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Investigating Real-World Emissions of China’s Heavy-Duty Diesel Trucks: Can SCR Effectively Mitigate NOx Emissions for Highway Trucks?

Category: Control Techniques and Strategy

Article In Press
DOI: 10.4209/aaqr.2016.12.0531
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Liqiang He1,2, Jingnan Hu 2,3, Shaojun Zhang1,4, Ye Wu 1, Xing Guo2, Xing Guo2, Jinghao Song2, Lei Zu2, Xuan Zheng1, Xiaofeng Bao2

  • 1 School of Environment, State Key Joint Laboratory of Environment Simulation and Pollution Control, Tsinghua University, Beijing 100084, China
  • 2 State Environmental Protection Key Laboratory of Vehicle Emission Control and Simulation, Chinese Research Academy of Environmental Sciences, Beijing 100012, China
  • 3 Collaborative Innovation Center of Atmospheric Environment and Equipment Technology (CICAEET), Nanjing 210044, China
  • 4 Sibley School of Mechanical and Aerospace Engineering, Cornell University, Ithaca, NY 14853, USA

Highlights

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.


Abstract

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.

Keywords

Heavy-duty diesel trucks NOx emission PEMS SCR


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