IS THE GASOLINE GALLON EQUIVALENT AN ACCURATE MEASURE OF MILEAGE FOR ETHANOL AND METHANOL FUEL BLENDS

This study investigated whether or not the gasoline gallon equivalent (GGE), a unit that compares fuel-economy based solely on the fuel energy content, is an accurate measure of the fuel economy of ethanol and methanol fuel blends. Data was collated from several separate reports that tested 2011 flex fuel vehicles (FFV), 2007-2009 vehicles that had their engine control modules (ECMs) optimized to run on alcohol fuels by tuning their software, and a 2012 non-FFV Chevrolet Traverse that was also optimized for alcohol fuels. In all cases no other physical changes were made to the engine or fuel injection system. All alcohol fuel blends in optimized vehicles consistently achieved better miles per gallon than estimated by the GGE. While further testing is needed, these results lead us to believe that the GGE undervalues the fuel economy of alcohol fuels in optimized vehicles even when using existing engine technology. The significance of these findings is that current well-to-wheel emissions models, such as GREET, significantly overstate the emissions and greenhouse gas implications of alcohol fuels compared with well-to-wheel emissions of gasoline.