NOx emission deterioration in modern heavy-duty diesel vehicles based on long-term real driving measurements

Liqun Lyu; Zhongrui Ji; Hang Yin; Junfang Wang; Wenjuan Yang; Jianwei Tan; Lijun Hao; Xin Wang; Huaiyu Wang; Yunshan Ge; Yachao Wang

doi:10.1016/j.envres.2023.116396

NOx emission deterioration in modern heavy-duty diesel vehicles based on long-term real driving measurements

Environ Res. 2023 Sep 1:232:116396. doi: 10.1016/j.envres.2023.116396. Epub 2023 Jun 14.

Authors

Liqun Lyu¹, Zhongrui Ji², Hang Yin³, Junfang Wang³, Wenjuan Yang⁴, Jianwei Tan¹, Lijun Hao¹, Xin Wang¹, Huaiyu Wang¹, Yunshan Ge⁵, Yachao Wang¹

Affiliations

¹ School of Mechanical Engineering, Beijing Institute of Technology, Beijing, 100081, China.
² Emission Regulation Office, Weichai Power Co., Ltd., Weifang, 261061, China.
³ State Environmental Protection Key Laboratory of Vehicle Emission Control and Simulation, Chinese Research Academy of Environmental Sciences, Beijing, 100012, China.
⁴ Shandong Shengxiang Intelligent Manufacturing Co., Ltd., Weifang, 262100, China.
⁵ School of Mechanical Engineering, Beijing Institute of Technology, Beijing, 100081, China. Electronic address: geyunshan@bit.edu.cn.

PMID: 37327837
DOI: 10.1016/j.envres.2023.116396

Abstract

NOx emissions from diesel vehicles generally deteriorate with increased durability mileage owing to the wear and deterioration of engines and after-treatment systems. Three China-VI heavy-duty diesel vehicles (HDDVs) were selected for four-phase long-term real driving emission (RDE) tests using the portable emission measurement system (PEMS). After 200,000 km of on-road driving, the maximum NOx emission factor of the test vehicles (387.06 mg/kWh) was found to be significantly lower than the NOx limit of 690 mg/kWh. Under all driving conditions, the NOx conversion efficiency of selected catalytic reduction (SCR) decreased almost linearly as the durability mileage increased. Importantly, the deterioration rate of the NOx conversion efficiency in low-temperature intervals was discernibly higher than that in high-temperature intervals. The NOx conversion efficiency at 200 °C dropped by 16.67-19.82% with higher durability mileage; however, the highest values at 275-400 °C only decreased by 4.11%. Interestingly, the SCR catalyst at 250 °C showed strong NOx conversion efficiency and durability (maximum decline of 2.11%). Overall, the poor de-NOx performance of SCR catalysts at low temperatures significantly challenges the long-term effective control of NOx emissions from HDDVs. Thus, improving the NOx conversion efficiency and durability at low-temperature intervals is the top priority for SCR catalyst optimization; NOx emissions from HDDVs at low velocities and loads should also be monitored by environmental authorities. The linear fitting coefficient for the NOx emission factors of the four-phase RDE tests was 0.90-0.92, indicating that NOx emissions deteriorated linearly with an increase in mileage. Based on the linear fitting results, the NOx emission control of the test vehicles during 700,000 km of on-road driving was highly likely to be qualified. These results can be used by environmental authorities to supervise the NOx emission conformity of in-use HDDVs after validation using other types of vehicles.

Keywords: Heavy-duty diesel vehicle; NOx emission deterioration; PEMS; Real driving emission; SCR.

MeSH terms

Air Pollutants* / analysis
Catalysis
China
Gasoline
Motor Vehicles
Vehicle Emissions / analysis

Substances

Air Pollutants
Vehicle Emissions
Gasoline