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Search continues for Mack T-11 engine test replacement

Work on the next heavy-duty diesel engine oil specification, dubbed “PC-12” (Proposed Category 12), is well underway. PC-12 will supersede API CK-4 and API FA-4, which were introduced in 2016. A potted history of the development of PC-12: The Truck and Engine Manufacturers Association (EMA) requested the new category from the American Petroleum Institute (API), which licences these engine oils,  in early March 2021.  Following EMA’s request, API established a New Category Evaluation Team (NCET) to assess the need for a new category. In December 2021, the API Lubricants Standards Group voted unanimously to accept the recommendation of the Diesel Engine Oil Advisory Panel (DEOAP) to proceed with establishing a New Category Development Team (NCDT) for PC-12. 

During the recent NCDT meeting held in Seattle, Washington, U.S.A. in late June, the working group outlined its progress on PC-12. The Mack T-11 engine test remains one of the major stumbling blocks. API’s Category Life Oversight Group (CLOG) confirmed in May that no existing engine tests can replace the T-11. CLOG recommended forming a Test Development Task Force to develop a replacement for the T-11. Collection of sooted oil MRV data was requested from all stakeholders on a range of engine tests including the Mack T-12A, Mack T-11A, Cummins ISM at 125 hours, Cummins ISB at 300 hours and Ford 6.7L at 175 hours.  

NCDT is working tirelessly to progress PC-12; however, the development is occurring amid a backdrop of regulatory uncertainty. The API Lubricants Standards Group has previously stressed the importance of aligning PC-12, with a first licensing no later than January 1, 2027, with the new U.S. Environmental Protection Agency (EPA) and California Air Resources Board (CARB) regulatory initiatives. 

Search continues for Mack T-11 engine test replacement

The EPA is working on several major rulemakings to revise oxides of nitrogen (NOx) emissions standards and update greenhouse gas emissions (GHG) standards for heavy-duty on-highway vehicles. The EPA regulations aim to significantly lower emissions at low speeds, idling and in stop-and-go traffic. It also proposes longer useful life periods to ensure emissions standards are achieved for more of a vehicle’s operational life. This is the first update to NOx standards in the U.S. since 2001 and will apply to Model Year (MY) 2027 vehicles. Consultation on the proposals has closed and the EPA intends to finalise the rule by the end of 2022.  

The California Air Resources Board introduced new legislation in December 2021 mandating more stringent NOx standards—starting in MY 2024 with further updates in MY 2027— targeting a 90% reduction in NOx emissions by 2031. While the rule is complete, EPA must grant a waiver before the rules can be enforced, which includes a public hearing and comment process. EPA’s virtual public hearing was held on June 29, 2022. Until the standards are finalised, category development remains somewhat in a state of flux.

A responsible, backwards compatible, soot-related viscosity test is needed for PC-12, with the Cummins ISM and Cummins ISB emerging as possible replacement options for the Mack T-11, it was heard at the meeting.

Protecting against soot-related viscosity increases continues to be an important element in heavy-duty diesel engine oil formulations. It has been apparent for some time that the T-11 is in jeopardy for PC-12 due to lack of parts to support the new category. However, developing a new engine test is costly and time-consuming and it can be difficult to exactly replace an existing engine test. The NCDT has been tasked with addressing pending test obsolescence and recommending a replacement for the Mack T-11.

The Mack T-11 is a 252-hour test using an open-chamber, in-line, six-cylinder, turbocharged, air-cooled compression ignition engine.  The T-11 evaluates soot-related viscosity increases in a turbocharged, intercooled engine equipped with exhaust gas recirculation. It is a critical test in high soot loading applications and is utilised in several heavy-duty engine oil categories including API CI-4+, CJ-4 and CK-4/FA-4.

Additive maker Lubrizol has identified a relationship between the Mack T-11 and the Cummins ISM viscosity increases, implying the potential to modify the test and resources for soot-related viscosity. If we can do this with ISM it will conserve time and resources, says John Loop, technology manager at Lubrizol who is a member of the NCDT. The standard Cummins ISM engine test is 200 hours in duration and focuses on wear and deposits. Lubrizol has been developing a 108-hour soot-viscosity flush-and-run test with no wear stage and plans to provide the data to the T-11 task force.  

Search continues for Mack T-11 engine test replacement

The Cummins ISB is a 350-hour engine test that comprises an initial 100 hours of steady state at 1,600 rpm to accumulate 3.25% soot in the lubricant, followed by 250 hours on a multi-step 28-second cycle. The Cummins ISB evaluates the ability of heavy-duty crankcase lubricants to reduce valve train wear under operating conditions designed to accelerate soot production.

Initial scoping by Southwest Research Institute (SWRI) indicates that there are more ISB engine test stands currently than ISM engine test stands, based on the Test Monitoring Center’s (TMC) Semi-Annual Report. SWRI’s early assessment highlighted ISB’s lower fuel flow rate compared to the T-11, with a reduced cost and lower carbon footprint. The power cylinders are already shown to be robust as a flush-and-run setup and it has the same targeted sooting profile as the T-11. Although, SWRI noted that EGR/Boost was not controlled for this scoping run. SWRI’s analysis has been shared with Cummins and CLOG in preparation for industry efforts to develop a replacement for the T-11.

Data from the American Chemistry Council (ACC) – Petroleum Additives Panel has raised some concerns that the Cummins ISB and ISM do not generate enough viscosity increase to replace the Mack T-11. Results from 17 Cummins ISB candidate oil tests demonstrated soot loading between 4.4% and 7.4% soot, with the highest viscosity growth of <5 centistokes (cSt). 54 Mack T-11 candidate test results show that at soot loading of 5.9-6.5% only 30% of oils had viscosity growth of less than 5 cSt. ISM recorded soot loading of between 5.8-8.4% soot in 46 candidate test results. In 87% of the candidate test results, the highest viscosity growth was <4.5 cSt.

Redundancy of the CAT 1N engine test is also under investigation. The CAT 1N evaluates the performance of a crankcase lubricant for piston deposits, ring sticking, piston scuffing, ring scuffing, liner scuffing and lubricant consumption. Caterpillar is reviewing possibly retiring the 1N, but no current conclusion has been reached, says Hind Abi-Akar, lubricants and fuels technical expert at Caterpillar. Nevertheless, testing on 21 candidate pairs from the CAT C13 and CAT 1N has indicated that the CAT 13 is a “promising” replacement.  In 81% of tests, candidate oils either passed or failed both tests. Two out of 21 passed the CAT C13 and failed the CAT 1N, which is of some concern. During the Seattle meeting, details of other key test changes were discussed including the addition of the Ford 6.7L Valve Train Wear (VTW) engine test for soot valve train wear (abrasive and rolling) and a new DD13 Piston/Liner Scuffing Wear (Adhesive) engine test. The final tests to be included in PC-12 have not yet been decided. Once confirmed, the Matrix Design Task Force will develop the appropriate matrices for Precision/Base Oil Interchange (BOI)/Viscosity Grade Read Across (VGRA) and allow the PC-12 Funding Task Force to propose matrix designs that fall within available funding means. A final determination for inclusion and limits will be voted on based on matrix outcomes and technical demonstration.