Detailed Chemical and Physical Characterization of Ash Species in Diesel Exhaust Entering Aftertreatment Systems 2007-01-0318

Irreversible plugging of diesel particulate filters caused by lubricant-derived metallic ash is the single most important factor responsible for long-term performance degradation and reduction in the service life of these filters. While a number of studies in the open literature have already demonstrated the benefits of diesel particulate traps and highlighted some of the difficulties associated with trap operation, many specific factors affecting trap performance and service life are still not well understood. The exact composition and nature of the exhaust entering the trap is one of the most important parameters affecting both short-term trap operation and long-term durability.

In this study a fully instrumented Cummins ISB 300 six-cylinder, 5.9 liter, diesel engine was outfitted with a diesel particulate filter and subjected to a subset of the Euro III 13-mode stationary test cycle. Total throughputs of various elements including sulfur and metallic ash, and their distributions in solid, liquid, and gaseous (SO₂) forms were examined. Variations in particulate and ash chemical and elemental composition were quantified via detailed chemical and thermal analysis, which included TGA, ICP, and STEM. In addition, variations in particulate SOF, SOL, and SO₄, as well as total ash content were measured before and after the diesel particulate filter. Changes in particulate and ash morphology were investigated using SEM and TEM analysis. Furthermore, the impact of lubricant sulfur content on the distribution of exhaust sulfur between gaseous SO₂ and particulate SO₄ was measured. Significant differences in the distribution of metallic, sulfur, and phosphorous compounds in the ash and bulk particulates were observed. These measurements constitute the first step in understanding exhaust chemical conditions and correlating their effects with aftertreatment system performance, and degradation thereof, if any.