Effect of Biofuels on Catalyzed Diesel Particulate Filter Regeneration

Under the terms of the Renewable Energy Directive, EU member states are required to use 10 % of transport energy sourced from renewable sources, mainly biofuels, by 2020. The purpose is to reduce greenhouse gas (GHG) emissions from the transport sector. However, biodiesel used as fuel has a significant impact on emissions, as related by most of the literature on the subject. In particular, nitric oxides (NOx) and particulate matter (PM) emissions from current diesel technologies are critical factors because they are already close to the limits permitted by regulations and both limits will be even more stringent in the near future. Soot particles are trapped on a diesel particulate filter (DPF). If the DPF is catalyzed like in this study, the soot is then burned by reaction with NO₂ (CDPF continuous regeneration) which occurs at lower temperatures than reaction with O₂ (active regeneration). Tests of ultra-low sulfur diesel blended with rapeseed-biodiesel at 30 % (B30) and Fischer–Tropsch diesel (FT30) were conducted. The Fischer–Tropsch diesel was chosen to represent a biomass-to-liquid fuel. This work investigated the impact of these two biofuels on engine polluting emissions and the resulting CDPF ability to regenerate. When compared with similar inlet conditions on a synthetic gas bench, an impact of fuel was observed on soot reactivity: the CDPF loaded with FT30 soot regenerated slightly faster. Engine bench tests were also performed to combine the effects of fuel on engine emissions and soot reactivity and to evaluate the CDPF. The increase in NOx and decrease in PM emissions observed for B30 appeared to significantly improve CDPF continuous regeneration by NO₂.