and increased fuel economy continues to force changes in engine hardware design around the world. Significant changes in heavy-duty diesel engine technology and operating conditions have resulted in engine downsizing, down-speeding, higher oil temperatures, stop/start technology, and variable valve timing, to name a few. At the same time, advances in heavy-duty diesel engine oils have played a vital role in enabling these performance improvements.
Using lower viscosity grades – moving from traditional 15W-40 to 10W and 5W viscosity grades – is now well accepted as delivering increased fuel economy and reduced greenhouse gases (GHG). At the same time, demonstration that hardware protection is not sacrificed is proven by stringent testing alongside millions of miles of real-world driving.
The viscosity of an oil is measured by kinematic viscosity (KV) – the time that is measured for a fixed volume of liquid to flow through a tube under the force of gravity. However, in an operating engine, oil is exposed to more than just gravity, notably nowadays where it has to run in hotter and more severe operating conditions.
High-temperature high-shear (HTHS) is the current industry standard test that best predicts fluid behavior in these more representative operating conditions. Within an engine, HTHS is relevant across the bearings, camshaft, and piston and liner areas. As with KV, HTHS is not new – with limits being explicitly defined within SAE J300 as far back as the early 1990s.
HTHS is designed to ensure that oils do not shear down at high temperatures and shear rates, which ensures that film strength remains acceptable for component longevity with thinner oils, and delivers even further fuel economy and reduced GHG.
Lower HTHS is actively being pursued by an increasing number of heavy-duty OEMs (including FPT Industrial and Scania), to move significantly below the long-established 3.5cP HTHS limit in conjunction with modern engine hardware designs.
Industry specifications are also being rolled out to reflect the needs from engine manufacturers. The American Petroleum Institute (API) will see the introduction of its first-ever split category of API CK-4 and API FA-4 in December 2016. While API CK-4 will offer backward compatibility (minimum 3.5cP), API FA-4 will offer fuel economy benefits through lower HTHS between 3.2 and 2.9cP. The European Automobile Manufacturers’ Association (ACEA) is likely to follow with a new sequence at 2.9cP HTHS in the next upgrade after ACEA 2016.
The focus on lower HTHS is gaining momentum as it is regarded as the latest view that more accurately mimics the engine oil behavior in the increasingly severe operating conditions. “Such a move to lower HTHS engine oils is complex,” says Keith Corkwell, global business manager for Lubrizol’s heavy-duty diesel engine additives segment. “The vital roles of the additive package, performance polymer and the base oil need to work in harmony with the changes in engine hardware. Lubrizol backs this up with its extensive research, development and millions of miles of field testing in order to demonstrate proof of performance in real-world driving conditions.”
Lubrizol’s proven range of performance additives and polymer technologies can be tailored to meet the individual OEM’s specifications, designs and materials. All of these lower HTHS requirements can be met when the engine oil is included as an integral part of the design process, with all partners working in a close and cooperative environment to meet the same goal.