Review of Vehicle Engine Efficiency and Emissions

This review article summarizes major and representative developments in vehicle emissions regulations, engine efficiency, and emission control from 2017. The article starts with the key regulatory developments in the field, including newly proposed European light-duty (LD) CO₂ regulations (15 and 30% cuts in 2025 and 2030, respectively, from 2020 levels) and technical improvements of the Euro 6 real driving emissions (RDE) regulations. China finalized their new energy vehicle (NEV) mandates for 2019 and 2020. LD and heavy-duty (HD) engine technology continues showing marked improvements in engine efficiency. Key developments are summarized for gasoline and diesel engines to meet both the emerging criteria and greenhouse gas (GHG) regulations. Several LD gasoline concepts are achieving 10-15% and some up to 35% reductions relative to gasoline direct injection (GDI) engines of today. Projections indicate tight CO₂ regulations will require some degree of hybridization and/or high-performing gasoline and diesel engines. Scoping work on HD engines is reported on achieving 55% break thermal efficiency (BTE) using methods that can reasonably be commercialized. Lean NOx control technologies are summarized, including selective catalytic reduction (SCR), NOx adsorbers, and systems. Fundamentals of the SCR reaction are explored at the atomistic level. Diesel particulate filter (DPF) work has been focused on structure-performance relationships and ash behavior. Research oxidation catalysts are approaching 90% efficiency for hydrocarbon (HC) and CO oxidation at 160-190 °C. Gasoline particulates are a major topic in emission control. The article provides a broad overview of various factors that can impact emissions. The impact of fuel composition and application is summarized. Gasoline particulate filter (GPF) durability and ash loading are better understood. Finally, the article discusses some key developments in three-way catalysts, with improved understanding of low-temperature performance. Advances in lean-burn gasoline emission control from a few labs are also summarized.