Fuel Economy

All vehicles have a fuel economy (measured as miles per US gallon -MPG-, or liters per 100 km) that is directly proportional to energy content. Ethanol contains approx. 34 % less energy per unit volume than gasoline and therefore will result in a 34 % reduction in miles per US gallon. For E10, the effect is small (~3 %) when compared to conventional gasoline and even smaller (1-2 %) when compared to oxygenated and reformulated blends. However, for E85, the effect becomes sig­nificant. E85 will produce lower mileage than gasoline and will require more frequent refueling. Actual performance may vary depending on the vehicle. This reduced fuel economy should be considered when making price comparisons. For example, if regular gasoline costs $3.00 per gallon, and E85 costs $2.19 per gal­lon, the prices are essentially equivalent. If the discount for E85 is less than 27 %, it actually costs more per mile to use.

Research is underway to increase fuel efficiency by optimizing engines for ethanol-based fuels. Ethanol’s higher octane allows an increase of an engine’s compression ratio for increased thermal efficiency. In one study, complex engine controls and increased exhaust gas recirculation allowed a compression ratio of 19.5 with fuels ranging from neat ethanol to E50. Thermal efficiency up to approximately that for a diesel was achieved. This would result in the miles per gallon of a dedicated ethanol vehicle to be about the same as one burning gasoline. There are currently no commercially available vehicles that make significant use of ethanol-optimizing technologies, but this may change in the future.


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