TABLE 4.1 Potential Percentage Reductions in Fuel Consumption (gallons per mile) for Spark-ignition Vehicles Expected from Advances in Conventional Vehicle Technology by Category, Projected to 2025




Engine and transmission



Weight, drag, and tire loss reduction






Idle stop



NOTE: Values for 2016-2025 include those of 2006-2015. SOURCE: Duleep (2007).

sumption and CO2 emissions. Combining the projections for improvements in engine, transmission, weight, parasitic loss (including friction losses, rolling resistance, and air drag), accessories, and idle-stop components suggests reductions in fuel consumption, relative to today’s vehicle and performance, of 21 to 29 percent (average = 25 percent) by 2015 and 31 to 37 percent (average = 34 percent) by 2025.

Heywood and colleagues at Massachusetts Institute of Technology (MIT) have carried out a series of studies focused on light-duty vehicle fuel efficiency (Heywood, 2007; Kasseris and Heywood, 2007; Kromer and Heywood, 2007). Their studies rely on many of the technologies discussed above but include more aggressive reductions in weight and rolling resistance and aerodynamic drag. Figure 4.3 summarizes the projected fuel consumption improvements for combinations of technology for gasoline- and diesel-powered light-duty vehicles and hybrid electric vehicles

FIGURE 4.3 Fuel consumption of light-duty vehicles with different power trains using projected 2030 technology compared to a typical 2005 gasoline-powered vehicle. NOTE: To convert to gallons per 100 miles, multiply liters per 100 km by 0.426. SOURCE: Heywood (2007).

in 2030 compared to a conventional spark-ignition gasoline engine in a 2005 midsized sedan from Heywood’s work.

The Heywood fuel consumption improvements result from changes in the engine and transmission and include appropriate vehicle weight reductions as well. It is assumed that the improvements are entirely dedicated to reduced fuel consumption. The 2030 spark-ignition gasoline-powered vehicle, with automatic manual transmission and weight reduction included, is projected to have a 38 percent reduction in fuel consumption from the 2005 version of the gasoline vehicle technology. Spark-ignition gasoline-powered vehicles with turbocharger, automatic manual transmission, weight reduction, and parasitic-loss reductions are projected to be capable of a 44 percent reduction in fuel consumption versus today’s spark-ignition gasoline vehicle and an 11 percent improvement over the 2030 spark-ignition gasoline vehicle. Heywood also concludes that CVT technology could reduce fuel consumption further, reaching a 48 percent reduction in fuel consumption compared to today. The turbocharged version of the gasoline vehicle would have an estimated $500 cost premium compared to the 2030 gasoline vehicle.

Also shown in Figure 4.3 is the projected fuel consumption of a 2030 compression-ignition diesel-powered vehicle. The 2030 diesel-powered vehicle, with weight reduction, is projected to have 47 to 50 percent lower fuel consumption than the 2005 spark-ignition gasoline vehicle on a gasoline energy-equivalent basis. It also has a projected 15 percent lower fuel consumption than the 2030 spark-ignition gasoline vehicle on a gasoline energy-equivalent basis. On a fuel volume basis (kilometers per liter of diesel fuel), the 2030 diesel engine shows an additional 15 percent benefit over the 2030 gasoline engine because of the greater energy density of diesel fuel. The diesel-powered vehicle is projected to have a cost premium of about $1,200 over the 2030 gasoline-powered vehicle. If diesels achieved significant market penetration, they could increase the potential reduction in fuel consumption to 3 percent per year. However, the committee was too uncertain of the cost penalty for diesels that meet emission regulations to be willing to include increased penetration in the scenarios of Chapter 6.

Based on the work reviewed above, and assuming a baseline of 25 mpg (miles per gallon) and fuel increases starting in 2010, Duleep’s projections correspond to a 2.3 to 2.9 percent compounding annual reduction in fuel consumption through 2025, or an average of 2.6 percent per year. This results in the average value from Duleep’s analysis, a 34 percent fuel consumption reduction, being applied by 2025. This estimate assumes the diesel improvements discussed above, but the diesel percentage of the fleet remains constant over time. While the data from Heywood suggest that this pace could continue through 2030, the committee judges, based on the discussion in the recent NRC review of the FreedomCar Fuel Partnership (NRC, 2008), that continued weight reductions beyond 2025 would be slower to enter the

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