The classes are divided into categories to meet the requirements of different engines. For example, in the heavy-duty engine oil sequences, ACEA E4 is suitable for engines meeting Euro I, Euro II, Euro III, Euro IV and Euro V emission requirements, compared with ACEA E8, which meets Euro VI emission standards. Euro VI reduced the limit for NOx to around 0.46g/kwh from 2.0g/kwh in Euro V.

Each new issue of the sequences also takes into account the latest developments in engine and lubricant technology. With engine technology changing at an ever-increasing rate, why the gap from 2016 to 2022?

The 2016 light-duty sequences underwent several revisions in the intervening period. Updates were made to some of the tests, including the introduction of the M271Evo (CEC L-107-19) sludge test as an alternative to the Daimler M271. But the amount of change in the industry meant unprecedented levels of change to the sequences were required. Agreement had to be reached on new categories and new engine tests. There also had to be consensus on tests to replace those that were coming to the end of their life.

In May 2021, ACEA reached an agreement and the 2021 light-duty sequences were published. This was a significant step, publishing new sequences for light-duty vehicles only. Historically, every publication of new sequences had been simultaneous, with both light-duty and heavy-duty sequences published at once. 

For the heavy-duty sequences, there was a much longer wait. As Infineum Insight reported in April 2021, there was still much to be resolved.

“The OM471 must become a CEC test; appropriate limits have to be defined for ACEA E8/F8 and ACEA E4,” an article in Infineum Insight said. “An industry effort to gather OM471 candidate results to support data-based limit setting was not successful. One can imagine that there are not very many results available in the industry given the newness of the test and the cost involved in running a 600-hour heavy-duty engine test. However, having OM471 candidate data is just one part of the equation. Limits cannot be set by looking at one test in isolation; compatibility with other sequence requirements has to be checked, notable with the newly introduced performance requirements.”

After further development work, a 2022 edition of the ACEA Oil Sequences for Heavy-Duty Engines was published in May, and the industry has clarity for the road ahead. The new sequences address engine developments that are driven by a combination of regulatory and performance needs, complemented by necessary test maintenance requirements. 

Two entirely new categories, ACEA E8 and ACEA E11, have been introduced to replace the obsolete ACEA E6 and ACEA E9 categories. 

The ACEA E8 category is for highly rated diesel engines that meet Euro VI and earlier emissions requirements and are operating under very severe conditions, including significantly extended oil drain intervals. It is suitable for EGR engines, with or without particulate filters, and for engines fitted with SCR NOx reduction systems. ACEA E8 quality oil is strongly recommended for engines fitted with particulate filters and is designed for use in combination with low-sulfur diesel fuel. 

Validation of Old and New Editions of ACEA Heavy-duty 

ACEA E11 is recommended for highly rated diesel engines meeting Euro VI and earlier emissions requirements, running under less severe conditions than the ACEA E8 category. Like ACEA E8, it is suitable for engines with or without particulate filters, for most EGR engines and for most engines fitted with SCR NOx reduction systems. ACEA E11 is strongly recommended for engines fitted with particulate filters and is designed for use in combination with low-sulfur diesel fuel. 

The Volvo T-13 test has been adopted into both ACEA E8 and ACEA E11 to achieve a significant boost in oxidation control. Another test, the Caterpillar Oil Aeration Test, has also been included to improve aeration control.

The ACEA E4 and ACEA E7 categories have been updated with new piston deposit tests, replacing OM501LA. Both categories are intended for older engines complying with Euro V or earlier emissions standards. These engines may be equipped with SCR or EGR but not particulate filters. ACEA E4 is most suitable for very severe operating conditions with significantly extended oil drain intervals, whereas ACEA E7 is suitable for less severe operating conditions. 

The OM501LA test was the main piston cleanliness test in the ACEA heavy-duty sequences, but with hardware out of production and the remaining stocks having run out, it needed to be replaced. The OM471 test was selected as a replacement for ACEA E4 and ACEA E8. The OM471 was a proprietary test developed by Daimler and has been successfully adopted as a CEC test procedure. The hardware better represents current engine technology, including such features as steel pistons, common-rail injection system, asymmetric exhaust gas turbocharger and Euro VI-compliant emission control based on selective catalytic reduction technology, exhaust gas recirculation and particulate filter. The test is twice as long as the OM501LA (CEC L-101-08) test at 600 hours.

