Emission characteristics and performance of SCR coated on DPF with different soot loads

Abstract

Selective catalytic reduction (SCR) catalyst coated on diesel particulate filters (DPF), term as SDPF, become a popular subject of current research due to the capability of improving the NOx conversion efficiency and catalytic activity under low-temperature and low-load conditions. This study investigated the impact of SDPF emission characteristics and performance with different soot loads. The results showed that, soot load had little effect on engine fuel consumption. With the increase in soot load, the pressure drop and SDPF inlet temperature showed an upward trend, and the NOx conversion efficiency decreased sharply. NOx conversion efficiency was the result of competition between exhaust temperature and NO2 concentration. When the soot load was 9.97 g/L, SDPF lost the ability to reduce NOx emission. SDPF could reduce nucleation-mode particle number (PN) emission by 2–3 orders of magnitude, the filtration efficiency of nucleation-mode PN emission was the competition result between physical collection mechanism and chemical reaction. The particle diameter of particles with passive regeneration reaction with NO2 ranges from 10.8 to 45.3 nm. SDPF could reduce the accumulation-mode PN emission by 1–2 orders of magnitude, and the filtration efficiency of accumulation-mode PN emission was greatly affected by the physical collection mechanism. Increasing the soot load of SDPF could effectively reduce the nucleation-mode PN emission, but had no obvious effect on the accumulation-mode. At low engine speed, the filtration efficiency of nucleation-mode and accumulation-mode PN increased significantly with the increase in the SDPF soot loads. The maximum filtration efficiencies of nucleation-mode, accumulation-mode, and total PN were 99.93 %, 99.36 %, and 99.56 %, respectively. With the increase in soot load, the geometric mean diameter of SDPF-out increased.