In a recent article in Energy Tribune, I pointed out that, based on my personal experience, using 10 percent ethanol in our motor fuel (E10) leads to an increase – not a reduction, in the demand for petroleum.

Those conclusions were based on fuel mileage measurements in my personal vehicle. Normally, this might be suspect since mileage is highly dependent on how the vehicle is used. E.g.: Local driving yields worse mileage than highway driving. For that reason, I corrected the observed tank fuel mileage for the average speed between fill ups. Not a perfect solution, but when miles per gallon was plotted against miles per hour for both pure gasoline (E0) and E10, the trend became clear. In the discussion to follow, I will show that not only does ethanol lead to increased oil imports, it also increases emissions of carbon dioxide – the gas that many people believe is causing global warming.

As I showed in the prior article, based on the thermal energy content of gasoline and of ethanol, E10 has about 3.32 percent less energy per gallon than 100 percent gasoline. It would not be unreasonable then to expect a miles per gallon drop of 3.32 percent with E10 vs. with E0. Any particular trip in a given vehicle takes a specific amount of energy, so if one fuel has less energy per gallon than another type of fuel, expect to require more gallons of the former. Thus, in theory, E10 should get 3.32 percent worse fuel mileage than pure gasoline.

Fuel Mileage vs. Average Speed Effect of Ethanol on 2008 Nissan Rogue

What does this tell us about carbon dioxide (CO2) emissions? Recall that to make a comparison of energy consumption, I hypothesized a trip that would require 100 gallons of pure gasoline. Burning one gallon of gasoline results in 19.56 pounds of CO2 being released to the atmosphere. Thus the trip would cause 1,956 pounds of this gas to be emitted. A gallon of ethanol, when burned, produces only 12.57 pounds of CO2. Gee, that’s great; clearly ethanol is the way to save the earth. Well, not so fast. Let’s examine how much CO2 is generated by our hypothetical trip, now made with E10. If, and it’s a big if, the mileage penalty for using E10 is 3.32 percent, there will be a saving of 7.3 pounds of CO2. That sounds pretty good, until you realize that a 100 gallon trip is 2,000 miles at 20 mpg. Then it doesn’t seem like much.

From my experience, and that of many others, the mileage loss with E10 is well over 3.32 percent. I have measured a mileage decrease of 7.8 percent. Let’s see what that does to the carbon dioxide emission comparison. The trip with E10 would require 107.8 gallons of E10, of which 97.02 gallons are gasoline and 10.78 gallons are ethanol. The gasoline would emit 1,898 lbs. of CO2 (19.56 x 97.02), and the ethanol would produce 136 lbs. (12.57 x 10.78). With E10, the total emissions of carbon dioxide would be 2034 pounds (1898 + 136). The calculation shows that if my vehicle is used for the trip that would take 100 gallons of pure gasoline, then burning fuel with 10 percent ethanol will create 78 pounds more CO2 than if the trip were made with unadulterated gasoline. (2034 - 1956 = 78).

Now this is a rather startling observation. If adding ethanol to our fuel does not contribute to energy independence, and it actually increases the emissions of what has become known as a greenhouse gas, then what on earth is the purpose of forcing American motorists to subsidize the producers and add this contaminant to our fuel?

You should be asking your representatives in the government about this.

Harry Wertheimer is a retired automotive engineer who lives in Salem, South Carolina.