Working Paper

Downsized, boosted gasoline engines

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.

Although turbocharging is not penetrating the fleet as rapidly as predicted by the rulemaking, there have been significant cost reductions in turbocharging and related components since the rulemaking. 48V hybrids are also significantly cheaper than the 110V BAS system assessed by the agencies in the rule. More importantly, even though it has been only 5 years since the rulemaking technology assessments, there are major efficiency developments already in production that were not anticipated or included in the rulemaking: Miller cycle, e-boost, and variable geometry turbochargers (for gasoline engines). Another major development will be in production by 2018: variable compression ratio.

The costs of e-boost are higher than Miller cycle, but there are excellent synergies between e-boost and both Miller cycle and 48V hybrid systems. Overall, e-boost + 48V hybrid systems are expected to provide more than half of the benefits of a full hybrid system at less than half the cost, or a cost of $800–$1,400. They would also enable Miller cycle at no additional cost, resulting in roughly 20-25% reduction in fuel consumption at less than $1,400 compared to the agencies’ turbocharger estimates in the rulemaking, or roughly $35-$70 per percent fuel consumption reduction.

This paper is the third in 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 assesses:

  • 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