The technology assessments conducted by the Environmental Protection Agency and the National Highway Traffic Safety Administration to inform the 2017–2025 passenger vehicle fuel economy and greenhouse gas emissions regulations were conducted five years ago. Since then, innovations in vehicle technologies have come rapidly, enabled by computer-aided design tools and electronic engine controls.
The naturally aspirated gasoline engine is the long-established workhorse of passenger vehicle power trains. Innovative designs to improve fuel efficiency—such as four-valve engines, cylinder deactivation, variable valve timing and lift, gasoline direct injection, and stop-start systems—have helped this relatively low-cost "conventional" technology maintain its dominance of the U.S. passenger vehicle market. However, gasoline turbocharged engines are rapidly increasing market share, and the agencies projected they would almost completely replace naturally aspirated engines by 2025. This analysis of recent trends in costs, fuel-efficiency gains, and market penetration suggests that naturally aspirated engines may play a larger role in the U.S. vehicle fleet than the EPA and NHTSA projected, thanks to innovative technologies such as high-compression engines with cooled exhaust gas recirculation, improved stop-start systems, and dynamic cylinder deactivation.
This paper is one of a series that the ICCT, in collaboration with automotive suppliers, is undertaking to profile and evaluate technological developments in engines, transmissions, vehicle body design and lightweighting, and other measures. Each paper in the series will assess:
- How current costs, benefits, market penetration compare to projections that were made for the rulemaking
- Recent technology developments that were not considered in the rulemaking and how they impact cost and benefits
- Customer acceptance issues, such as real-world fuel economy, performance, drivability, reliability, and safety