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Study Finds That Higher Ethanol Blends Result in Improved Energy Efficiency in Flex-Fuel Engines, Partially Offsetting Reduced Energy Density of Fuel

BTU per hp hr at 65 mph for the four ethanol blends. Source: Hanna et al. 2009. Click to enlarge.

A study of flex-fuel vehicles operating on different ethanol blends (E10, E20, E30, and E85) found that higher ethanol blend ratios provide better energy conversion within the engine. The E85 fuel blend consumed fewer BTUs per mile than all other ethanol fuel blends evaluated.

This improved efficiency partially offsets the lower energy density of ethanol (BTUs per gallon), which results in higher fuel consumption. The research was funded in part by the Nebraska Corn Board and through the Hatch Act (University of Nebraska Agricultural Research Division). Additional support for the project was provided by the State of Nebraska Transportation Services Bureau and The Shop, Inc.

While fewer BTUs typically means fewer miles per gallon, energy density is only part of the equation when considering fuel economy. Fuel economy is actually a combination of fuel efficiency and fuel price, and on that point, higher ethanol blends may be the better choice. It just depends on fuel prices at the time. Specific vehicles may test out differently based on engine design and settings, but increased efficiency from ethanol blends make sense, and for the fuel prices we looked at in the study, e85 was the best choice every time.

—Loren Isom, University of Nebraska Industrial Agricultural Products Center

Cost per mile. Source: Hanna et al. 2009. Click to enlarge.

The study tested nine flex-fuel vehicles supplied by the State of Nebraska Transportation Services Bureau vehicle fleet—sedans with 3.0 L and 3.5 L engines and pickups with 4.7 L engines—on a chassis dynamometer.

Three vehicle models were evaluated using three replicate vehicles with similar mileage. The 3.0 L sedans were tested to simulate light-load at vehicle curb weight (vehicle and operator). The 3.5 L sedans and 4.7 L pickups were tested to simulate medium- and heavy-load, respectively, at the gross vehicle weight rating (GVWR) operating on a 1.5% incline.

The vehicles were instrumented to monitor fuel consumption, operating temperatures and emission composition (O2, CO, CO2, NOx, and total unburned hydrocarbons (HC)). Fuel trim (percent adjustment of fuel delivery rates from the manufacturer’s programmed fuel map) and injector pulse width (the amount of time (milliseconds) the fuel injectors are open and allowing fuel to be pumped into the cylinder during the intake cycle) data also were observed from the vehicle computer system using a diagnostics monitor.

The authors summarized their observations, noting that the observations should only be considered representative of the specific vehicles and models evaluated. However, they said, these observations may serve as an indicator for other vehicles/engines that would need to be validated through evaluations of larger data sets. Observations included:

  • The E85 fuel blend provided better energy conversion, lower energy use (BTUs) per mile, than all other fuel blends evaluated.

  • Energy density, BTUs per gallon, decreases as the ethanol concentration increases. As a result, the E85 fuel blend has 26.5% less energy per gallon then the E10 fuel blend, but fuel mileage only decreased 16%, 19%, and 14% for the three models tested.

  • The E85 fuel blend had the lowest fuel costs per mile for the heavy- and lightloaded vehicles and nearly equal costs for the medium-loaded vehicles.

  • The E20 and E30 fuel blends tended to have slightly higher fuel costs per mile other than the use of E30 in the light-load situation, which was slightly lower than the E10 fuel blend.

  • On a horsepower hour basis, more fuel was consumed on a volume basis as the ethanol concentration increased, but the amount of energy (BTUs) consumed per horsepower hour actually decreased with the E85 fuel blend compared to the E10 fuel blend.

  • The maximum horsepower and torque produced by the heavy-loaded, 4.7 L, vehicles tended to increase as the ethanol concentration increased from the E10 to E85 fuel blend. The medium-loaded, 3.5 L, vehicles tended to generate higher horsepower and torque from the E10 to E30 fuel blends. The light-loaded, 3.0 L, vehicles tended to generate higher horsepower and torque from the E10 and E85 fuel blends, but generated slightly less with the E20 and E30 fuel blends.

  • The fuel trim for the heavy-loaded vehicles was very small, a -2.6 to -0.6%. The fuel trim for the light- and medium-loaded vehicles was much larger, ranging from a -9.9% to 26.3%, however the vehicles fuel trim adjusted less when operated on E20 to E30 fuels.