The ACEA 2022 sequence update raises antioxidation performance and piston deposit control, with pass levels for the new OM471 test in ACEA E4 and ACEA E8 more severe than those previously set. 

“The new OM471 engine tests set a new industry standard in terms of engine test severity and test duration of one month,” said Paul van de Heijning, co-chairman of the Industry Liaison Committee for the Technical Association of the European Lubricants Industry. “This increased piston cleanliness performance is needed to cope with the significantly higher operating temperatures of the latest Euro VI HD engines using SCR systems, driven by Euro VI [nitrous oxide] emission legislation in combination with extended oil drain intervals.”

The OM501LA has also been replaced in both the ACEA E7 and ACEA E11 categories. While the OM501LA data can still be used to support these claims, we see the introduction of the Caterpillar 1N single cylinder engine test in ACEA E7 and the introduction of the Caterpillar C13 engine test in ACEA E11.

The light-duty sequences introduced new engine tests to take account of the need for lower-viscosity fluids, but viscosity has not been specifically addressed in these heavy-duty sequences. There was a desire to introduce new F-categories with lower viscosities—ACEA F8 and ACEA F11—with two new low-soot wear tests being developed to become part of those new categories. However, the test development has been unsuccessful. Despite significant efforts, both test development groups could not confirm wear issues with lubricants in this viscosity window, as no meaningful difference in performance could be found between lubricants. ACEA is planning to continue work on the test development and it may be part of the next revision, as heavy-duty vehicles look to follow light-duty vehicles by reducing viscosity to achieve increased fuel economy.

Claims can already be made against the 2022 ACEA Oil Sequences for Heavy-Duty Engines as of May 1. It will become mandatory for all new claims made from May 1, 2023, onward. Products conforming to the ACEA 2016 E sequences can be marketed until May 2024.

Governments around the world have made their emissions agenda clear. Original equipment manufacturers are developing new engine powertrain systems for heavy-duty vehicles that continue to improve fuel efficiency and deliver the higher performance expected from customers while also meeting the latest stringent emission requirements. This includes exploring electric-, hydrogen-fuel-cell- and gas-powered solutions, as well as even more efficient gasoline and diesel options. 

Lubricants are adapting to meet these new challenges and provide the lubrication required in these high-stress conditions, providing uncompromised engine protection over longer drain intervals. For example, OEM requirements for lubricants to deliver fuel economy via reduced frictional losses has led to a general reduction in the viscosity of heavy-duty engine oils. But careful evaluation of lubricant shear stability is essential to ensure lower-viscosity oils offer sufficient protection to heavy-duty diesel engines. Viscosity modifiers with a chemistry and architecture that can deliver good shear stability while providing a high contribution to kinematic viscosity will be essential as lubricants are formulated to deliver excellent wear protection and fuel efficiency.

The sequences provide for a modernization of the requirements for heavy-duty engines and corresponding engine oil specifications that bring them up to date in the market. They recognize engine developments in this critical area and align the automotive requirements with the latest heavy-duty engine emission standards. Products conforming to the new specifications will provide performance benefits to operators of heavy-duty commercial vehicles. 

But all this change to engine and lubricant technology is happening on the back of a shifting vehicle parc. While fleet operators are under pressure to adopt lower-emission technologies, the vehicle parc itself is aging as motorists and haulers hold on to their vehicles for longer than ever.

Trucks are on average 13.9 years old in the European Union, up from 12.4 years in 2019, according to the ACEA Vehicles in Use Report 2022. Buses on EU roads are on average 12.8 years old, up from 11.4 years in 2019. Despite increased registrations in recent years, alternatively powered vehicles remain only a small part of the market.

Lubricant blenders and manufacturers must find the balance between supporting developments in technology and meeting climate objectives while providing the existing vehicle parc with suitable lubricants.  

Mike Bewsey is chairman of the Verification of Lubricant Specifications and business unit director of Moove Lubricants. Bewsey has been involved in VLS since 2016 as a board member and was appointed chairman in 2021.