Full flow particulate filters are a state of the art solution
for many serial production diesel engine applications. They are
very effective for removing ≻ 90% of particulate mass and ≻ 99% of
the particulate number from the exhaust gas of diesel engines. Many
diesel engines have to work at load profiles which necessitate
active regeneration procedures to ensure continued engine operation
and the reliability of the full flow particulate filter. Passive
regeneration via NO₂, as a cost-effective solution, cannot be used
as the sole method for all applications, due to restrictions such
as, insufficient engine-out NOX/PM ratio, low exhaust gas
temperature level or occasionally poor fuel quality. To meet the
Tier 4 emission legislation casually partial flow particulate
filters enable sufficient particulate reduction at boundary
conditions where full flow DPF is not applicable.
This paper discusses the influences of boundary conditions on
the performance of partial flow sintered metal particulate filters
and their relevance for Tier 4 applications. The filtration
efficiency is controlled via design of the filter in conjunction
with the DOC layout. By means of NO₂ formed in the DOC the
regeneration of the soot retained in the filter is carried out. Due
to the increased variance sufficient filtration efficiency can be
granted at NOX/PM ratios partially less than 1/3 as required for
full filter CRT applications and even at lower exhaust gas
temperatures. Depending on soot loading variable efficiency,
periods with very poor regeneration performance can be covered. The
presented partial flow particulate filter gives almost equal
reduction of PM and PN between 30% and 70%. Backpressure or
filtration efficiency can be adjusted nearly independent from the
substrate volume. Due to the special design the ash retention of
the partial flow sintered metal filter is negligible. The
realization of a stage/Euro 4 application, based on a stage 3
engine is shown by real applications.
