NH3 and N2O emission durability of the heavy-duty diesel engine with DOC, DPF, SCR, and ASC through the accelerated aging method

Abstract

A general accelerated aging method for aftertreatment devices of Heavy-duty Diesel Engine (HDDE) is proposed in this paper, and three sets of aftertreatment devices were aged according to this method. The error between the World Harmonized Transient Cycle (WHTC)-NOx emission factors of conventional aging and those of accelerated aging fitted by equivalent thermal accumulation is −4.12 to 3.13 %, which proves that the two methods have good equivalence. Meanwhile, the NH3 and N2O emission characteristics and durability were tested by Fourier Transform Infra-Red Spectroscopy (FTIR) equipment. The results show that NH3 and N2O emissions do not deteriorate linearly with the intensification of thermal aging like NOx. Except that the NH3 emission of AT03 exceeds the limit of China VI emission regulation (the average and maximum NH3 concentration in the WHTC test are 35.25 ppm and 350.30 ppm, separately), NH3 emission of other aged devices meet the requirements. Combined with the equivalent durability mileage of 1130000 km of AT02, the test China VI HDDE can effectively control NH3 emissions and has a large margin with the limit requirements. However, the deterioration rate of N2O emission gradually slows down with the intensification of accelerated aging. The accelerated aging tests also indicate that N2O generation is closely related to NH3 in SCR, consistent with previous studies conclusions of low-temperature and high-temperature N2O generation mechanisms. Equally important is that the N2O emission emitted from test China VI HDDE is significantly higher than the emission limit of the Environmental Protection Agency (EPA). The N2O emission factors under the WHTC test are as high as 0.15 to 0.35 g/kWh, which should draw the attention of Chinese environmental regulatory authorities, who should start to formulate N2O emission limits and put forward complementary strategies to reduce N2O emissions from HDDEs.