Gas station pump offering five different octane ratings.The octane rating is a measure of resistance to gasoline and other fuels to blow up (engine knocking) in spark ignition internal combustion engines. High-performance engines typically have higher compression ratios and are therefore more likely to blow up, so they require higher octane fuel. A decline in performance does not drive better performance in general with the high-octane fuel, where the compression ratio is fixed through the design of the engine.
Measured by the number of octane fuel in the engine test, known by comparison with a mixture of heptane iso-octane and normal, which will have the same ability of anti-hit as fuel under test: the percentage, by volume, of the ISO - octane in the mix is the octane rating of fuel. For example, the gasoline with the same knocking characteristics as a mixture of 90% ISO-octane and heptane have 10% of 90 octane. because some fuels are more resistant to a variety of ISO - octane, has been expanded to allow the definition of the octane numbers higher than 100.
Definition of octane
The octane rating of the engine spark and fuel resistance is the bomb (an anti-knock rating) compared with a mixture of ISO - octane (2,2,4 - trimethylpentane, an isomer of octane) and n heptane. By definition, is set to ISO-octane octane rating of 100 and heptane is assigned to the octane rating of zero. And 87 octane gasoline, for example, have the same anti-knock rating of a mixture of 87% (by volume) ISO - octane and 13% (by volume) n heptane. This does not mean, however, that the gasoline actually contains these hydrocarbons in these proportions. It simply means that it may blow up the resistance and the same mixture described.
Octane is not related to the energy content of fuel (see heating value). It is only a measure of the tendency of fuel to burn rather than explode.
Measurement methods
The most common type of octane in all parts of the world and the Research Octane Number (RON). RON is determined by running the fuel in the engine test with a compression ratio under changing conditions of control, and compared the results with those of a mixture of ISO - octane and n heptane.
There is another type of octane rating, called Motor Octane Number (two) or lean rating octane aviation, a better measure of how the fuel behaves when under load. Two test engine uses a test similar to those used in testing the RON, but with a preheated fuel mixture, a top speed of the engine, and variable ignition timing to keep the pressure on the fuel knock resistance. Depending on the configuration of the fuel, the two modern gasoline that about 8 to 10 points lower than RON. Usually require a fuel specifications, both RON minimum and two as a minimum.
In most countries (including all of Europe and Australia) in the classification of "title" octane, as shown on the pump, is Ron, but in the United States, Canada and some other countries in the number of title is the average and two of RON, and sometimes called the index antiknock (AKI), Road Octane Number (RdON), Pump Octane Number (PON), or (R + M) / 2. 8-10 point difference as referred to above, and octane display in the United States is 4 to 5 points less than the same fuel elsewhere: 87 octane fuel, and "regular" gasoline in the United States, Canada, 91-92 in Europe. But most European countries provide pumps 95 (RON) as "regular", equivalent to 90-91 U.S. (R + M) / 2, and some even 98 (RON) or 100 (RON)
It is possible to have the fuel's RON greater than 100, because iso-octane content is most striking resistance available. Can fuel and racing, and AvGas, liquefied gas and alcohol fuels such as methanol or ethanol and octane ratings of 110 or higher - RON Ethanol is a 129 (two 102, AKI 116). "Octane booster" model include the gasoline additive tetraethyl lead, MTBE and toluene. Decompose easily tetraethyl lead (the additive used in leaded gasoline) to the roots of its constituent, which reacts with the radicals of the fuel and oxygen, which begins in the combustion, thereby delaying ignition, leading to increase octane number.
♦ hydrogen does not fit well in the definitions of normal octane number. RON has a very high and low two , so that it has low resistance to knock in practice , due to the low ignition energy (mainly due to the low dissociation energy) and very high speed flame. These qualities are very desirable in rocket engines, but is undesirable in Otto cycle engines. However, mixing the secondary component (eg, in bi-fuel vehicle), and hydrogen raises the knock resistance overall. Flame speed is limited by the rest of the component species; hydrogen may reduce knock by contributing to the high thermal conductivity.
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