Increased focus on biodiesel cleanliness and compatibility
In both ACEA E8 and ACEA E11, the OM646LA Bio-Diesel Engine Test (CEC L-104-16) limits for piston cleanliness are increased compared to prior sequences ACEA E6 and ACEA E9. This increase in severity is an important update which further addresses lubricating oil degradation due to FAME (Fatty Acid Methyl Ester) content in modern diesel fuels. Biodiesel (FAME) can disproportionately accumulate in the sump during engine operation due to its lower volatility profile versus typical mineral diesel. The reactivity of FAME can increase the rate of lubricant oxidation and degradation, which can increase the formation of performance-draining piston deposits.
Delivering improved cleanliness and wear protection
Another critical element of the ACEA 2022 heavy-duty update is further alignment with industry-recognised API engine tests for improved engine cleanliness and wear protection. In ACEA E7 and ACEA E11 we see the introduction of the Caterpillar 1N (ASTM D6750) and Caterpillar C13 (ASTM D7549) cleanliness tests respectively. Whilst the option remains to use the Daimler OM501LA (CEC L-101-09) data to support ACEA E7 and ACEA E11 (to ACEA E9 limits), the inclusion of the Caterpillar tests ensure cleanliness remains a key, measured parameter as the Daimler OM501LA hardware availability reduces over time. In the ACEA E4 and ACEA E8 categories, a new industry engine test has been introduced; the Daimler OM471 piston cleanliness test (CEC L-118-21) and is a replacement for the Daimler OM501LA. While the Daimler OM471 piston cleanliness test is mandatory in the new ACEA E8 category, OM501LA test results meeting the requirements of ACEA E4-16 may still be utilised for the latest ACEA E4 category.
Developed by Daimler, the OM471 six-cylinder engine test is designed to assess the performance of lubricating oils against piston deposits. A critical aspect of the Daimler OM471 engine is the use of steel pistons versus conventional aluminium pistons used in the Daimler OM501LA test.
Aluminium pistons have shown strong performance characteristics historically. However, steel pistons present advantages in the forms of improved fuel economy performance (due to less friction), high torque management, long durability and improved
total cost of ownership. The move from aluminium to steel hardware metallurgy is significant and presents new lubricant performance challenges.
Major lubrication implications ACEA E8 | new category ACEA E8 is a forward-looking category and should not be regarded as a simple category replacement for ACEA E6. Rather, it should be viewed as a performance increase and the most significant aspect of the ACEA 2022 update. ACEA E8 aligns with the latest generation commercial vehicle hardware in the market, and enables OEMs to specify a lubricant at a new performance level and will require even more stringent testing to carry the latest ACEA claims.
The new Daimler OM471 piston cleanliness test The introduction of the Daimler OM471 piston cleanliness test perfectly encapsulates the ACEA E8 implications for lubricant marketers. The Daimler OM471 test, which uses steel pistons, runs at higher temperatures and is double the duration of its predecessor (Daimler OM501LA), ensuring heavy-duty commercial vehicle engine oils meet new cleanliness requirements. The transition from the use of aluminium to steel pistons within commercial vehicle engines has been a trend since the 2014 introduction of Euro VI. OEMs have been challenged with the need to further optimise combustion efficiency, driving an increase in cylinder pressures and combustion temperatures. Aluminium pistons, which historically displayed excellent performance characteristics, could no longer deliver durability at the increased pressures and heat cycling, hence the increased use of steel pistons. The latest designs of steel pistons include large volume cooling chambers in close proximity to the piston crown and ring grooves which are pressure fed with the engine lubricant to provide piston cooling and prevent excessive pistons crown temperatures.
Steel pistons are designed to maximise the cooling through use of chambers and thin walls (reference Figure 2). Lubricant is sprayed at the undercrown of the piston and acts as a thermal transfer fluid. In extreme operating conditions, the lubricant in these regions must cope with temperatures in excess of 350°C, therefore a lubricant with high levels of oxidative stability is required. Lubricants which cannot cope with these temperatures can lead to
Continued on page 12 LUBE MAGAZINE NO.170 AUGUST 2022 11
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