Johnson, T., "Vehicular Emissions in Review," SAE Int. J. Engines 9(2):1258-1275, 2016, doi:10.4271/2016-01-0919.
This review paper summarizes major and representative developments in vehicular emissions regulations and technologies from 2015. The paper starts with the key regulatory advancements in the field, including newly proposed Euro 6 type regulations for Beijing, China, and India in the 2017-20 timeframe. Europe is continuing developments towards real driving emissions (RDE) standards with the conformity factors for light-duty diesel NOx ramping down to 1.5X by 2021. The California heavy duty (HD) low-NOx regulation is advancing and may be proposed in 2017/18 for implementation in 2023+.LD (light duty) and 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 regulations. LD gasoline concepts are achieving 45% BTE (brake thermal efficiency or net amount of fuel energy gong to the crankshaft) and closing the gap with diesel. Projections indicate tight CO2 regulations will require some degree of hybridization and/or high-performing diesel engines. HD engines are demonstrating more than 50% (BTE) using methods that can reasonably be commercialized; and proposals are developed for reaching 55% BTE.Lean NOx control technologies are summarized, including SCR (selective catalytic reduction), SCR filters, and combination systems. Emphasis is on durability, N2O, and greatly reduced emissions. Diesel PM (particulate matter) reductions are evolving around the nature of soot and the distribution in the filters. Gasoline direct injection (GDI) particulates carry PAHs (polycyclic aromatic hydrocarbons) through the three way catalyst, but filters can remove most of them. Gasoline particulate filter regeneration is now better understood. Improved understanding of oxidation catalyst formulations are reported with further quantification of the impact of precious metal formulations. Finally, the paper discusses some key developments in three-way catalysts, with improved understanding of the catalyst-support interactions, and the introduction of a low-mass cellular substrate that improves TWC cold start performance.