it will burn just as fast as lower octane gas, but still harder to ignite, correct?
i got out of it, that higher octane fuels will withstand higher compression ratios and heat without self igniting.
so in a sense yes, higher octane fuels are harder to ignite.
an 87 octane, at say 185 compression on our bikes may "self ignite" (detonation) where a 93 octane will resist that pre ignition longer and ignite at the correct point of the compression/power stroke.
key points qouted from the article:
The octane rating of the fuel is directly related to its resistance to detonation. The higher the octane the higher pressures/heat the fuel can withstand before ignition. The rate at which this fuel burns has VERY little to do with the octane rating. The chemical soup of the fuel will determine the fuel's burn rate under IDEAL conditions. Since we KNOW that under combustion (active radicals, residual un-burnt mixes , squish action etc.) is NOT IDEAL, then this burn rate can not be properly established nor calculated. We do not need to know this burn rate because we will adjust our ignition and combustion chamber design to accommodate ANY burn rate. So, it is really irrelevant for us.
Does the higher octane fuel burn at a slower rate than lower octane fuel? IMO.. MAYBE, SOMETIMES, YES, and NO.. See above.. the rate of burn is dependant on many variables but to state that just because the octane is higher, then the burn is slower, is 100% incorrect.
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.
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.
To give you a good example of this, we contacted Jim Wurth from Sunoco Race Fuels. He explains, "
A perfect example is Sunoco Maximal, which is our fastest burning fuel, and coincidentally one of Sunoco's highest octane fuels at 116 (R+M) / 2. A lot of Pro Stock teams rely on Maximal for those sub-seven second runs. When they are turning 9,000 rpm or more, the fuel has to burn pretty quickly to achieve complete combustion".
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