Abstract
ABSTRACTThe 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.
Highlights
The real-world brake-specific NOx emission factors for Euro II, III and IV heavy-duty diesel trucks (HDDTs), which are listed in Table 3, are higher than their corresponding laboratory emission limits (i.e., 7.0, 5.0 and 3.5 g kWh–1 for Euro II, III and IV HDDTs based on laboratory engine bench tests, respectively) by 47%, 97% and 45%, respectively, similar to the gaps between real-world emissions and regulatory limits previously reported by Wu et al (2012)
We analyzed the impacts of real-world operating conditions on NOx emissions, with a special focus on six HDDTs equipped with selective catalytic reduction (SCR) systems
We found no significant reduction in real-world NOx emissions as the emission standards tightened from Euro II to Euro III
Summary
Heavy-duty diesel vehicles (HDDVs) have been identified as one of the most important contributors to air pollution, health impacts and climate change (Johnson et al, 2009; Wu et al, 2011; Silverman et al, 2012; Bond et al, 2013; Zhang et al, 2013; Wu et al, 2014) and have contributed to an ascending trend in China’s total anthropogenic NOx emissions (Richter et al, 2005; Wu et al, 2012; Zhao et al., 2013). According to the official report released by the MEP (2012), total NOx emissions from on-road vehicles in China were 6.4 Tg in 2011, 67% of these emissions were contributed by HDDVs (including public transit buses, highway trucks and coach buses). Wu et al (2012) estimated that the total NOx emissions of the national HDDV fleet in 2009 exceeded the amount provided in the
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