  • Carbon monoxide emissions were detectable with the heavy-loaded, 4.7 L, vehicles, but the level of emissions decreased as the ethanol content of the fuel increased. No carbon monoxide emissions were detectable with the light- and medium-loaded vehicles.

  • From an operational standpoint, the vehicles tended to generate good maximum torque and horsepower at the E20 to E30 blends without giving up much fuel efficiency (mpg), none in the medium-loaded vehicles, while having better average emissions at 65 mph.



Aureon Kwolek

The engines in the vehicles tested were designed for gasoline and then made compatible with ethanol, by upgrading fuel components. This study illustrates that using ethanol in different types of engines/vehicles gives you different results. And that E-85 and mid level blends are feasible fuels, considering ethanol's significantly lower price (in the US) and that 2/3 of the fuel was derived from recycled CO2.

These are not “Ethanol Optimized” engines like the Recardo and Lotus prototypes, which get diesel-like torque and better mileage than gasoline. Ethanol optimized engines are turbocharged with a much higher compression ratio, and they take advantage of the 30% higher octane of ethanol and the faster flame speed and vaporization rate. This also gives you an engine that is upfront cheaper than diesel, lighter and smaller, and burns a cheaper and cleaner domestic fuel – ethanol vs conventional diesel.

Ethanol’s highest use is mixing it 65-35 with water and reforming it onboard into hydrogen. (DonFeng - China).
A 50-50 mix of ethanol-water will combust (MicroFueler - Grid Buster), and ratios as high as 40 ethanol 60 water have been vaporized to run engines.

For all you diesel fans, CleanFlex Power Systems has “a new hydrated-ethanol fuel called EM60 (a mixture of 60% ethanol and 40% water) to combine with diesel fuel to power diesel engines”. (“Ethanol Could Make Diesel Engines Greener”, Zimmerman, Domestic Fuel).



The CleanFlex diesel engine actually ran on 70% diesel fuel and a (20% Ethanol + 10% water mixture). Both the diesel fuel and the E + W mixture are injected separetly.

That combination apparently ran cleaner than pure diesel fuel.

Comparative consumption is not very clearly demonstrated.

CleanFlex is promoting the use of grain based ethanol for the 1 + million diesel ICE operating in USA for the purpose of selling more ethanol.

Wet fuels were never very successful in the past. Car and truck makers dont seem to be very interested.


This is an interesting story. For a long time, some people stated that since ethanol has a lower BTU per gallon number, the mileage would go down accordingly. Some said that the higher octane could be used for more efficiency, but the numbers were not there to support that contention, now they are.

Henry Gibson

It has been well known that the higher octane rating of ethanol could be used for more efficiency in an engine designed for it. The efficiency per gallon and the efficiency per unit available energy are different. This confuses the calculations and perhaps the ethanol blends should be sold as gasoline equivalent gallons; This means bigger gallons delivered so that the prices compare with ease. Methane is sold per gallon of gasoline equivalent.

It is possible to add a lot of water to ethanol and still have the engine run. The Langford Capstone turbine hybrid Ford probably could be modified to run on a VODKA like mixture of half water half ethanol with equal or better energy efficiency than jet fuel. The higher amount of water allows less nitrogen to be in the combustion chamber which reduces the NOX formation. Water and fuel can be injected separatly, but it saves purefication steps and energy to have an alcohol water mix. Gasoline does not mix well with a high water alcohol mix.

The Capstone C30 turbine run on diesel with a small EFFPOWER battery at least and perhaps a small nickel-cadmium battery seems to be a most reliable efficient clean burning automobile model available. A single moving part turbine needs no exhaust treatment to be better than is required and even better combustors can be designed. Any fuel can be used, but it is much cheaper to produce diesel than gasoline. Ethanol does not even add much to the dead weight of the vehicle. The V8 should be dead. ..HG..

Henry Gibson

Sorry folks; if the petroleum industry had financed this study and announced the results they would be more believable.

Never the less, all new vehicles after a certain date should be made to operate on methanol, ethanol, butanol and gasoline of all strengths and mixes.

Methanol from bio-mass should become the next fuel superstar. You might even put in a system that gives the car ten or twenty miles on compressed natural gas or methane produced by bio-decomposition.

The National Geographic reports that 100 units of energy of fossil fuels are used to produce 130 units of energy of ethanol. This seems to be better than some US government reports. There exist some crops that absorb more CO2 than is released by the burning of these 130 energy units of ethanol for the same area that produced enough corn for the ethanol. Corn, itself is such a plant obviously.

