E85 is 85% ethanol, 15% gas (and e15 is the other way around)
Octane rating is a measure of how much you can compress a fuel before it ignites by itself. Higher octane gas is more resistant to that. (And e85 actually has a pretty high octane rating, usually somewhere north of 100. Regular gas often contains up to 10% ethanol, in part because it boosts the octane rating)
To expand on that a bit, if you compress gas enough, at a certain point it just catches fire on its own. This is actually a big part of how diesel engines work. Diesel is actually pretty hard to ignite, in some cases you can even put out small fires by pouring diesel on it (don’t try this at home) so they rely on getting high enough compression in order to work.
Gasoline is a lot more flammable though, you don’t really need to compress it at all for it to burn. Sure, ideally you probably want a certain compression ratio because something something stoichiometry but gas is more forgiving in that regard. As long as your air-fuel mixture is about right, it’s gonna burn when your spark plug goes off.
In fact, gas is maybe a little too forgiving, if your octane rating is too low and your engine compression is too high (mostly a problem with higher-performance engines) that gas can just kind of go off too early before the spark plug goes off, which causes “engine knock” which will cause damage.
But the other way around, high octane in a lower compression engine, basically does nothing spectacular. It still goes boom when the spark plug goes off and not until then.
I think you’re confusing e85 with 85 octane gas
E85 is 85% ethanol, 15% gas (and e15 is the other way around)
Octane rating is a measure of how much you can compress a fuel before it ignites by itself. Higher octane gas is more resistant to that. (And e85 actually has a pretty high octane rating, usually somewhere north of 100. Regular gas often contains up to 10% ethanol, in part because it boosts the octane rating)
To expand on that a bit, if you compress gas enough, at a certain point it just catches fire on its own. This is actually a big part of how diesel engines work. Diesel is actually pretty hard to ignite, in some cases you can even put out small fires by pouring diesel on it (don’t try this at home) so they rely on getting high enough compression in order to work.
Gasoline is a lot more flammable though, you don’t really need to compress it at all for it to burn. Sure, ideally you probably want a certain compression ratio because something something stoichiometry but gas is more forgiving in that regard. As long as your air-fuel mixture is about right, it’s gonna burn when your spark plug goes off.
In fact, gas is maybe a little too forgiving, if your octane rating is too low and your engine compression is too high (mostly a problem with higher-performance engines) that gas can just kind of go off too early before the spark plug goes off, which causes “engine knock” which will cause damage.
But the other way around, high octane in a lower compression engine, basically does nothing spectacular. It still goes boom when the spark plug goes off and not until then.