If a gas station states their gas has up to 10% Ethenol, anyone know what's the maximum Ethenol that could be in their 93 Octane fuel? My understanding is that Ethenol decreases the Octane, so can they put very much in their "Hi Octane" fuel?
Ethanol will increase octane. I would expect the higher octane fuels to be very similar in percentage. Most of the blended fuels are pushing 10% (from what I was told).
The percentage of ethanol can vary depending on the base stock. But as others have noted, ethanol is an "octane booster." In theory, it should never be more than 10% of the soup we know as gasoline.
Ethanol is 100+ octane. it also carries less BTU's which means you need more of it to produce the same power. To tune for ethanol you need larger injectors or a program that lets more fuel thru the injectors on every fire. 10% seems to be a magic number because 10% also seems to be the amount of fuel trim a fuel injection car can compensate for w/o drivability issues, emission spikes CEL's etc. There are lots of threads out there where owners added a few extra gallons of e-85 into a non-ethanol vehicle and noticed reduced power and harder starting, as the mixture went past 25%.
87 octane containing 10% ethanol is still 87 octane...
Originally Posted By: QuOk
**87 octane containing 10% ethanol is still 87 octane...**
Yep,they just mix it with lower octane (cheaper) gasoline to get the same 87 octane.
LOL! Automotive grade pump gasoline, straight off the refinery (before addition of additives, etc.) their octane is typically in the late 60s/early 70s, and are the same batch of gas that will ended up in your pumping stations with various different degrees of additives to result in different octanes (it's the additives, get it?)
So bottomline: just because it's "doped" with less additives to provide knock resistance and yet to meet NA's automotive minimum octane standards doesn't necessary imply that these are "cheaper" gasoline to begin with.
Heh, knock resistance is what my Buick needs, and if E10 has less knock-resisting additives, that means the car knocks more, which means pulled timing, which means more fuel injected to make the same power, which means worse fuel economy.
Pure ethanol has higher octane than even straight premium gasoline by itself.
When mixed, it increases octane.
But who cares?
The final result is whatever the final result is!
93 octane is 93, no matter what means there are to get there. Whether it is additives or ethanol, or commonly a mix, we get what the pump says.
Since ethanol has less BTU energy than Gasoline, we suffer power/gas mileage loss when it is added to fuel, even though it is oxygenated.