Under the present ethanol system more than 230 energy units of CO2 are released into the air for every 130 units of ethanol CO2 energy units used in automobiles. These are only rough figures that ignore the massive amounts of CO2 released by the bacterial decomposition of corn stalks and the use of fermentation byproducts for animal feed. For every pound of ethanol produced by the yeast over a pound of CO2 is produced from the corn sugar fermentation. About two more pounds of CO2 are released when the pound of ethanol is burned.

Considering the CO2 and energy loss during fermentation, and the corn stalks not fermented, and the non digested byproducts of fermentation, an area used to produce this corn ethanol likely will also absorb more than 130 energy units of CO2 if planted with selected trees that need no fossil energy input or human harvesting or care.

This is the case, and so it would be be better to not use 100 units of fossil energy for producing 130 units of corn ethanol, but just use an additional 30 units of fossil fuel with the 100 units for automotive fuel and let the trees absorb at least 130 units of CO2 on the retired corn land and save 100 energy units of CO2 from being released.

I will simplify this for you. From the numbers available to the public, It would much better to find trees or even fast growing cactus plants to grow on the present corn fields than to grow corn for ethanol. The trees or plants grown must have a long life and never be used for fuel, but they only need to absorb a fraction of the CO2 that cultivated corn does to make up for the CO2 produced by just using more fossil fuels for automobiles.

It is likely that producing diesel fuel from coal and turning all corn fields used for ethanol into forests will release much less net CO2 than the production of ethanol fuel or biodiesel.

It could easily reduce net CO2 releases to just even plow the whole corn field crop into a buried tank where chemicals prevent fermentation. Or just turn the whole plant into charcoal with the lowest energy process. ..HG..

Aureon Kwolek

Henry – The claims you’re making are not credible. You’re using really old information for ethanol production. Only about a third of corn ethanol CO2 comes from fossil fuels, and that number is decreasing rapidly with new technology. The other two thirds is recycled CO2 from the corn itself. By 2020, the ethanol industry is likely to be operated entirely on renewables and be carbon neutral or even carbon negative. You are definitely not familiar with the ethanol production technology that is in the works.

Henry, you can dream on, but the corn ethanol industry isn’t going away any time soon. Get ready for ethanol production in the U.S. to double and triple, as we get more corn per acre and more feed per acre. As we utilize the cobs and a portion of the stover and other waste residues to make more ethanol. As we integrate manure-based biogas CHP and algae production into the corn ethanol waste stream. As we develop corn with a sugary stalk that will produce even more ethanol from the entire corn crop - not just from the 1 out of 4 bushels of corn we currently use to produce corn ethanol and distillers grains. No Henry, we’re not going to tear-out our corn crop and plant trees. 75% of it is used to feed livestock and produce food. Get Real.

You advocate mining Coal to make diesel and add more accumulating CO2 to the atmosphere, instead of using a renewable fuel that mostly recycles existing CO2. Do you really think anyone will take you seriously?

Aureon Kwolek

CleanFlex 60-40 ethanol-water is delivered as a vapor through the air intake, and constitutes 15% to 30% of the total fuel consumption – using cheaper, watered-down fuel. This method saves up to $1.20 per hour over conventional diesel, reduces NOx and particle emissions, burns cooler with less heat and friction, increases horse power and efficiency, and is expected to help meet EPA Tier 4 emission standards that go into effect in 2011. (“They Add Ethanol to Diesel” by Greg Lamp)

This has implications. It could be adapted to locomotives, long haul trucks, boats, and any diesel engine. It will have an impact of 15% to 30% of the existing diesel market, and is compatible with a 5% biodiesel blend and possibly higher. This would stimulate domestic ethanol production, reduce imported oil, and reduce the cost of diesel fuel by lowering demand. Lowering the cost of diesel agricultural and shipping fuel will also have a chain reaction across the entire economy, reducing the cost of everything in that path.

The CleanFlex ethanol-water delivery method might also be adapted to light and medium duty gasoline powered cars and trucks, because it bypasses the fuel tank, the fuel line, and the fuel pump - delivered instead as a diluted vapor directly through the air intake.


If lead acid batteries are a bad dream, Nicads are a nightmare.
The mining,and disposal, recycling (or lack of)let alone reliability.
Neither can pass muster.


