Development of a zeolite-based (HC Trap type) cold-start catalyst (CSC) for meeting Tier4/LEV IV tailpipe emission standards, Part IV

This is a follow-up paper to the three previous reports [1, 2&3] regarding the development of a zeolite-based hydrocarbon (HC/NOx) trap-type of cold-start catalyst (CSC) as a cost-effective approach to meet future more stringent vehicle tailpipe emission standards, such as Tier 4/LEV IV. One of the main challenges of meeting Tier 4/LEV IV tailpipe emission standards is both SC03 and US06 test cycles start at room temperature (cold) in steady of at elevated temperature (hot) in Tier 3/LEV III. In this paper, a hybrid vehicle with a Tier3 Bin30 and a Tier3 Bin20 certified aftertreatment systems were tested in cold SC03 and cold US06 cycles. It requires about 64% and 52% tailpipe emissions reduction, respectively, in cold SC03 for the HEV with these two aftertreatment systems to meet Tier 4/LEV IV Bin30 tailpipe emission engineering target of (NOx+NMHC) 13.13 mg/mile. In cold US06 tests, it requires to decrease 50% and 38% of tailpipe emissions, respectively, for the HEV with these two aftertreatment systems to meet the same engineering target. The increased tailpipe emissions in cold tests over the hot tests of the same cycles is due to the raised cold-start emissions. The CSC developed in this work was applied to modify the Tier3/LEV III Bin20 aftertreatment system, and the vehicle tests were performed in both cold SC03 and cold US06 cycles with the CSC modified aftertreatment system. The CSC effectively decreased the tailpipe cold-start emissions (NMHC+NOx) in cold SC03 and cold US06 cycle tests and helped the HEV vehicle meet Tier 4 /LEV IV Bin 30 engineering target of 13.13 mg/mile. The detailed emission results will be reviewed in this manuscript. The impacts of zeolite loading & Pd in zeolite loading on the CSC performance were also studied.