Then it must have an engine that is designed for multi-fuels and can adjust itself. Known as Flex-fuel I believe.
Alcohol is about 30% less explosive than gasoline, that means 30% less energy. If you run E-85 in a standard fuel engine, you will get less MPG.

Some things that most people don't know about Octane and Gasoline. Try and think of it like the old days of black powder and smokeless gun gunpowder. With black powder you could take a little pile of it, light it with a fuse, big poof like old time flash powder for cameras, highly explosive, less energy. This is like low octane gas, lower octane gas actually explodes easier, faster, under less pressure, so it stores up less energy before it goes kaboom in your engines cylinders making your motor run.

Make a little pile of smokeless powder, it burns slower, it stores up more energy before it goes kaboom, same for higher octane gasoline, it takes more pressure, can be loaded more before it goes kaboom in your engine.

Higher octane or lower octane gas will not really affect your gas mileage. The reason for them is how your engine is designed to take advantage of the octane rating of gasolines, and for some engines the octane is critical. Most higher performance engines need to have higher octane gasoline because they run at higher compression ratios. The muscle cars of old ran some very high compression ratios, some 12 to 1 or higher.

This loaded a lot of energy in that cylinder before the gas exploded, thus giving higher horse power. The octane ratings were high decades ago, so they could do that. If you run too low an octane in an engine that is designed for say 93 octane minimum, what happens is that the fuel air charge explodes before the spark plug actually lights it off just from the high cylinder pressure. This is called pre-ignition, sometimes called "knocking" maybe you remember a car or two that "dieseled" on you once or twice, ran after you turned the engine off, this from the fuel self exploding with no spark required. Pre-ignition is very damaging to your engine, it will destroy internal parts, major parts such as connecting rod bearings.

If your engine is designed for high octane gas, you must run that minimum octane rated gas or risk doing serious damage. If your engine is not designed for it, it gives little to no benefit at all to run fuel with a higher octane than the minimum required because your engine is not designed to take advantage of it.

If I'm not mistaken Toluene is what the gas companies use to boost octane ratings, I know that's what the old muscle car heads use if they need more octane. Those Discount auto octane boosters like "Firepower 104" pretty much do squat. I believe it's somewhere around 1 gallon of Toluene to 15 gallons of gas to raise the octane about 5 or 6 points, makes the difference if you have a high compression/performance engine and there is no high octane gas available.