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.