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By Robert Rapier on Mar 7, 2009 with 3 responses

Fuel Efficiency of Ethanol in the Real World

There is a particular poster at The Oil Drum who frequently claims that a gallon of ethanol can replace a gallon of gasoline in a car. Although he denies it, his over-the-top defenses of corn ethanol are consistent with someone who is being paid to promote it. There is no objectivity on his part, ever. A good ethanol study is one in which the results are pro-ethanol, even if it is funded by the ethanol industry. A questionable study is one in which the results are anti-ethanol – regardless of who funded it or where it was published. It doesn’t matter if a study was done as a high school science project if he likes the results. On the other hand, he has rejected a peer-reviewed paper in Science because he didn’t like the conclusions.

Here he is making his fuel efficiency claims:

Ethanol has an Octane Rating of 113 AKI (compared to 86 for straight gasoline.) This means that even though it’s “energy content” is lower, it can achieve much greater Efficiency than gasoline when burned in a proper engine.

That’s why recent tests, such as the one performed by N.Dakota Univ, and Mn State, show that, when burned in newer vehicles, E20 gave slightly better mileage than straight gasoline in three of four cars tested.

Later in that post he wrote: “…it has been show that one gallon of ethanol can, in a newer engine, for all practical purposes, replace one gallon of gasoline (116,000 btus,)…

Here is the study he used to support his point:


The funny thing is that the tests with ethanol blends actually showed a loss of fuel efficiency on 72% of the trials, even though the test was sponsored by the American Coalition of Ethanol. This is comical considering that this particular person won’t accept any study remotely having any ties to oil companies. As I explained, here was what the test actually showed:

Without a doubt, you are embellishing the results. This is what I see from the ethanol tests. Look at Figures 10-13. Here is the reality of the tests:

Figure 10. 2007 Toyota Camry, 2.4-L engine – 6 of 7 tests show worse fuel efficiency on an ethanol blend. There is one apparent outlier, which was the basis for the claims. (And it looks like a classic outlier, with almost all of the other points falling as predicted).

Figure 11. 2007 Chevrolet Impala (non-flex fuel), 3.5-L engine – 5 of 5 tests show worse fuel efficiency on an ethanol blend.

Figure 12. 2007 Chevrolet Impala (flex fuel), 3.5-L engine – 8 tests, 2 show better fuel efficiency, 2 show the same, and 3 show worse fuel efficiency on an ethanol blend.

Figure 13. 2007 Ford Fusion, 2.3-L engine – 4 of 5 tests show worse fuel efficiency on an ethanol blend. There is one apparent outlier.

So, what can we conclude? Of 25 data points, 18 confirm that the fuel economy is worse on an ethanol blend. That is 72% of the tests, and these tests were paid for by the ethanol lobby (which is why I suspect the results were spun as they were). The outliers are interesting enough for further investigation, but you have vastly overstated the test results. In reality, if you pulled the results out of a bag, you have only a 28% chance of improving your fuel efficiency on the basis of any particular test. Further, the outlier didn’t always occur at the same percentage, which would be quite problematic even if the result is confirmed.

Apparently for you, this is like pass/fail. If we have 4 data sets, and in each set 1 of 10 points showed a positive result, you claim 100% positive results. I won’t say that’s dishonest, but it is definitely putting the best possible spin on the situation. And while it seems that the matter is settled for you, what I would do as a next step is hone in on those outliers and see if they can be consistently replicated. Unless they are, you may be banking your claims on nothing more than experimental error, as the tests showing the desired result were in the minority.

That hasn’t stopped this person from continuing to argue that we should go to higher ethanol blends, since this study shows the benefit. Of course there have been plenty of (objective) tests that do show the expected drop in fuel efficiency when using ethanol, including this one from Consumer Reports: The Ethanol Myth.

But today it came to my attention (via an essay by Geoffrey Styles) that a study recently published by Oak Ridge National Labs (ORNL) is the latest to show that you lose fuel efficiency on ethanol blends:

Effects of Intermediate Ethanol Blends on Legacy Vehicles and Small Non-Road Engines

E.4.1 Fuel Economy

• All 13 vehicles exhibited a loss in fuel economy commensurate with the energy density of the fuel.* With E20, the average reduction in fuel economy (i.e., the reduction in miles per gallon) was 7.7 percent compared to E0.

• Limited evaluations of fuel with as much as 30% ethanol were conducted, and the reduction in miles per gallon continued as a linear trend with increasing ethanol content.

Of course my friend will just respond that ORNL is clearly biased against ethanol and that the study is ridiculous. Either that or he will cherry-pick any favorable results, promote them, and ignore the unfavorable results.

So, while it is true that in theory one could make up some of the BTU deficit by going to engines with higher compression ratios – as I argued in All BTUs Are Not Created Equally – in the real world with real world engines the BTU penalty has to be paid.

Incidentally, the essay by Geoffrey Styles that I referenced earlier makes an interesting point. The ethanol industry is requesting an increase in the percentage of ethanol allowed for blending into gasoline from 10% to 15%. As Geoffrey points out, this is like a hidden tax on consumers, but the tax goes to the ethanol companies. The federal government actually loses out on the deal as well: “At the current average gasoline pump price of $1.93 per gallon, this would effectively raise the price by 3.4 cents per gallon, while reducing federal tax revenue by 2.2 cents.”

Given the power of the ethanol lobby in this country, we will probably end up doing it.

  1. By Clair on November 8, 2012 at 1:31 am

    Hi, I can’t find some of your sources, the links don’t work. Especially the source for the figures 10-13, it would be much appreciated if I could have this source in particular.

  2. By vs4 on March 7, 2013 at 11:50 pm

    I can tell you from my experience that my Toyota Matrix 2005 drops from 650 to 550 on 45 liters tank instantly if I fill up with 10% ethanol blend gasoline. So what is the point of 10% ethanol and 15% more fuel.

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