E85 is nominally 85% ethanol and 15% gasoline. The exact percentages of ethanol content (vol %) actually range from 68% to 83%, as determined in the specifications for E85 found in ASTM-D5798. Each geographical region of the country is assigned an appropriate fuel class rating, ranging from 1 to 3, depending on the climate for a given month. As of the revisions approved on Dec. 1, 2010, the main variable between classes is the allowable vapor pressure range. Before these revisions, allowable ethanol levels also varied upon class, as noted in Table 1 under the “Previous Ethanol Content, Vol %” column. The classifications are as follows:
|Fuel Class||Allowable minimum ambient temperatures (degrees F)||Previous allowable ethanol content (vol %)||Current allowable ethanol content (vol %)||Vapor pressure (psi)|
|Class 3||< 23||70-83||68-83||9.5-12.0|
Fuel classes can also be described as “summer blend” and “winter blend”. “Summer blend” refers to a high ethanol content at or just below 83%, corresponding to the previous (pre-December 2010 revisions) Class 1 specifications, while “winter blend” refers to a lower ethanol content of about 70%, corresponding to the historic Class 3 specifications. The lower ethanol percentage in the winter is meant to address problems starting vehicles in colder climates. Beyond the specified guidelines, the actual blend is determined by the distributor and vendor. In a study conducted by the Coordinating Research Council, Inc. (CRC), it was found that most of the samples were off-specification from ASTM-D5798, indicating a need to address quality control in E85.
Because ethanol content varies from season to season, region to region, and distributor to distributor, it is helpful to have an estimate for the annual average ethanol content percentage. In the Annual Energy Outlook Report 2011, an annual average of 74% ethanol, 26% gasoline is used for forecasting purposes.