Diesel particulate filters (DPF), known as traps in the mid-to late 1970s, were being developed for on-highway diesel applications. However, advanced engine design and in-cylinder engineering enabled diesel engines and vehicles to meet extremely low emission limits, including those of particulate matter (PM) without the need for DPF's or other auxiliary emission control devices.
Late in 2000, the US EPA finalized its on-highway heavy-duty diesel emission standards, thus ending speculations regarding its stringency and establishing the lowest limits ever. The new nitric oxides (NOX) and PM limits are seen as technology-forcing. For NOX emissions, the debate rages on among the technical community about the merits of NOX adsorbers and urea selective catalytic reduction. On the other hand, there seems to be little doubt about DPF's as the technical solution for PM.
While early DPF designs suffered tremendously from their lack of reliability and durability, continued development has produced a new breed of DPF's. To date, one European passenger car manufacturer (PSA) has included DPF's in their product mix. The same manufacturer is also teaming up with Ford of Europe to expand the use of principally the same system.[1] The State of California has also approved two DPF systems to be used on diesel engine-equipped vehicles [2, 3] after having apparently established that diesel exhaust was a toxic air contaminant. Whether DPF's are currently used for OEM or retrofit applications, it behooves us to consider whether or not the technology is capable of meeting rigorous heavy-duty requirements especially those of predictable and safe regeneration at all conditions as well as long-term durability of as much as 435,000 miles.
This paper reviews some of the DPF technology advances and discusses future directions and developments that may be required for future diesel engines and vehicles.