The American Petroleum Institute’s (API) Proposed Category 12 (PC-12) is currently under development. A target first license date has been set for January 2027, and industry stakeholders are currently at work on PC-12’s testing requirements, limits and other criteria that will make up the final performance category. That means change is coming to the heavy-duty diesel lubricants space.
The introduction of a new category provides opportunities for enhanced lubricant performance in areas such as improved drain intervals, fuel economy and engine deposit protection. However, one major area of focus for next-generation lubricants will be greater protection and enablement of aftertreatment devices, helping heavy-duty OEMs comply with stringent new emissions standards set by the U.S. Environmental Protection Agency in 2022.
Those standards are scheduled to go into effect for model year 2027 diesel engines – hence the new category’s timeline – and they represent a true step change, including:
- A 75% reduction in nitrous oxide (NOx) emissions
- A 50% reduction in particulate matter (PM)
- Extended service life for aftertreatment devices, growing from about 435,000 miles (700,000 km) to 800,000 miles (1.29 million km).
Indeed, aftertreatment devices are an increasingly important part of how heavy-duty diesel vehicles will continue to meet lower and lower emissions standards. For that reason, tomorrow’s engine oils must be formulated with the needs of such devices in mind.
One challenge for the new category is accommodating the diverse range and needs of all heavy-duty equipment, including off-highway machinery, which differs from on-road vehicles in terms of duty cycles and wear protection requirements. As a result, formulators are focused on delivering equal or superior performance across all applications while controlling costs and avoiding over-formulation.
What’s in the box?
As part of PC-12’s development, significant changes are coming to the category’s “chemical box,” or the acceptable limits and proportions of chemistry that go into a final PC-12-compliant formulation.
One chemical in particular has been targeted: phosphorus, which has historically been deployed for its anti-wear properties. Specifically, zinc dialkyldithiophosphate (ZDDP) has been a widely used anti-wear additive for finished lubricant formulations. ZDDPs also inhibit oxidation and deposit formation within the lubricant formulation. Phosphorus levels in PC-12 fluids will be limited to 800 parts per million (ppm), a 30% reduction from the 1,200 ppm figure allowable in current bottles of oil.
Highly efficient exhaust gas aftertreatment equipment allows trucks to meet EPA and CARB emission criteria. Importantly, the selective catalytic reduction (SCR) system reduces NOx levels in exhaust gases through the action of a metal catalyst in conjunction with diesel exhaust fluid to produce benign byproducts. However, during engine operation, phosphorus in the lubricant can enter the exhaust and react with the SCR’s catalyst, reducing its activity. This leads to a drop in the effectiveness of the system to reduce emissions and shortens the lifespan of aftertreatment devices. As a result, PC-12 with a reduced phosphorus content was introduced to protect the equipment.
While current phosphorus levels have been acceptable over the course of a 400,000-mile (645,000-km) service life, new EPA requirements double that figure. Low-phosphorus formulations are therefore required to prolong the functionality of the aftertreatment device. Low-phosphorus formulations are available today and have been formulated with both on- and off-highway needs in mind. However, they are not part of the current performance category, and this marks a noteworthy change from today’s widely available engine oil formulations.
Delivering adequate wear protection
Low-phosphorus engine oil formulations for heavy-duty diesel use are not entirely new. Comparable lubricants have already been used throughout Europe and in some applications in the North American market.
However, concern has been raised during the development of PC-12 regarding off-highway applications – construction equipment, mining trucks, agricultural machinery and more – which commonly use the same API-certified lubricants as on-highway trucks. Within these applications, duty cycles differ substantially and can be more severe than on-road trucks. Additionally, wear protection is critical to provide off-highway engine longevity, reduce engine rebuild costs and limit equipment downtime.
Mining equipment provides an instructive example, which operates at or near full load for extended periods, often under extreme conditions. This equipment also generates higher torque output at lower speeds, which can place excessive stress on engine components. Operational severity in new-model equipment will likely continue to increase as OEMs look for further efficiency gains.
How low-phosphorus formulations can deliver protection
The need for excellent wear protection throughout all heavy-duty applications has led formulators throughout the industry to be proactive in investigating alternative formulations with new chemistries that can stand up to the demands of off-highway equipment. Balancing this need with enabling on-road trucks and aftertreatment devices is critical. PC-12 will demand it.
Replacing ZDDPs requires performance considerations across three key areas:
- Anti-wear protection
- Oxidation performance
- Deposit formation.
Various alternative anti-wear chemistries and film-forming polymers have demonstrated that efficacy across each performance area will require more than a simple one-to-one replacement. Instead, it will require a combination of several additive chemistries – but OEMs and end users can rest assured that effective formulations will be available despite the new chemical box restrictions.
To demonstrate the efficacy of these next-generation lubricants, additive suppliers, including Lubrizol, are utilizing field trials to demonstrate the robustness of their formulations’ anti-wear, oxidation- and deposit-resisting performance. Additionally, many products that exist in the market today with reduced phosphorus levels have shown excellent performance over many millions of miles, paving the way for this new generation of engine oils.
Greater value, collective success
There is significant work to do as the lubricants industry prepares for PC-12’s first license. OEMs, oil marketers and additives suppliers continue to work in close concert to ensure that end users can depend on reliable, effective solutions that can enable heavy-duty equipment of all types to perform as intended. End users will likely find it worthwhile to consult with their lubricants suppliers early and often about PC-12-compliant fluids. Early collaboration, testing and on-road use are critical for developing reliable new fluids.
The resulting technologies will deliver greater efficiency for operators, including greater fuel efficiency, long-lasting aftertreatment device efficacy and reliable protection that heavy-duty fluids have delivered throughout their history. And it means significant benefits for everyone.
Zachary L. Rodgers is the Engine Oil Development Manager at Lubrizol Additives, where he leads formulation strategies for heavy-duty engine oils. He wrote this article for SAE Media.
