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Over the last decades, heavy duty diesel engines have experienced many changes in design and operation. More stringent emission legislation has been a driver for changes in the design of heavy duty diesel engines since the 1980s. Optimization of the combustion process and the introduction of exhaust gas recirculation allowed for significant reductions of exhaust emission levels over the years, but the thermal loading of the engine and its lubricant has increased. In the coming years, diesel engines will have to meet even more stringent requirements for particulate matter and nitrogen oxide emissions. These low emission diesel engines are expected to be equipped with exhaust gas after-treatment systems.

Emission legislation for diesel engines is becoming more stringent over time. While the exhaust gas composition requirements for prior iterations of emission legislation could be met with improvements in the engine's combustion process, the next issue of emission limits may require more rigorous measures. In order to meet severe particulate matter limitations, such as those mandated in Japan's new long-term (2005-) emission regulation and in Euro-4 emission legislation, the use of exhaust gas after-treatment systems seems unavoidable. Many engine builders seem to have selected the Diesel Particulate Filter (DPF) as an integral part of their selected after-treatment strategy. It has been stated that engine lubricants may hurt the durability of such after-treatment systems when oil consumption results in deposit build-up on the DPF walls. This paper describes how a study was performed on the possible impact of engine lubricant composition on DPF plugging.

Historically, the characterization of fresh and used diesel engine lubricants has been based on a limited number of analytical techniques. One of the most important analyses has always been the total base number (TBN) measurement. Although the TBN measurements are informative, easy, and quick, it can be misleading to base the judgment of an oil's performance solely on one criterion. This paper offers observations from a field test, showing that some detergent approaches gave unacceptable performance even though the TBNs were at an acceptable level. It is hypothesized that some detergents do not effectively neutralize all acidic species present in the lubricant, thereby reserving their own base while in fact the oil may no longer provide sufficient protection against bearing corrosion. This hypothesis is supported with bench and engine test data. It is recommended that, at a minimum, total acid number (TAN) measurements be included in any analysis.