Doubling or tripling corn ethanol production may have a very positive net effect of the health of the majority of us.

By using 50 + % of corn production to make ethanol, all meat prices will probably double, beef may even triple in price and that could be very positive to treat our growing over-weight problem.

It is well know that much higher food (including junk food) prices may curb obesity. Less obesity = better health at lower cost.

Wouldn't it be amazing if increased corn ethanol production could reduce current extremely high USA health cost, form 17% of GNP to 12% or even 11% like the other industrial nations. Diabetes, most cancers, heart disorders and many other deseases could be reduced by 30% and more.

Of course, by tripling ethanol production, crude importation would drop and so would GHG. USA trade deficits could also be reduced.

Viva grain and corn based ethanol increased production.

richard schumacher

Other than its value as an oxygenating additive, if fuel ethanol doesn't provide a net fossil carbon benefit then it's worse than useless.

These corn agribusiness parasites are almost as bad as the coal industry. Soon they will all need to get real jobs.


Ethanol reduces oil imports, which is THE goal as far as I am concerned. Many of us feel that corn ethanol is not the way to go forward. If we are to get E10/E85 across the U.S. we need to find a better way.



Vehicles + HVAC electrification could meet your goals in a much more acceptable way and with more finesse, especially if done concurrently with the introduction of more wind-solar-nulear-geothermal power plants.

Agrofuels may be ok as long as the world has food surpluses, but that is not the case and may never happened. Secondly, most liquid fuels create more GHG than we can manage and perpetuate the use of obsolete technologies.

I my humble opinion, using more resources to develop and transition to new sustainable technologies may be a better idea than trying to patch up the existing inefficent ones.


Putting aside the entire GHG argument as it has lost merit - there is a huge growth in ethanol from all sources on its way. And this will only benefit the national energy use profile. Efficiencies in production of corn increase yield and the use of cellulosic waste improve on that.

we need a liquid fuel and alcohol from waste and biomass is the best process near term. Next will be adoption of algal oil grown on waste land and in brackish water. Until algal biodiesal is ramped up - alcohol will meet our liquid energy needs, especially for heavy lifting transport.

Aureon Kwolek

The doubling and tripling of ethanol production is not going to come from increased corn acreage, or at the expense of using more livestock feed. There is a dramatic revolution of advanced biofuel technology in the works:

Ethanol now being made from landfill trash, food waste, agricultural residues, forestry waste, etc. Mitigated manure-based CHP now producing surplus electric power and waste heat for distillation at ethanol refineries - replacing coal and natural gas for production power. Corn cobs and part of the stover now being made into several hundred gallons per acre of addition ethanol - that redistributes the production inputs. Farmers who now make their own biofuels from ethanol or oil they produced themselves – using biofuels to produce biofuels (instead of using fossil fuels). Hybrid electric tractors being developed. A jump in corn crop yield from 150 up to 162 bushels per acre in just the past 2 years, and future PER ACRE corn yield expected to double by 2030 – without planting additional acreage. Development of a sugary corn stalk that will produce several hundred gallons of additional ethanol per acre - from the entire corn crop, not just the 25% corn ethanol sector. The increase of sweet sorghum as an alternative feedstock to corn. Sewage sludge now being developed as a viable ethanol feedstock. 100 ton plus per acre Algae and Duckweed now being grown on the corn ethanol waste stream and other waste streams – the future blockbuster feedstock for both ethanol and biodiesel. Biomass gasification now producing electric power or 90 to 135 gallons of ethanol or synthetic fuels from a ton of biomass, depending on the feedstock and the process. Biofuels being produced and consumed locally - delivered directly to local retail blender pumps, bypassing the existing centralization of petroleum. And the list goes on.

Ethanol diluted with 35% or more water: And either being reformed onboard into hydrogen on demand as a primary fuel. Or being vaporized and delivered through the air intake - to supplement 15 to 30% of conventional gasoline and diesel fuels. Supplemental Ethanol-Water in combination with “PulseStar” Plasma Spark Plugs.


The flex fuel car tested tested by Consumer reports got 27% worse mileage on E-85, not that 16% is a good thing.


Wonder why the Nebraska Corn Board is studying fuel? You can bet your first born that the study is biased.

A recent study in Nature suggests that corn ethanol is a dead end because industrial agriculture and fossil fuels are the two drivers that have caused us to cross three out of nine planetary thresholds. I think the article can be viewed if you don't have a subscription.


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