How does ethanol's energy density compare to gasoline, and what are the implications for vehicle efficiency?

• A. Ethanol Has About 60-70 Percent of Gasoline's Energy Per Unit Volume; Leads to Reduced Fuel Economy Unless Optimized.
• B. Ethanol Has Higher Energy Density Than Gasoline.
• C. Ethanol Has the Same Energy Density as Gasoline.
• D. Ethanol Energy Density Is Negligible.

Answer: (A)

The key idea is energy density by volume and how that affects fuel economy. Ethanol stores less energy per unit volume than gasoline—roughly about 60–70% as much energy per gallon. So, using ethanol in a standard engine means less energy is available per mile driven, leading to lower miles-per-gallon unless the engine and fuel system are specially designed or calibrated to take advantage of ethanol’s properties. Ethanol does have a higher octane rating, which can enable higher compression or other optimizations that improve efficiency, but those benefits only materialize if the engine is optimized for ethanol. In typical vehicles not tuned for ethanol, the lower energy density is the dominant factor, resulting in reduced fuel economy.