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US Motor Vehicle Technology

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Motor Vehicle Fleet composition and turnover

In 2007, the United States had approximately 136 million automobiles and an additional 100 million trucks and buses in operation.[1] Of this fleet, approximately 634,000, or 0.25%, used or could use fuels other than standard motor vehicle gasoline or diesel fuel.[2]

The vehicle fleet is replaced very slowly. Fleet turnover estimates suggest that only 4.5% of these vehicles are scrapped each year, and that the median vehicle age is 9 years. Increases in vehicle quality and durability have lowered the scrappage rate and increased median vehicle age for the last decade.[3]

Biofuel compatibility and infrastructure

Biofuels face some compatability issues with cars currently on the road. These issues differ depending on the chemical composition of the fuel and the manufacturing method.

Ethanol compatibility

Ethanol-based fuels are more corrosive and have a higher octane than standard fuels. They therefore are incompatible with most internal combustion engines designed to use gasoline or diesel fuel. Special engines designed to burn both gasoline and high-percentage-ethanol mixes like E85 are available from a number of manufacturers including General Motors and Ford Motor Company. The latest available official statistics show that approximately 300,000 E85 vehicles were in use, making them the most popular alternative-fueled vehicle.

Biodiesel compatibility

Biodiesels made from either syn-gas or natural oils without upgrading are corrosive and unstable, making their use in standard diesel engines problematic. If upgrading is used, biodiesels from these sources can be used in standard diesel engines. Some studies suggest that use of either standard biodiesel blends or a mixture of biodiesel and petroleum diesel can improve engine performance.[4]

Greenhouse gas footprint

Transportation generates approximately 34% of all United States emissions of carbon dioxide.[5] The motor vehicle fleet is estimated to account for approximately 59% of this, or 20% of total U.S. emissions.[6]

Biofuels may provide a means to reduce the greenhouse gas footprint of the transportation sector. To estimate the size of potential reductions, it is now common to use a lifecycle assessment method. Lifecycle methods suggest that some amount of reduction is possible for cellulosic fuels, but the level of reduction has not been conclusively established. Farrel et al[7] conclude that cellulosic ethanol could be produced and used in ways up to 25% more efficient in greenhouse gas terms than gasoline. However, corn-based ethanol offers little improvement. Wu et al[8] find that switchgrass-derived transportation fuels could offer an 85% reduction in greenhouse gas emissions on a lifecycle basis compared to gasoline.

References

  1. ↑ Highway Statistics 2007 (Washington, DC: Federal Highway Administration, 2007), table MV-1: State Motor Vehicle Registrations, at [1]. Accessed 6 January 2009.
  2. ↑ Annual Energy Review 2007 (Washington, DC: Energy Information Administration, 2007), table 10.4:: Estimated Number of Alternative-Fueled Vehicles in Use and Fuel Consumption, 1992-2006, at [2]. Accessed 6 January 2009.
  3. ↑ "R.L. Polk Reports Vehicle Age in U.S. on the Rise", Reuters News Service, 20 February 2008, available at [3]. Accessed 6 January 2009.
  4. ↑ George W. Huber, Sara Iborra, and Avelino Corma, "Synthesis of Transportation Fuels from Biomass: Chemistry, Catalysts, and Engineering", Chem. Rev. 106(9) 2006
  5. ↑ Data for 2007, from "Emissions of Greenhouse Gas Report", report # DOE/EIA-0573(2007) (Washington, DC: Energy Information Agency, 2007), table 6. At [4]. Accessed 6 January 2009.
  6. ↑ "Emissions of Greenhouse Gas Report", table 10, at [5].
  7. ↑ Alexander E. Farrell, Richard J. Plevin, Brian T. Turner, Andrew D. Jones, Michael O'Hare, Daniel M. Kammen, "Ethanol Can Contribute to Energy and Environmental Goals", Science 311(5760) 2008.
  8. ↑ May Wu, Ye Wu, and Michael Wang, "Energy and Emission Benefits of Alternative Transportation Fuels Derived from Switchgrass: A Fuel Lifecycle Assessment" Biotechnology Progress 22(4) 2006, p1012.
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