93 Octane??

Pretty good guess. It was from 1991.

Ed

 

No, this much more comprehensive one:

http://www.faqs.org/faqs/autos/gasoline-faq/part1/

DS

 

My 2004 mini-van from Chrysler comes with information in its owner's book
advising against the use of high octane fuel.

Dan correctly noted that there are many ways to increase octane and some of
those ways introduce additives and cylinder conditions that are not within
the design limits of a motor not designed for to run on such fuel.

Richard.

 

Whoops, those are not my words, nor an accurate paraphrase of them.

DS

 

I intended my attribution to your statement to be limited to the following:
(Sorry if that was not clear). My additional statement is based upon my
experience one year at Mobil's Research Lab and as the individual who helped
establish the NYS Fuel Quality Assurance Program.

Richard.

"There are a great many refining techniques and chemicals that are used
to increase the octane rating of unleaded fuel. The addition of MTBE and
"alcohol" (ethanol) are only two of them."

DS

 

Yep, that works. Thanks.

DS

 

Steve,
Does higher octane fuel burn slower (slower moving flame front) - less
like an explosion than lower octane?

Bill Putney
(to reply by e-mail, replace the last letter of the alphabet in my
address with "x")

 

In addition, the volatility of the fuel is altered depending on season to ensure
less volatility in the summer, and acceptable performance in the winter. Of
course this assumes you are in a place with real seasons.

 

It's mainly harmful to the wallet. Gasoline with higher antiknock index
numbers ('octane') can give you lower mileage if your engine isn't designed to
take advantage of it, since the antiknock index increasers can contain less
energy per unit than gasoline, which they displace.

 

I don't think this is correct. RVP is the measure of volatility and
octane is an indirect measure of the speed of the combustion wavefront.
Not the same thing at all.

In the northeast our volatility changes dramatically from winter gas to
summer gas, yet the octane ratings remain the same.

I agree with your last statement here. I know of no harm from using
higher octane fuel other than to your wallet. Maybe there is harm, I've
just never seen it documented or supported by data.


Matt

 

Did it say why?


Matt

 

Do you have a reference for this? Hadn't heard this before, but I'm not
saying it isn't true. However, I would like to see a reference to read
about this.


Matt

 

http://www.chevron.com/prodserv/fuels/bulletin/oxy-fuel/enrgycon.shtml

The difference between gasoline and gasoline containing 10% ethanol is not huge, but
it is not insignificant either, at 3.4%.
Unfortunately the chart only lists MTBE and ethanol, which may be used for air
pollution control (oxygenate properties) as well as increasing AKI. In addition,
higher octane fuel requires more energy to produce at the refinery.

 

Probably not, because its at best a "CYA" on the part of the
manufacturer. Covering themselves "just in case" some high-octane fuel
is found that still contains lead or manganese (kills the O2 sensors and
the cat),or various non-lead additives that aggravate combustion chamber
deposits, valve stem and intake port deposits, etc. With a good-quality
(major name brand) modern unleaded, the only thing that's going to be
harmed by running a fuel with a "too high" octane rating is your wallet.

 

MTBE is certainly an effective octane-booster. I don't know about under
the current EPA gasoline rules, but for a number of years around my
area, only 93-octane fuels contained MTBE at all, and it was there
strictly to hit the 93 octane rating. The lower graded fuels were MTBE-free.

 

Bill Putney wrote:

I'm not sure on that one, but I'd wager that if it does its an
incidental side-effect of the additives that resist self-ignition. The
ideal Otto cycle calls for a rapid (near explosion but still a
controlled 'burn') iso-volume delivery of heat energy at TDC, just like
the ideal Diesel cycle calls for a constant iso-pressure delivery of
heat energy all the way from TDC to BDC. Both cycles run somewhere
between the two in the real world, but deliberately slowing the flame
front in an Otto cycle engine (especially a high-compression and
therefore high-performance engine) is probably not desirable.

I know just enough about combustion dynamics to be dangerous (pun
intended) but my understanding is that a chemical's resistance to
self-ignition can be changed without altering its burn rate or burn
characteristics significantly or at all. In theory. In the real world,
almost all parameters get "coupled" because you're changing fractional
content of different chemicals every time you change a parameter. That's
why the oil companies still need so many Ph.D chemists, after all these
years. If they really did nothing but bribe governments, rape the
environment, suppress competitive innovation, and ream the consumer the
way some people believe, they certainly wouldn't need chemists

And a lot of characteristics of fuels are very counter-intuitive. People
think of gasoline as being more energetic than, say, motor oil or diesel
because its so much more prone to combustion. But diesel, motor oil, and
most oils have more energy per gallon than gasoline. Or to go to an
extreme, think about diesel versus explosives. Diesel, gasoline, and
candle wax all contain much more energy per pound than even high-powered
high-tech explosives, but the WAY they burn (burn rather than a true
supersonic detonation wave) makes them seem less energetic.

 

Just testing octane is expensive. With the changing formulations needed to
meet performance, emissions and cost criteria it would be cost prohibitive
to run the tests needed to confirm. But remember, higher octane fuel has
other consequences other than retail cost, it takes more base gasoline to
formulate so it wastes natural resources as well.

Richard.

 

I've never had a vehicle deliver poorer mileage on premium than on
regular. I have had several that gave enough increase in mileage to
more than cover the price spread. The price spread was a little lower
back then than it is today in pennies per liter, but in percentage it
was likely pretty close.

 

Not exactly true. Octane is a measure of the anti knock index. The
fact that the volatility, or vapour pressure is SOMETIMES higher on
hightest is only an artifact, not a cause.
Adding propane (octane of 150 more or less) to gasoline will raise
both octane and volatility. Adding TEL changes the octane, without
affecting volatility.

The octane of gasoline can be modified in production by changing the
ratio of hydrocarbon "fractions" in the distilation process. The old
hightest white gas was lead free and had high octane, but was VERY
expensive to produce at the time - hense the introduction of TEL.

 

Comparing mileage with different fuels is very difficult, because you have no
control group for the experiment. Every auto trip is different, even along the
same route you may encounter different conditions, traffic or get more red lights,
etc. The difference in mileage due to gasoline can easily be less of a factor than
such outside factors.