Performance Improvement of Diesel Particulate Filter by Layer Coating

Nowadays diesel particulate filters (DPFs) with catalyst coatings have assumed one of the most significant roles for road vehicle emission control. DPFs made of re-crystallized SiC (SiC-DPFs) have guaranteed the soot filtration efficiency for the current regulation. In order to further enhance their filtration efficiency, even though a higher porosity and larger pore size must be adopted for sufficient catalyst coating capacity, we developed the concept of a filtration layer on the DPF inlet channel walls and researched its performance both theoretically and experimentally. First of all, models of the new filtration layer, closely resembling the real one made in the laboratory, were digitally reconstructed and soot deposition simulations were conducted. According to the results, the pore size of the filtration layer providing the target filtration efficiency is found to be between the characteristic soot particle size (of order 100 nm) and the nominal DPF wall pore size (of order 10 μm). Additionally, it is shown that the optimum spatial distribution of filtration layer thickness along DPF length should be matched to the filtration velocity distribution. Finally we experimentally verified the performances of SiC-DPF with filtration layer by engine bench tests. We found that very high filtration efficiency is attained while it is shown that the concept presented can bring 3 significant advantages through its use: a high initial filtration efficiency of 97% in spite of a higher porosity SiC-DPF wall, an 18% decrease of transient pressure drop at 4 g/L soot mass in DPF without increased initial pressure drop due to a deep-bedding of soot, and a repeatability of transient pressure drop after several loading-regeneration cycles.