Emission characteristics of a diesel engine with an electrically heated catalyst under cold start conditions

Abstract

The high emissions of diesel engines at cold start conditions have attracted more and more attention, because the exhaust gas temperature at this condition is too low to light-off the aftertreatment system. The electrically heated catalyst (EHC) has a high potential for increasing exhaust gas temperature and thus lowering emissions from diesel engines under cold start conditions. In this study, based on a diesel engine with an aftertreatment system that an EHC was installed in the inlet of a diesel oxidation catalyst (DOC), the engine was cold started to a low-load operating point (1000 r/min, 56 N m) and the World Harmonized Transient Cycle (WHTC). The influence of the EHC on the exhaust gas temperature and emission characteristics under the two cold start conditions is investigated. When EHC-on as opposed to EHC-off, the time required for the exhaust gas temperature at post-DOC to reach 138°C was shortened by 767 s during the low-load cold start process, and the time required to reach 200°C was reduced by 418 s during the WHTC cold start process. The total conversion efficiencies of CO and HC increased by 92.8% and 50.8% respectively in the warm up process of the low-load cold start, and the increases were 39.8% and 38.5% respectively in the urban driving cycle of the WHTC cold start process. It was found that the particulate number (PN) concentration at post-DOC increased when EHC-on, and the proportion of nucleation-mode particulates also increased.