Understanding System- and Component-Level N ₂ O Emissions from a Vanadium-Based Nonroad Diesel Aftertreatment System 2017-01-0987

Nitrous oxide (N₂O), with a global warming potential (GWP) of 297 and an average atmospheric residence time of over 100 years, is an important greenhouse gas (GHG). In recognition of this, N₂O emissions from on-highway medium- and heavy-duty diesel engines were recently regulated by the US Environmental Protection Agency (EPA) and National Highway Traffic Safety Administration’s (NHTSA) GHG Emission Standards. Unlike NO and NO₂, collectively referred to as NO_x, N₂O is not a major byproduct of diesel combustion. However, N₂O can be formed as a result of unselective catalytic reactions in diesel aftertreatment systems, and the mitigation of this unintended N₂O formation is a topic of active research. In this study, a nonroad Tier 4 Final/Stage IV engine was equipped with a vanadium-based selective catalytic reduction (SCR) aftertreatment system. Experiments were conducted over nonroad steady and both cold and hot transient cycles (NRSC and NRTC, respectively). Engine-based results show that N₂O emissions for this nonroad engine and aftertreatment system are below the current 0.1 g/bhp·hr on-highway GHG standard. To better understand the processes which contribute to the system-level N₂O emissions seen during engine testing, reactor-based experiments were conducted to elucidate the fundamental component-level mechanisms responsible for N₂O formation. This study provides significant system- and component-level insights into the formation of N₂O in diesel aftertreatment systems.