I know something about this from my experience with automotive engines.
The issue isn't so much the engine itself, which really doesn't care what fuel it burns as long as the fuel has a burn characteristic that is within the engines design parameters. (Compression ration, maximum cylinder pressure, timing, ignition system, etc.)
The issue arises from the fact that unless the entire fuel system was engineered for alcohol, it will tear it up. Older fiberglass tanks, non-synthetic hoses, gaskets/O-rings/sealants in carburetors and fuel injectors... all subject to being destroyed by alcohol.
I have been given to understand that in applications where your fuel sits in your tank for an extended period of time you could run into issues like phase separation and should therefore use fuel stablizers, but then again, you should be using fuel stabilizers in that situation anyway.
Typically, engines and fuel systems built in the last decade can be reasonably presumed to be able to tolerate up to 10% ethanol content, but personally, I would check the owner's manual first. If that wasn't available I would call the manufacturer.
One last thing...
Alcohol is very fond of water. In a high humidity environment it will suck it right out of the air. For this reason alone I personally like to use marine fuel in my boat, not automotive fuel. And that's coming from someone who actually LIKES alcohol fuel. (E85 can be a hot rodder's best friend.)
If God didn't want me to walk on the grass, he wouldn't have left it on the ground.