Maintenance issues in aftertreatment systems: The causes and the costs

Are exhaust aftertreatment systems (EATS) giving your maintenance crew a hard time? Are you finding that diesel particulate filters (DPFs) have to be serviced more often than OEM guidelines suggest? If so, you are not alone.

In an earlier Lube Matters article, we looked at the evolution of EATS over time in response to government mandates around the world to reduce emissions from diesel engines. With all the major truck and heavy-duty equipment manufacturers incorporating DPFs in their engine designs, carbon emissions have fallen dramatically over the last decade, while fuel efficiency has increased. But these systems have added costs for fleet operators, both in acquisition and in ongoing maintenance. Modern aftertreatment systems add significantly to the cost of new trucks and off-highway equipment, with some systems adding as much cost as the engine. Once new equipment has been placed in service, operators find they have to clean DPFs frequently through an expensive regeneration process. Units that have become excessively clogged are prone to cracking and their service life is often shorter than expected. Replacement units can range between $3,000 and $7,000. Besides the direct costs of repairing or even replacing DPFs, these issues further generate indirect costs of labor productivity, downtime and under-utilization of equipment. A DPF replacement will likely take a vehicle out of service at least one or two full days.  

These problems are not inherent to DPFs or their design, nor should OEM guidelines be faulted. Engine lubricants contain metallic additive materials that help protect metal surfaces in the engine, but they also form non-combustible ash in the exhaust, which clogs up emission control filters. In fact, as much as 98% of non-combustible matter in a typical DPF are the result of lubricant additive materials and soot. Detergents containing calcium or magnesium, and anti-wear additives containing zinc, contribute significantly to ash accumulation.

Oil specifications have changed over time to keep up with lower emission demands, but have not specifically addressed EATS. The maximum ash content allowed in diesel engine lubricants has remained at 1% under the API CK-4 standard, introduced in 2016. But not all CK-4 oils are formulated the same. Certain types or higher amounts of metallic additives will result in faster rates of ash accumulation. Engine load can also be a factor – the more stress an engine is under, the more ash is likely to accumulate.

Even with modern lubrication advances, DPF maintenance, repair and replacement costs related to ash accumulation continue to burden many equipment managers. The question for lubrication producers is whether they are up to the challenge of reducing ash content while simultaneously delivering the protective benefits equipment operators demand. Not only is it a maintenance issue, but non-combustible ash in a DPF is also a drag on fuel economy. That’s a whole other topic in itself, which we will tackle in our next article.