Cite this article: He, L., Hu, J., Zhang, S., Wu, Y., Guo, X., Guo, X., Song, J., Zu, L., Zheng, X. and Bao, X. (2017). Investigating Real-World Emissions of China’s Heavy-Duty Diesel Trucks: Can SCR Effectively Mitigate NOx Emissions for Highway Trucks?.
Aerosol Air Qual. Res.
17: 2585-2594. https://doi.org/10.4209/aaqr.2016.12.0531
Sixteen HDDTs were tested by PEMS on three typical roads and with different loads.
The HDDTs with SCR reduce on-road NOx emissions by 50% relative to those without SCR.
On-road NOx emissions form HDDTs with SCR are higher by 45% than the lab test limit.
Higher speeds improve SCR efficiency and reduce NOx emissions form HDDTs with SCR.
The Euro IV emission standards for heavy-duty diesel vehicles require a substantial reduction in NOx emissions, spurring the introduction of selective catalytic reduction (SCR) systems. However, previous studies have found unsatisfactory control of NOx emissions for SCR-equipped urban buses, which has raised concern among policy-makers and researchers regarding the capability of SCR adopted by heavy-duty diesel trucks (HDDTs) in real-world applications. This study tested sixteen HDDTs in China between 2010 and 2014, including six SCR-equipped Euro IV HDDTs using a portable emissions measurement system (PEMS). On-road emission measurement results show no significant difference in NOx emissions between Euro II and Euro III HDDTs. In contrast, we observed a substantial reduction in real-world NOx emissions, as low as 25.4 g kg-fuel–1, for six SCR-equipped HDDTs (Euro IV) compared with those without SCR systems (Euro II and Euro III), providing an overall reduction of ~50%. However, real-world brake-specific NOx emission factors for the SCR-equipped HDDTs were higher by ~45% than the lab test limit of 3.5 g kWh–1 due to off-cycle NOx emissions, indicating the importance of introducing real-world emission test requirements for HDDTs. Due to the introduction of SCR systems, distinctive impacts from real-world operating conditions are observed for HDDTs. For example, fuel-based NOx emission factors steadily decrease as the vehicle speed increases due to higher exhaust temperatures, which improve the efficiency of SCR systems.