100 Octane Fuel? Thinking about using!
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Joined: Jun 2004
Posts: 92
Likes: 0
From: Portland OR
Keep telling yourself that. Higher octane does help in preventing detonation. It does NOT mean you can just add timing. What a simplistic and wrong way to summarize octane ratings, you should really pick up a book or do some research before ou try and offer advice in a tech section again.I DID NOT SAY "MEAN" you can I said "HELP" you add timing...
Burning Brakes
Joined: Aug 2006
Posts: 789
Likes: 38
From: Shreveport LA
Maybe YOU should read what your OWN state has to say about Octane and burning.... See Link Below D.S.http://dnr.louisiana.gov/sec/execdiv.../trans/b/b.htm
I will quote it for you...."Posted octane numbers on gasoline pumps are a result of testing fuel performance under laboratory and actual operating conditions. The higher the octane rating on fuel the less volatile (evaporative qualities) and the slower the fuel burns
Of Course this IS an simplification......I will Explain Why it is Still TRUE!
Octane is a measurement of a fuel's resistance to ignition. Ideally, the air/fuel mixture will ignite at the proper time and burn smoothly through the power stroke. The idea is that one powerful combustion of the air/fuel mixture is better than several randomly-ignited small flame fronts. When you can precisely control the point at which the fuel will ignite, maximum performance of the engine can be achieved, and power-robbing knock and ping will be eliminated. Knock and ping are a result of abnormal ignition, or multiple flame fronts colliding within the combustion chamber during the compression stroke.
Octane is a measurement of a fuel's resistance to ignition. Ideally, the air/fuel mixture will ignite at the proper time and burn smoothly through the power stroke. The idea is that one powerful combustion of the air/fuel mixture is better than several randomly-ignited small flame fronts. When you can precisely control the point at which the fuel will ignite, maximum performance of the engine can be achieved, and power-robbing knock and ping will be eliminated. Knock and ping are a result of abnormal ignition, or multiple flame fronts colliding within the combustion chamber during the compression stroke.
All reputable fuel manufacturers determine the octane rating of their gasoline in the research lab using a special, dedicated single cylinder engine. Comparing the gasoline to a series of standard reference fuels in the test engine results in either a research octane number (RON) or a motor octane number (MON) depending on a set of operating conditions. The RON is determined with the test engine operating at 600 rpm, at standard barometric pressure, and the intake air temperature set at 125 degrees Fahrenheit. RON is primarily used to address part-throttle knock and ping problems. The MON addresses wide open throttle operation and is determined with the test engine spinning at 900 rpm, also at standard barometric pressure, and the intake air temperature pumped up to 300 degrees.
The best predictor of a fuel's performance in a street/strip machine is the Anti-Knock index (AKI). This is simply the average of the RON and MON numbers, or (RON + MON) / 2. Most all octane ratings posted at the pumps are determined by this AKI formula, and are the minimum values you could expect to see.
The best predictor of a fuel's performance in a street/strip machine is the Anti-Knock index (AKI). This is simply the average of the RON and MON numbers, or (RON + MON) / 2. Most all octane ratings posted at the pumps are determined by this AKI formula, and are the minimum values you could expect to see.
The minimum octane requirement
of your engine is determined by several variables besides the compression ratio. The engine and cylinder head configuration, air/fuel mixture, timing, coolant temperature, atmospheric pressure, relative humidity, and ambient air temperature will also affect the octane required to make your mill produce maximum power.
of your engine is determined by several variables besides the compression ratio. The engine and cylinder head configuration, air/fuel mixture, timing, coolant temperature, atmospheric pressure, relative humidity, and ambient air temperature will also affect the octane required to make your mill produce maximum power.
The burn rate of a fuel is a measurement of the time required for complete combustion of the air/fuel mixture. The notion that octane ratings affect the burn rate of fuel is about 180-degrees from reality; burn rate is a function of several variables, and the two are completely independent, although there is generally a correlation between octane ratings and burn rates.
That last statement is geared towards people like you who seem to rationalize this rather than learning the real reasons higher octane prevents detonation.
Here is a FAQ that has more information than you could possibly understand but seems to be the most definitive resource for this discussion.
http://www.faqs.org/faqs/autos/gasoline-faq/
I have found that this FAQ has been distributed extensively by many universities and their petroleum engineering departments. I have been unable to find any posts that cite erroneous information in this FAQ. If you find this FAQ to be in error, many people will be very interested in your alternate sources, and you will do a lot of folks a great service.
First, under section 6.3, I offer you the following statement:
"The antiknock ability is related to the "autoignition temperature" of the hydrocarbons. Antiknock ability is _not_ substantially related to:-
1. The energy content of fuel, this should be obvious, as oxygenates have lower energy contents, but high octanes.
2. The flame speed of the conventionally ignited mixture, this should be evident from the similarities of the two reference hydrocarbons. Although flame speed does play a minor part, there are many other factors that are far more important. ( such as compression ratio, stoichiometry, combustion chamber shape, chemical structure of the fuel, presence of antiknock additives, number and position of spark plugs, turbulence etc.) Flame speed does not correlate with octane.
This is correlated by reviewing the basic characteristics of both heptane and octane. In section 4.9 we discover that the heat of combustion of heptane and octane are very nearly identical. Hence there is no physical process based on physical properties that could cause a different rate of burn.
Fuel State Heat of Combustion Research Motor
MJ/kg Octane Octane
n-heptane l 44.592 0 0
g 44.955
i-octane l 44.374 100 100
g 44.682
toluene l 40.554 124* (111) 112* (94)
g 40.967
2-methylbutene-2 44.720 176* (113) 141* (81)
Next, under section 4.11, the author states:
"Combustion Characteristics
As gasolines contain mainly hydrocarbons, the only significant variable between different grades is the octane rating of the fuel, as most other properties are similar. Octane is discussed in detail in Section 6. There are only slight differences in combustion temperatures ( most are around 2000C in isobaric adiabatic combustion [45]). Note that the actual temperature in the combustion chamber is also determined by other factors,
such as load and engine design. The addition of oxygenates changes the pre-flame reaction pathways, and also reduces the energy content of the fuel. The levels of oxygen in the fuel is regulated according to regional air quality standards."
Simply put, gasoline burns just about the same, no matter what is in it. As a final example, take a look at the characteristics of octane and heptane from section 6.1:
Fuel Melting Point Boiling Point Density Vaporisation
normal heptane -90.7 98.4 0.684 .365 @ 25C
iso octane -107.45 99.3 0.6919 .308 @ 25C
The numbers are nearly identical.
So, from a chemistry point of view, different rates of burn based upon octane are a myth. Then again you can THINK anything you would like.
Last edited by Blue02ws6; Jan 8, 2007 at 09:17 PM.
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I'd just run the 93 or so octane in the tank. You'll probably get just as good of performance out of the car.
