Finally, a definite answer: Do not use fuel containing ethanol in two-cycle engines

I recently received a note from a gentleman who read my column on how to dispose of fuel that was a mixture of 100LL and auto fuel containing ethanol (What if my plane is filled with the wrong fuel? Nov. 3 issue). His suggestion was to “”just use it in your leaf blower or any other two-cycle-powered yard equipment.”"


I recently received a note from a gentleman who read my column on how to dispose of fuel that was a mixture of 100LL and auto fuel containing ethanol (What if my plane is filled with the wrong fuel? Nov. 3 issue). His suggestion was to “”just use it in your leaf blower or any other two-cycle-powered yard equipment.”"

Now the great part of this is that I can finally give someone a definite answer: No, absolutely not.

There are two major effects from using fuel that contains ethanol. The first is water solubility. Ethanol is a polar solvent so it absorbs water. This is a big concern for airplanes because when the ethanol absorbs water from the bottom of a tank, it also picks up all of the dirt that was in the water. This leads to problems in the fuel system and can result in a pilot getting some dead stick landing practice, which may not be at a clear landing location.

The other major concern with ethanol is that it contains oxygen. This means that the stoichiometric air fuel ratio (the ideal for complete fuel burn) will be lower than for a straight hydrocarbon fuel. Therefore, a fuel containing ethanol will effectively lean out the air fuel mixture. Most modern auto engines have oxygen sensors, which can richen the mixture when an ethanol blend fuel is used. Additionally, almost all auto engines are water cooled and operate at fairly low power settings most of the time.

In most two-stroke engines, the metering is fixed, so when an ethanol blend is used, the engine will run leaner unless the carburetor is re-jetted. Almost all carbureted two-stroke engines are jetted to run on the rich side of stiochiometric. This is needed for power and proper engine cooling. Therefore, if you use an ethanol-blended fuel, it can lean out the mixture, which in turn will raise the temperatures in the cylinders, which can lead to a scuffed piston and possible engine failure.

My primary concern is not for the mechanical well being of your leaf blower, but for the many ultralight aircraft that use two-cycle engines. Almost all of them are designed to run on auto fuels and most of the time they are operated at or near full power. Since they are usually air-cooled, they tend to run near the maximum allowable piston temperatures.

If an ethanol-containing fuel is used in one of these applications, it would be necessary to re-jet or adjust the carburetor for the lower energy containing fuel. Failure to do so could lead you back to the dead stick landing exercise ? and we all know how some of those turn out.

It is also important to remember that in many areas of the country all auto fuels contain ethanol ? and the fuels may not be labeled as ethanol-containing fuel. If this doesn?t worry you enough, there is a bill in Congress that would require all auto fuels to be blended with at least 10% ethanol in a few years.

Ben Visser is an aviation fuels and lubricants expert who spent 33 years with Shell Oil. He has been a private pilot since 1985. You can contact him at Visser@GeneralAviationNews.com.

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