Abstract
A 6.2 L diesel engine that meets China VI emission standard was selected to run world harmonized transient cycle (WHTC) and California Low Load Cycle (LLC) to measure the pollutants. The brake specific emission under the two cycles were compared, and nitrogen oxides (NOx) emission were analyzed carefully. The results show that the NOx emission of the LLC of this engine is about 15 times than that of the hot WHTC, and 4.7 times than that of the limitation of current China VI emission standard. The low inlet temperature of selective catalytic reduction (SCR) is the predominant reason for the high NOx emission in the LLC. The SCR inlet temperature of lower than 200°C in LLC accounts for 52% of the total time with an average inlet temperature of only 190°C. While the inlet temperature of lower than 200°C of the hot WHTC only accounts for 7% with the average inlet temperature of 275°C. The average SCR catalytic efficiency calculated by NOx sensor amounted on the upstream and downstream of LLC is only 75%, while the efficiency is 98% for hot WHTC. It is necessary to focus on thermal management of the aftertreatment system and the SCR catalytic performance at low temperature.
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