• Adopting the full combination of improved technologies in medium and large cars and pickup trucks with spark-ignition engines could reduce fuel consumption by 29% at an additional cost of $2,200 to the consumer.

• Replacing spark-ignition engines with diesel engines and components would yield fuel savings of about 37% at an added cost of approximately $5,900 per vehicle.

• Replacing spark-ignition engines with hybrid engines and components would reduce fuel consumption by 43% at an increase of $6,000 per vehicle.

The committee’s estimates are based on a variety of factors including recent reports from regulatory agencies and other sources; component cost estimates from suppliers; discussions with experts; and comparisons of prices and fuel consumption of similar vehicles.

Estimated price increases are based on current economic conditions and the concept of “incremental retail price equivalent (RPE) cost,” which represents the average additional price consumers would pay for a fuel economy technology.

Engines and Technologies

Spark-ignition engines—which will continue to be the dominant type of engine in the US for the next 10 to 15 years—have seen many technology improvements that are producing significant fuel savings. As a result, automobile manufacturers are able to create packages of technologies that can meet cost and effectiveness targets in small, incremental steps.

For example, the report notes the promise of cylinder deactivation, turbocharging and downsizing. Deactivation can reduce fuel consumption by as much as 10% at a retail vehicle price increase of $350 to $500, the report says. The committee estimated costs for turbocharging and downsizing to range from close to zero, when converting from a V6 to a four cylinder engine, to almost $1,000 when converting from a V8 to a V6.

Valve event modulation can also reduce fuel consumption and cause a slight increase in performance, the report said.

Variable compression ratio, camless valve trains, and homogeneous-charge compression ignition were all given careful consideration during the course of this study. Because of questionable benefits, major implementation issues, or uncertain costs, it is uncertain whether any of these technologies will have any significant market penetration in the next 10 to 15 years.

—“Assessment of Technologies”

Diesel engines may become more popular in the United States now that new emission control technologies are allowing for a wide range of diesel engines to meet federal and state air quality standards, the report says. Replacing a 2007 model spark-ignition engine with a base-level CI diesel engine—including a six-speed dual clutch transmission and other efficiencies—could reduce fuel consumption by about 33%, and with an RPE of about $4,800 for a six-cylinder engine.

Advanced CI diesel engines, expected to reach the market in the next five years, could reduce fuel consumption an additional 7% to 13%, with estimated vehicle RPE cost of about $4,600 for small passenger cars to $5,900 for intermediate or larger vehicles.

Hybrid vehicle technologies are one of the most active areas of research and development. The degree of hybridization can vary from minor vehicle stop-start systems to complete vehicle redesign. A fully hybrid vehicle could reduce fuel consumption by about 50% at an estimated price increase of up to $9,000 a vehicle depending on vehicle size. The report notes that a significant part of reducing fuel consumption in full hybrids results from complete vehicle redesign that incorporates low-rolling-resistance tires, improved aerodynamics, and smaller, more efficient spark-ignition engines.

Hybrid vehicle improvements in the next 10 to 15 years will occur primarily in reducing costs of hybrid power train components and improving battery performance, the report said. While many challenges remain in developing lithium-ion battery technology, small, limited-range battery electric vehicles will be on the market in the next decade, the committee predicted.

During the past decade, significant advances have been made in lithium-ion battery technology. When the cost and safety issues associated with them are resolved, lithium-ion batteries will replace nickel-metal-hydride batteries in hybrid electric vehicles and plug-in hybrid electric vehicles. A number of different lithium-ion chemistries are being studied, and it is not yet clear which ones will prove the most beneficial. Given the high level of activity in lithium-ion battery development, plug-in hybrid electric vehicles will be commercially viable and will soon enter at least limited production.

The practicality of full-performance battery electric vehicles (i.e., with driving range, trunk space, volume and acceleration comparable to those of vehicles powered with internal-combustion engines) depends on a battery cost breakthrough that the committee does not anticipate within the time horizon considered in this study. However, it is clear that small, limited-range, but otherwise full-performance battery electric vehicles will be marketed within that time frame.

Although there has been significant progress in fuel cell technology, it is the committee’s opinion that fuel cell vehicles will not represent a significant fraction of on-road light-duty vehicles within the next 15 years.

—“Assessment of Technologies”

The report also examines a range of non-engine vehicle technologies. Relatively minor changes that do not involve re-engineering the vehicle or require recertification for fuel economy, emissions, or safety can be implemented within the next several years. They include reducing vehicle mass by using lighter materials, improving aerodynamics, or switching to low-rolling-resistance tires. Two important areas of research for long-range improvements include transmission systems and light-weighting – making vehicles very light with new materials under development.

The report focuses on fuel consumption because energy savings are directly related to the amount of fuel used. In contrast, fuel economy measures how far a vehicle will travel with a gallon of fuel. Because fuel consumption data indicate money saved on fuel purchases and reductions in carbon dioxide emissions, vehicle stickers should provide consumers with fuel consumption data in addition to fuel economy information, the report says.

Also, the National Highway Traffic and Safety Administration and the US Environmental Protection Agency should review and revise fuel economy test procedures so they better reflect vehicle operating conditions and provide incentives to manufacturers to reduce fuel consumption. The report identifies an improved method that NHTSA and EPA should use to more accurately estimate a technology’s ability to reduce fuel consumption.

The committee was not charged with determining how long it would take for money saved on fuel purchases to offset higher vehicle prices; this analysis will be conducted by regulatory agencies as they develop standards for light-duty vehicle fuel economy and greenhouse gas emissions.

The study was sponsored by the National Highway Traffic Safety Administration. The National Academy of Sciences, National Academy of Engineering, Institute of Medicine, and National Research Council make up the National Academies. They are private, nonprofit institutions that provide science, technology, and health policy advice under a congressional charter. The Research Council is the principal operating agency of the National Academy of Sciences and the National Academy of Engineering.

Resources

• Assessment of Fuel Economy Technologies for Light-Duty Vehicles