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

Abstract

The Euro IV emission standards for heavy-duty diesel vehicles require a substantial reduction in NO x emissions, spurring the introduction of selective catalytic reduction (SCR) systems. However, previous studies have found unsatisfactory control of NO x 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 NO x emissions between Euro II and Euro III HDDTs. In contrast, we observed a substantial reduction in real-world NO x 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 NO x emission factors for the SCRequipped HDDTs were higher by ~45% than the lab test limit of 3.5 g kWh -1 due to off-cycle NO x 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 NO x emission factors steadily decrease as the vehicle speed increases due to higher exhaust temperatures, which improve the efficiency of SCR systems.

A transition of atmospheric emissions of particles and gases from on-road heavy-duty trucks

“…Euro VI HDTs have a higher NO 2 fraction, because the DOC upstream of the filter is used to convert NO to NO 2 to control the soot loading in the DPF and facilitate the passive regeneration (Van Setten et al, 2001). A failure of the NO 2 reduction due to the inactivity of the SCR, resulting from low exhaust gas temperature, may yield a higher NO 2 emission (Bishop et al, 2010;Heeb et al, 2010;Herner et al, 2009;May et al, 2014;Thiruvengadam et al, 2015). A more significant decrease in NO x than NO 2 emissions of Euro VI HDTs may cause an increase in EF NO 2 /EF NO x .…”

Impact of Hydrothermal Aging on SO2 Poisoning over Cu-SSZ-13 Diesel Exhaust SCR Catalysts

“…As one of the major sources of nitrogen oxides (NO X ) in the U.S and China, heavy-duty diesel (HDD) has made a considerable contribution to NO X emissions. − To meet the increasingly restricted NO X limits in the current emission standards, selective catalytic reduction (SCR) has been widely used as the current leading technology for NO X abatement of heavy-duty diesel. − The NO X emissions should be held under the limits during the entire lifetime of the SCR converter, which requires better durability of the catalysts . Therefore, understanding the mechanism of the SCR catalyst deactivation is critical.…”

Exhaust Emissions from a Hybrid City Bus Fuelled by Conventional and Oxygenated Fuel

“…Over the last 20 years or so, exhaust emissions from diesel vehicles have been significantly reduced. First of all, thanks to the use of advanced injection systems and effective exhaust aftertreatment systems [9][10][11][12]. This is perfectly illustrated by the lower and lower levels of exhaust emissions permitted by law [13,14].…”