Emission Characteristics of a Light Diesel Engine with PNA under Different Coupling Modes of EHC and Aftertreatment System

Abstract

<div class="section abstract">With the continuous upgrading of emission regulations, NOx emission limit is becoming more and more strict, especially in the cold start phase. Passive NOx absorber (PNA) can adsorb NOx at a relatively low exhaust temperature, electrically heated catalyst (EHC) has great potential to improve exhaust gas temperature and reduce pollutant emissions of diesel engines at cold start conditions, while experimental research on the combined use of these two kinds of catalysts and the coupling mode of the electrically heated catalyst and the aftertreatment system under the cold start condition are lacking. In this paper, under a certain cold start and medium-high temperature phase, the exhaust gas temperature and emission characteristics of PNA, EHC and aftertreatment system under different coupling modes were studied. Results showed that the average inlet temperature of diesel oxidation catalyst (DOC) and selective catalytic reduction catalyst (SCR) integrated into diesel particulate filter (SDPF) increased by 246.35 ℃ and 126.09 ℃ respectively under the coupling mode of PNA+EHC+DOC+ SDPF+SCR during cold start phase. The inlet temperature of DOC was not affected, and the average inlet temperature of SDPF increased by 200.52 ℃ under the coupling mode of PNA+DOC+EHC+SDPF+SCR. In terms of emissions, the effective NOx adsorption range of PNA reached more than 140s under the two coupling modes. During cold start phase, under the coupling mode of PNA+EHC+DOC+SDPF+SCR, the conversion efficiencies of carbon monoxide (CO), total hydrocarbons (THC) and nitrogen oxides (NOx) were 97.58%, 94.62% and 78.81% respectively, compared with EHC off, it had increased by 55.84%, 55.84% and 55.84% respectively. Under the coupling mode of PNA+DOC+EHC+SDPF+SCR, the conversion efficiencies of CO, THC and NOx were 58.68%, 87.50% and 95.42% respectively, compared with EHC off, it had increased by 15.91%, 11.70% and 51.41% respectively. EHC coupled front DOC was more conducive to CO and THC emission control, and EHC coupled rear DOC was more conducive to NOx emission control. The SDPF pressure drop corresponding to EHC coupled front DOC was greater than that of EHC coupled rear DOC, the PN conversion efficiency of EHC coupled front or rear DOC was more than 99%. </div>