|Highway fuel economy improvement, E20 and E30 vs. Tier 2 gasoline. Click to enlarge.|
Research findings released today indicate that mid-range ethanol blends—fuel mixtures with more ethanol than 10% (E10) but less than 85% (E85)—can in some cases provide better fuel economy than regular unleaded gasoline, even in standard, non-flex-fuel vehicles. The new study, co-sponsored by the US Department of Energy and the American Coalition for Ethanol (ACE), also found that mid-range ethanol blends reduce harmful tailpipe emissions.
Previous assumptions held that ethanol’s lower energy content directly correlates with lower fuel economy for drivers. Those assumptions were found to be incorrect. Instead, the new research suggests that there is an optimal blend level of ethanol and gasoline—most likely E20 or E30—at which cars will get better mileage than predicted based strictly on the fuel’s per-gallon Btu content. The optimal blend varies with the vehicle, according to the findings.
The University of North Dakota Energy & Environmental Research Center (EERC) and the Minnesota Center for Automotive Research (MnCAR) conducted the research using four 2007 model vehicles: a Toyota Camry, a Ford Fusion and two Chevrolet Impalas, one flex-fuel and one non-flex-fuel.
Researchers used the EPA Highway Fuel Economy Test (HWFET) to examine a range of ethanol-gasoline blends from straight Tier 2 gasoline up to 85 percent ethanol. All of the vehicles got better mileage with ethanol blends than the ethanol’s energy content would predict, and three out of four actually traveled farther on a mid-level ethanol blend than on unleaded gasoline.
In addition to the favorable fuel economy findings, the research provides strong evidence that standard, non-flex-fuel vehicles can operate on ethanol blends beyond E10. The three non-flex-fuel vehicles tested operated on levels as high as E65 before any engine fault codes were displayed. Emissions results for the ethanol blends were favorable for nitrogen oxides, carbon monoxide and non-methane organic gases, showing an especially significant reduction in CO2 emissions for each vehicle’s optimal ethanol blend (E20 for the flex-fuel Chevy, E30 for the Toyota and Ford, E40 for the non-flex Chevy).
Ethanol’s energy content was not found to be a direct predictor of fuel economy. All four vehicles tested exhibited better fuel economy with the ethanol blends than the Btu-value estimates predicted.
E20 and E30 ethanol blends outperformed unleaded gasoline in fuel economy tests for certain autos. Contrary to Btu-based estimates of fuel economy for ethanol blends, three of the four vehicles tested achieved their highest fuel efficiency not on gasoline, but on an ethanol blend. Mid-level blends of ethanol E20 (20% ethanol, 80% gasoline) and E30 (30% ethanol, 70% gasoline) offered the best fuel economy in these tests.
E30 offered better fuel economy than gasoline (a 1% increase) in both the Toyota and the Ford.
E20 offered better fuel economy than gasoline (a 15% increase) in the flex-fuel Chevrolet.
The non-flex-fuel Chevrolet more closely followed the Btu-calculated trend for fuel economy, but did experience a significant improvement over the trend line with E40 (40% ethanol, 60% gasoline), indicating that this may be the optimal ethanol blend level for this vehicle.
The standard, non-flex-fuel vehicles operated well on ethanol blends beyond 10%. The Ford Fusion operated on E45, the Toyota on E65, and the non-flex-fuel Chevy on E55. No engine fault codes were displayed until these levels were surpassed.