On-road GHG emissions characteristics and durability of typical China-VI HDDVs in intercity transportation

Abstract

China confronts rising greenhouse gas (GHG) emissions from transportation sector, particularly under-addressed emissions from heavy-duty diesel vehicles (HDDVs), challenging its carbon neutrality goal by 2060. Using a portable emission measurement system (PEMS), the on-road CO₂, CH₄, and N₂O emissions characteristics and durability of seven typical China-VI HDDVs applied for intercity transportation were evaluated. A direct correlation was observed between increased instantaneous CO₂ emissions and vehicle specific power (VSP), affirming the positive dependency of CO₂ emissions on engine power. However, CH₄ emissions remained negligible across various speeds, displaying no obvious correlation with VSP, suggesting that power fluctuations were not the primary factor impacting the CH₄. N₂O emissions, on the other hand, were independent of speed but increased with increasing VSP. The main explanation is that power fluctuations change the pathway of selective reduction processes in selective catalytic reduction (SCR), affecting N₂O selectivity. On-road emission factors indicated declining CO₂ and CH₄ with increased speed, in contrast to N₂O, which presented minimal speed correlation. CH₄ and N₂O collectively constituted 3.86–7.38 % of total equivalent CO₂ emissions, with negligible CH₄ contributions. Consequently, enhancing energy efficiency is pivotal strategies for controlling GHG emissions of China-VI HDDVs. Also, the risk of increased N₂O emissions due to Cu-based zeolite SCR catalyst use must be noted. Regarding durability, engine wear will not significantly increase CO₂ emissions, and the CH₄ emission durability does not require attention. However, the N₂O emission durability necessitates particular attention, given that SCR aging markedly increases N₂O selectivity. Notably, the N₂O emissions from China-VI HDDVs appear to deteriorate linearly with the increased driving mileages, with R² ranging from 0.85 to 0.94, and the emission factors are significantly higher than those of HDDVs equipped with other after-treatment technologies. Environmental protection authorities and catalyst manufacturers must take immediate measures to reduce N₂O emissions and closely monitor the increased N₂O selectivity resulting from SCR catalyst aging.