How does adding ethanol effect the octane rating of gasoline?

Question

Would it be helpful to put a gallon of ethanol in my tank each time I fill up?

Answer 1

Ethanol increases the octane rating of gasoline.  E85 which is 85% ethanol and 15% gasoline has an octane rating of 105.  Adding a gallon of ethanol when you fill up is good for your car's engine and fuel system.  It removes water as well as deposits and it helps your engine burn fuel at a cooler temperature.  It also burns cleaner than gasoline, preventing future engine deposit build-up.  Keep adding that ethanol!

Answer 2

It increases it.  But, you need to use fuel grade ethanol with a minimum concentration of 95%.  Lower concentrations may not mix with gasoline.  Ethanol has a blending octane value of 113.

Answer 3

I wouldn't mix it in my gasoline unless my car was designed to take ethanol.  And if it was designed for that, I would only buy the E85 from gas stations.  Why mess with something you don't know anything about?

Answer 4

I think alcohol burns slower.  It's less volatile.  It also produces less energy per gallon.  That's why it's a less efficient fuel.  The problem is I don't know how much affect it would have just mixed with the gasoline.

It's also supposed to be an oxygenate, which implies it helps the gasoline burn; so that part sounds like it would lower octane.  I guess you need a real chemist who works in the petrochemical industry.

Higher octane rated fuel burns slower and so it builds pressure slower.  That's why it's less inclined to knock.  It also might be less efficient on short stroke engines but more efficient on longer stroke engines for that reason, depending on rpm operating ranges.

The differences in today's octane ratings, though, are only a few points so there probably wouldn't be a noticeable difference.

I think the old high compression fueled drag racing engines used alcohol and nitromethane for knock  resistant qualities.  I assume the nitromethane was to boost the energy output of the fuel.

Don't try running that in your car.  They need to be set up for it.  You can't run long on it and probably need special engine components that can tolerate it even for a short run.

Answer 5

ethanol raises the octane rating of gasoline. how much depends on how much ethanol you add. ethanol does this because it burns colder than gasoline does, and thus reduces the temperature in the combustion chamber.

and george, nitromethane detonates fairly easily when combustion temperatures rise, but it doesnt light off easily, which is why methanol is added to the fuel mixture, 98% nitromethane to 2%methanol in top fuel engines. by half track though the spark plugs electrode have melted away and the engine is running on controlled detonation, much like a diesel engine does.