Optical and Analytical Studies on DPF Soot Properties and Consequences for Regeneration Behavior

The removal of particulate matter (PM) from diesel exhaust is necessary to protect the environment and human health. To meet the strict emission standards for diesel engines an additional exhaust aftertreatment system is essential. Diesel particulate filters (DPF) are established devices to remove emitted PM from diesel exhaust. But the deposition and the accumulation of soot in the DPF influence the filter back pressure and therefore the engine performance and the fuel consumption. Thus a periodical regeneration through PM oxidation is necessary. The oxidation behavior should result in an effective regeneration mode that minimizes the fuel penalty and limits the temperature rise while maintaining a high regeneration efficiency. Excessive and fast regenerations have to be avoided as well as uncontrolled oxidations, which may lead to damages of the filter and fuel penalty. The thermal control during the soot oxidation poses a challenge resulting from the lack of knowledge concerning the operation behavior of the DPF.

In this study, a method to investigate the influences of operating conditions on the inflow and the soot deposition inside the DPF as well as the following regeneration is presented. For that purpose, the inflow is visualized by Particle Image Velocimetry (PIV) to identify the origins of the nonuniform soot distribution inside the DPF. Structural changes of the deposited soot are studied via Raman Spectroscopy. The distribution of inorganic ash components is studied via laser ablation with Inductively-coupled plasma mass spectrometry (LA-ICP-MS). Soot reactivity is quantified with Thermogravimetric Analysis (TGA) and the calculation of oxidation kinetics. By combining analytical and optical measurement techniques the influences of the physical and chemical properties of the soot on the regeneration process can be derived. Furthermore, possibilities can be demonstrated how to manage regeneration processes at lower exhaust temperatures which result from improvements of combustion engines and hybridization.