Microscopy investigations of ash and particulate matter accumulation in diesel particulate filter surface pores

Abstract

There has been increased focus on the environmental impact of automobile emissions in recent years. These environmental concerns have resulted in the creation of more stringent particulate matter emissions regulations in the United States and European Union. These limits have forced diesel engine manufacturers to reduce particulate matter (PM) emissions by an order of magnitude beginning in 2007. Diesel particulate filters (DPF) provide the most effective means of reducing PM emissions from diesel exhaust. DPFs can reduce over 99% of PM in the exhaust. DPF effectiveness is limited by the accumulation of ash. Ash is comprised of incombustible material from engine lubricants. Engine oil additives based on P, Zn, S, Ca, and Mg are responsible for the majority of ash. Ash accumulation in DPFs reduces their useful life by plugging the filter's inlet channels. Ash deposition leads to increased pressure drop across the DPF, which reduces the engine's performance and negatively impacts fuel economy. The process of ash accumulation in DPF channels is not well understood. This research is focused on exploring the ash interactions with DPF walls, pores, and the catalyst washcoat. Based on scanning electron microscopy analysis of ash loaded DPFs from the field and from filters loaded with ash in the laboratory, a mechanism for ash accumulation is presented.