Bioethanol water mix (e.g. overproof Rum or vodka e.g. Stroh 80) as an engine fuel?

It might well be safer to use synthetic denatured ethanol rather then E85. It is perfectly easy to use a glo plug with an ethanol fuel. Whoever started the nonsense about ethanol not reacting right with the catalyst on the glo plug is nuts. It will react just fine. So will lots of other organics. A few years ago someone talked about making fuel from laquer thinner. His engines ran just fine. Laquer thinner is a mix of mainly acetone and MEK generally. Maybe a bit of toluene to slow evaporation. Such a fuel will give you a bit less power then ethanol.

But the glo plug does present some problems. It is pretty easy to poison the precious metal catalyst coating. E85 manufacturers are going to put a variety of detergents in the fuel to help keep the engine clean. They have been doing this with regular gasoline forever. I suppose it will also have a dye in it so no one mistakes it for water. These detergents and dyes could well cause glo plug life problems. They would not cause any problem at all in a spark ignition engine as such engines do not depend on any catalytic activity. In fact they are designed to avoid catalytic things happening. But in a glo engine the catalytic activity is what keeps the engine running.

The other advantage of synthetic ethanol is it is not loaded with all the fusel oils that might be in E85. Industrial fermentations are not run at low temps like fermentations meant to produce booze, beer or wine. As the fermentation temp goes up the amounts of fusel oils produced also goes up fast. I doubt if the distillation process to isolate the ethanol from the fermentation mix is all that great at cutting out the fusel oils. I doubt it if for no other reason then if it did cut them out they are a waste stream the corn fermentation guys would have to pay to have disposed. So it is in their interest to leave them in the ethanol as much as possible. These things would not cause any problem in a spark ignition engine but might well cause fouling in a glo engine. If they foul the glo plug you have a dead engine. If you really have your heart set on being green at least use solvent grade bioethanol rather then fuel grade. Solvent grade is going to have fewer byproducts in it.

Synthetic ethanol on the other hand is made from chemical processes that do not use fermentation at all. So fusel oils are not a problem. And synthetic ethanol will only have the denaturant in it which is usually methanol anyhow. Not a bunch of other added stuff that may vary from brand to brand. The current price of synthetic ethanol is about $3 a gallon. You would need to buy at least a 55 gallon drum to get this kind of price, plus of course add the price of the drum itself.

You are not going to get as much power out of an engine running on ethanol as on methanol. The amount of oil added to the fuel will make essentually zero difference in how much power you get out as long as it is adequate to provide the needed lubrication. The reason it will not impact power out is it goes thru the engine unburned and unvaporized so is simply along for the ride. The amount of power is wholly dependant on things like BTUs burned per cycle and the difference between peak gas temp in the combustion chamber and exhaust gas temps. With ethanol you simply can not get as many BTUs per cycle as you can with methanol. The reason is ethanol takes more air per BTU of heat produced then methanol requires. All that extra air decreases power output by limiting the amount of ethanol you can stuff in the combustion chamber per cycle. But it is not a big penalty. If methanol will run an engine at one horsepower then ethanol will probably give you 0.85 horsepower. You could compenstate by going down a bit on prop size and still run at an efficient rpm.