Particle Oxidation Catalyst (POC ^® ) - From Diesel To GDI - Studies on Particulate Number and Mass Efficiency 2012-01-0845

Legislations worldwide have started imposing stringent emission standards for particulate matter (PM) emitted by diesel engines. The main reason for these actions is the adverse effects on human health caused by particle emissions. Conventional ceramic Diesel Particulate Filters (DPF) have proven exceptionally effective in reducing particulate emissions with efficiencies of 90% or more. However, these filters require regular active regenerations as well as periodical ash removal in order to avoid a blockage of the exhaust line. These procedures are both costly and complex and as a result alternative aftertreatment solutions have been developed. One of these solutions is the Particle Oxidation Catalyst, POC-X. The main aim of the POC-X is not to equal the high efficiencies of the DPF, but to achieve the best possible particle reduction without creating the risk of blocking or the need for complex filter regeneration procedures.

The substrate used in the POC-X is a fine mesh screen made of metal, which is rolled into a cylinder and placed into the exhaust line. The unique construction forms tortuous channels which run through the filter. This means that the exhaust gas can either flow through the substrate cells, which act as trapping agents for soot particles, or along the tortuous channels should the filter become overloaded. Additionally, a specially developed washcoat is applied to the substrate in order to facilitate the production of Nitrogen dioxide (NO₂), which aids the regeneration process of the filter.

In an experimental study, the performance of the POC-X has been investigated using a 1.6-liter, Euro 4 diesel engine on a dynamic test bench. Sophisticated exhaust gas measurement equipment supplied by Horiba was used to evaluate soot, soluble organic fraction (SOF), particle number (PN) as well as gaseous emissions in real time (1 Hz) during stationary and dynamic measurements. For the dynamic tests, the new European driving cycle (NEDC) was used. The combination of these measurements provided an accurate performance picture of the POC-X. By evaluating a variety of POC-X sizes, the optimum filter dimensions and key parameters were determined. Furthermore, by conducting a series of particle size distribution measurements using a scanning mobility particle sizer (SMPS), the relationship between particle size and filter efficiency was investigated. Based on these results, a calculation model is being developed, which will support the design and application of the POC-X based on engine operating parameters and filter dimensions. This will allow for efficiently designed solutions to specific applications.

As particulate emission limitations are also being implemented for gasoline direct injection (GDI) technologies, a new POC prototype has been tested in a GDI vehicle with a short, on-road, durability run.