Global governmental vehicle regulations call for improved fuel efficiency and reduced greenhouse gas (GHG) emissions. One of the ways to achieve these is through the use of lower high temperature high shear (HTHS) viscosity. A measure of a fluid's resistance to flow. A fluid with a higher viscosity flows less easily. engine lubricants, alongside more modern engine design.
In this video, we look at the impact of HTHS viscosity on the following:
- API CK-4, API FA-4 and MB 228.61 specifications
- Fuel savings
- Testing procedures
Global governmental vehicle regulations call for improved fuel efficiency and reduced greenhouse gas emissions. One of the ways this can be enabled is through the use of lower high temperature high shear viscosity engine (HTHS) lubricants alongside more modern engine design and technologies.
HTHS measures the viscosity (resistance to flow) of an engine lubricant at elevated temperatures under constant shear, simulating the narrow tolerances and high speeds between moving parts in a hot engine. The lower the measured torque, the lower the measured HTHS viscosity of the oil, and in turn, the greater the increase in predicted fuel efficiency.
Traditionally, heavy duty diesel engine lubricants have had a minimum HTHS viscosity rate of 3.5 millipascal per second, commonly referred to as 'centipoise' (cP).
In the United States, the American Petroleum Institute (API) has, for the first time ever, split the category for heavy duty engine lubricants into two. The API CJ-4 category has been superseded by API CK-4, driven by new technology and verified, stringent testing. API CK-4 requires a minimum HTHS viscosity of 3.5 cP. The new category API FA-4 requires all the performance requirements of API CK-4, with the addition that the oils are blended with a HTHS viscosity range of between 2.9 and 3.2 cP.
In Europe, Mercedes-Benz was the first European OEM to introduce a service fill low HTHS engine lubricant specification, known as MB 228.61
Two ACEA fuel economy categories are being proposed to deliver fuel efficiency benefits whilst ensuring engine protection is not compromised. These will be introduced in a future ACEA specification upgrade, expected to be mid-2020.
Long haul heavy duty commercial vehicles can realistically expect fuel savings of 0.5-1.5% by switching from SAE 15W-40 to 5W-30 HTHS engine lubricant. Further savings when switching to low HTHS viscosity engine lubricant can be expected to add 0.4-0.7% of increased fuel efficiency, depending on the engine type and operating conditions.
One method to measure HTHS viscosity is the tapered bearing simulator. In this test method, engine lubricant is injected through between a tapered rotor and stator which is run at 150° Celsius and measures the oil's resistance.
The move to lower HTHS viscosity engine lubricants requires design, development, and formulation changes, where performance additives and performance polymers have a key and fundamental role.