Johnson, T. and Joshi, A., "Review of Vehicle Engine Efficiency and Emissions," SAE Technical Paper 2017-01-0907, 2017, doi:10.4271/2017-01-0907.
This review paper summarizes major and representative developments in vehicle engine efficiency and emissions regulations and technologies from 2016. The paper starts with the key regulatory developments in the field, including newly proposed European RDE (real driving emissions) particle number regulations, and Euro 6 type regulations for China and India in the 2020 timeframe. China will be tightening 30-40% relative to Euro 6 in 2023. The California heavy duty (HD) low-NOx regulation is advancing and the US EPA is anticipating developing a harmonized proposal for implementation in 2023+. The US also finalized the next round of HD GHG (greenhouse gas) regulations for 2021-27, requiring 5% engine CO2 reductions. 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. Several LD gasoline concepts are achieving 10-15% and some up to 35% reductions relative to GDI (gasoline direct injection) engines of today. 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 unique proposals are proposed for reaching 55% BTE. Lean NOx control technologies are summarized, including SCR (selective catalytic reduction), SCR filters, and combination systems. Emphasis is on durability, and greatly reduced emissions. Diesel PM (particulate matter) reductions are evolving around soot regeneration for both standard DPFs (diesel particulate filters) and SCR filters. Research oxidation catalysts are oxidizing propane and CO, and methane at 225-250°C. Gasoline particulates are a major topic in emissions control. The paper provides a broad overview of various factors that can impact emissions. Gasoline particulate filter durability and ash loading is better understood. Finally, the paper discusses some key developments in three-way catalysts, with improved understanding of lower-cost catalysts and system considerations. Advances in lean-burn gasoline emissions control from a few labs are also summarized.