Quote:
Originally posted by MrSelfDestruct
That was a very interesting read. I have three questions that I've been wondering about.
How do fuel companies produce gas with different octane ratings, and does it cost anywhere near the extra thiry cents per gallon that we pay, to propduce?
|
All gasoline starts off @ 70 octane and it depends on what the terminal uses to boost octane. There are several different options, but none of them are very expensive. FTC recommendations say that if your car's manual says to use "regular" (87 octane) then use that gasoline. No benefit of horsepower will be gained by using high octane fuel -- its wasted on smaller engines. None whatsoever. Its not even cleaner. If your engine knocks or pings, then definitely upgrade to a higher octane fuel because _long term_ knocking will destroy your engine. But, unless you're driving a Porsche with twin turbo, you probably won't have ANY problems with 87 or 89 octane fuel. To answer your question though, since all gasoline is distilled at 70 octane, and all fuels must have additives to boost octane, then no -- its not that much more expensive to boost octanes to 91 or 93 beyond the 87 required by law. The question is, do you NEED the 91 or 93. Probably not...
Quote:
So if the octane rating is the way gasoline behaves as opposed to a mixture of octane and heptane, does 113 octane fuel take 13% more pressure to detonate than pure octane?
|
I believe that most 113 gasoline uses ethanol to increase its rating. Since the octane scale is a relative one, then greater than 100 ratings exceed pure octane's pressurization point -- meaning, you can pressurize the fuel/air mixture further than pure octane before it detonates without a spark. This is important in high compression engines like airplanes and nascar. Remember, the octane rating system is only a _comparison_ of gasoline to pure isooctane ... (BTW, a 9:1 ratio of gasoline to pure ethanol will yield 3 additional octane points)
Quote:
Also, how approximate are the ratings at the pump? I assume that it's impossible to make a perfectly uniform mixture, but how close is it?
|
Fairly close. There is a process by which, a single cylinder engine is run using the gasoline in a lab. There are 2 averaged measurements that go into the tabulation of the total octane rating of a gasoline. These are in turn, averaged together. The sample pools are large enough to account for some margin of statistical error. Basically, the numbers are close enough to their integer labels. The only errors occur in the decimal places...