An experimental investigation of particle and NOx emissions for a non-road diesel engine equipped with an integrated DOC + CDPF + SCR aftertreatment system during different operations.

Abstract

An integrated aftertreatment system consisting of diesel oxidation catalyst (DOC), catalytic diesel particulate filter (CDPF), and selective catalytic reduction (SCR) is an effective way of reducing both NOx and particulate matter (PM). In this paper, the effect of DOC + CDPF + SCR on NOX and particle emissions is investigated during different operations to assess applicability of this aftertreatment for meeting more rigorous non-road emissions standard. Meanwhile non-negligible issue about regeneration emission is studied. The results show that the DOC + CDPF have no significant effect on NOx but increase the NO2/NOx ratio which is correlated with load. SCR is the main NOx reduction device with average efficiency of 86.5% for steady-state operations. Meanwhile, NH3 slip is lower than 16ppm. During cold and hot non-road transient cycles (NRTCcycles), average NOx efficiencies are 56.7% and 57.8%, respectively, along with NH3 slip below 10ppm. DOC + CDPF + SCR maintain filtration efficiency over 97% and 99% for PM and particle number (PN) for either steady-state operation or NRTCcycle, but particle size distributions change. Compared with the original emissions, NOx, PM, and PN emission factors are all below non-road China-IV limit after equipping with DOC + CDPF + SCR. However, during regeneration the aftertreatment does not maintain a high filtration performance but becomes particle generator. The penetration of nuclear particles and decomposition of agglomerated particles lead to high CDPF-out PN of 1.5 × 107 #/cm3-3.5 × 107 #/cm3. During regeneration, accumulated NOx is negligible, but the PM is 121.6 and 44.5 times higher than cold and hot NRTCcycles, respectively. In summary, DOC + CDPF + SCR is excellent way to improve non-road emissions but low SCR efficiency at low-temperature and high accumulated PM during regeneration process should be further addressed.