Diesel particulate filter loading and regeneration issues in city/congested driving

Abstract

Diesel particulate filters (DPF) are a widely used after-treatment method adopted in current diesel engines and the Gasoline Particulate Filter (GPF) is in the pipeline for future gasoline direct injection. The DPF accumulates soot from normal engine running and is then expected to burn off the accumulated soot during regeneration instances. The regeneration instance can be both due to normal engine driving or is Engine Control Unit (ECU) assisted. In city or congested driving situations, the regeneration can be difficult to achieve. Such slow speed driving is also the case in a small island as Malta. Many people are experiencing DPF blockage problems which sometimes lead to undrivable vehicles. The ECU monitors the level of loading mainly through the differential pressure sensor. This paper discusses soot loading models currently available in the literature and their performance vis-à-vis the actual soot loading level is analyzed. It was determined that different models lead to disagreement in predicted delta p. The widest discrepancy between models was of more than a factor of 10. Physical weight measurement of soot loading from soot blocked DPFs was conducted by oxidation in a furnace. The residues leftover from the furnace regeneration were also analyzed and the soot/ash ratio was quantified. It was determined that the ash left is very low, meaning that the DPFs were blocked with soot and not ash. This was attributed to the inability to have regeneration of the DPF whilst driving to the very low speed low load driving conditions experienced in Malta.