Partial Flow Sintered Metal Filter as Part of a Tier 4 Emission Reduction Strategy 2012-01-1731

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 NO_X/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 NO_X/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.