The long road to cleaner air and lower-ash lubricants

In the past two decades, landmark legislation on air quality has had a far-reaching impact in diesel engine design and maintenance. Specifically, the EPA 2010 emission rules governing on-highway vehicles and Tier 4 Final rules for off-highway equipment mandated sharp emission restrictions on nitrogen oxides (NOx), particulate matter (e.g. soot) and carbon dioxide (CO²). Meeting these standards has required a well-coordinated effort among engine manufacturers, fleet operators, energy companies and lubrication producers like Chevron. It has entailed tradeoffs that have bottom-line implications. And although we have made great strides in reducing harmful emissions from diesel-powered vehicles, changes in engine design and exhaust after-treatment systems have placed an increased burden on maintenance teams to learn how to properly care for the new equipment.

To meet these stricter standards, OEMs focused primarily on adjustments to the hardware – the engine technology – with an emphasis on exhaust aftertreatment systems, or EATS. The evolution began with the introduction of exhaust gas recirculation (EGR) systems, which return exhaust to engines to be further combusted. The evolution continued with the addition of EATS, diesel particulate filters (DPF) and selective catalytic reduction (SCR). Implementation of off-highway standards proceeded at a slower pace, but on a parallel track with similar types of technologies. Today, virtually all OEM’s have incorporated a combination of EGR, DPF and SCR systems into their designs.

Of course, those of us in the lubricant business have had to evolve as well to keep up with the changes in engine design and the evolution of aftertreatment systems. The combined demand for fuel efficiency and more effective emission control has been the chief driver of changes in engine oil technology and API specifications over the past decade. A particular challenge has been ensuring that lubricants don’t hinder the performance of EATS. Diesel particulate filters are designed to capture soot particles and prevent them from escaping into the air, but they also capture non-combustible ash produced by metallic additives in engine oils that are intended to protect the engine. The API CK-4 engine oils specification, released commercially in late 2016, limits the amount of metallic additives that can be used in an oil in order to reduce the risk that they will interfere with DPF operation. The percentage of ash forming metallic additives in oils has been limited to 1% since the introduction of API CJ-4 specs in 2006.

There is little question that changes in engine design and aftertreatment systems have had a beneficial effect on the air we breathe and reduced the on- and off-highway industries’ emission footprint. The increased maintenance burden on fleets, however, has proved costly. And the ash forming metallic additive content of oil can be a complicating factor in EATS maintenance. In our next blog, will explore the impact of these changes on fleet operators from a maintenance and cost perspective.