U.S. Department of Energy - Energy Efficiency and Renewable Energy
Vehicle Technologies Office
Maximizing Alternative Fuel Vehicle Efficiency
Besides their energy security and environmental benefits, many alternative fuels such as biodiesel, ethanol, and natural gas have unique chemical properties that offer advantages to drivers. These properties can include higher octane ratings and cetane numbers than conventional petroleum-based fuels, which can help an engine run more smoothly. However, most alternative fuel vehicle engines are not designed specifically for these fuels. Instead, these engines are originally optimized to use petroleum-based fuels and then adapted to tolerate the use of alternative fuels. The Vehicle Technologies Office supports research to design engines optimized for alternative fuels that can exploit their unique properties and increase these vehicles' efficiency.
This distinction is particularly important for flexible fuel vehicles that can run on E85 (up to E85 percent ethanol). Although more than two million drivers bought flexible fuel vehicles in the U.S. in 2012, very few of them use E85. In general, flexible fuel vehicles running on E85 are very similar to those running on gasoline; they have comparable performance, speed, and acceleration. However, because a gallon of ethanol inherently has less energy than a gallon of gasoline, flexible fuel vehicles have a 27 percent lower fuel economy running on E85. Fortunately, designing flexible fuel vehicles to run specifically on E85 rather than gasoline can help close that gap. To reduce this disparity, the Vehicle Technologies Office is supporting research to develop engines with advanced controls and combustion systems for the next generation of flexible fuel vehicles. These more efficient engines should lower the cost of driving on E85, encouraging more flexible fuel vehicle owners to use it.