17 July 2002
The Road Safety and Transportation Agency, a part of the Danish Ministry of Traffic, has published a final report summarizing the experience from a diesel particulate filter (DPF) demonstration project conducted over a period of more than two years in Odense, the third largest city in Denmark.
The report concludes that DPFs removed about 80% of diesel particulate matter (PM) emissions, with regard to all particle sizes. The filters were also found effective in removing the smallest particles, including ultra-fine and nanoparticles of diameters between 10-100 nanometers, which are suspected to pose more adverse health effects to humans than larger particles.
It was also found, however, that the particulate filter system has to be carefully chosen for a given type of vehicle and duty cycle, and that the vehicles have to be properly maintained to assure problem-free operation of the DPF. For instance, passively regenerated filters may experience problems when installed on vehicles characterized with low exhaust temperatures, such as waste collection trucks. Among the tested DPFs, a fuel additive-regenerated filter and an active, electrically regenerated system (considerably more expensive than the others) were found to perform best in low temperature applications. Most filter systems have passed the durability test, remaining effective over the two-year duration of the project.
A certain increase in nitrogen dioxide emission was noted in catalytic DPFs due to the oxidation of nitric oxide.
The project involved retrofitting of 120 vehicles, mostly buses and trucks, with various types of particulate filters, including (1) Johnson Matthey: CRT, (2) Engelhard: DPX, (3) Silentor fuel additive filter system , (4) Energitechnik Bremen: electrically regenerated filter. In addition, three combined DPF/NOx control systems were evaluated, including (1) Svensk Turbo Teknik EGR, (2) Ferita EGR, (3) Ceryx: QuadCat (the company has since closed).
At this time, the final report from the study is available only in Danish.
Source: Danish Ecological Council