Ethanol can be combined with gasoline in blends ranging from E10 (10% or less ethanol, 90% gasoline) up to E85 (up to 85% ethanol, 15% gasoline), with those in-between being called "intermediate blends." The U.S. Environmental Protection Agency's Renewable Fuels Standard (under the Energy Policy Act of 2005 and the Energy Security and Independence Act of 2007) requires the country use as much as 36 billion gallons of renewable fuels annually by 2022, most of which will be ethanol. However, current ethanol usage is much lower than the requirements. It would be challenging to increase this use substantially under current conditions, as E85 fueling infrastructure is limited and most gasoline already includes 10 percent ethanol (this is often referred to as the "blend wall"). To meet future requirements, conventional (non-flexible fuel) vehicles may need to use intermediate blends of ethanol, such as E15 or E20.
Before it could allow conventional vehicles to use intermediate blends, the federal government had to determine what effects these fuels could have on vehicles’ performance and emissions. The Clean Air Act requires that vehicles and engines using a fuel or fuel additive will continue to meet their emission standards over their “full useful life.” The Vehicle Technologies Office supported work to examine the impact of E15 through E20 on passenger vehicles, outdoor equipment and generator sets. This research documented the effects of these fuels on the vehicles’ and equipment’s tailpipe emissions, fuel economy, emissions systems, and drivability. This research is documented in a number of reports from the national laboratories. The data on "Fueling Infrastructure Polymer Materials Compatibility to Ethanol-blended Gasoline" is available on OpenEI.
Based on this research, the U.S. Environmental Protection Agency issued waivers allowing vehicles from model year 2001 and beyond to use E15 in 2010 and 2011. The limit for vehicles before the 2001 model year and other engines and vehicles that use blends up to 10 percent ethanol remains, such as lawn mowers, motorcycles, and boats.
VTO’s research effort on E15 testing in vehicles has concluded. EPA did not approve the use of E15 in marine engines, so VTO is currently investigating the use of other alternative fuels such as butanol that may be more compatible with non-automotive engines.