octane number

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Related to octane rating: compression ratio, Cetane rating, Engine knocking

octane number,

figure of merit representing the resistance of gasolinegasoline
or petrol,
light, volatile mixture of hydrocarbons for use in the internal-combustion engine and as an organic solvent, obtained primarily by fractional distillation and "cracking" of petroleum, but also obtained from natural gas, by destructive distillation
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 to premature detonation when exposed to heat and pressure in the combustion chamber of an internal-combustion engine. Such detonation is wasteful of the energy in the fuel and potentially damaging to the engine; premature detonation is indicated by knocking or pinging noises that occur as the engine operates. If an engine running on a particular gasoline makes such noises, they can be lessened or eliminated by using a gasoline with a higher octane number. The octane number of a sample of fuel is determined by burning the gasoline in an engine under controlled conditions, e.g., of spark timing, compression, engine speed, and load, until a standard level of knock occurs. The engine is next operated on a fuel blended from a form of isooctane that is very resistant to knocking and a form of heptane that knocks very easily. When a blend is found that duplicates the knocking intensity of the sample under test, the percentage of isooctane by volume in the blended sample is taken as the octane number of the fuel. Octane numbers higher than 100 are found by measuring the amount of tetraethyl lead that must be added to pure isooctane to duplicate the knocking of a sample fuel. At present three systems of octane rating are used in the United States. Two of these, the research octane and motor octane numbers, are determined by burning the gasoline in an engine under different, but specified, conditions. Usually the motor octane number is lower than the research octane. The third octane rating, which federal regulations require on commercial gasoline pumps, is an average of research octane and motor octane. Under this system a regular grade gasoline has an octane number of about 87 and a premium grade of about 93. Most American-made cars that were built in the 1971 model year or later can use regular gasoline. To prevent knocking, premium grade gasoline must be used in many cars built before 1971 and in some new cars that have high-performance engines.

Octane Number


an arbitrary quantitative characterization of the antiknock qualities of motor fuels used in carburetor internal-combustion engines. The octane number is determined by comparing the fuel being tested with secondary standard fuels. The primary standards are isooctane, whose high antiknock value is arbitrarily assumed to be 100 on the octane scale, and n-heptane, whose antiknock value is assumed to be zero. The antiknock value of the fuel being tested is characterized by determining the composition of the mixture of isooctane and n-heptane that has an equivalent antiknock value. Quantitatively, the octane number indicates the percentage of isooctane (by volume) in the reference mixture.

The octane number is determined under standardized conditions using special, small one-cylinder engines according to one of three methods (the motor method, the research method, or the temperature method), which differ in the operational parameters of the engine. The motor method is used for evaluating aviation gasolines and automotive gasolines with octane numbers 65–100; the research method, for automotive gasolines; and the temperature method, in testing high-octane aviation gasolines and their high-octane components with octane numbers 90–115, and also in determining the quality grade of gasolines. The octane number characterizes the fuel under conditions of a lean mixture (excess air ratio, 0.9–1.1).

octane number

[′äk‚tān ‚nəm·bər]
A rating that indicates the tendency to knock when a fuel is used in a standard internal combustion engine under standard conditions; n-heptane is 0, isooctane is 100; different test methods yield other values variously known as research octane, motor octane, and road octane.

octane number

, rating
a measure of the quality of a petrol expressed as the percentage of isooctane in a mixture of isooctane and n-heptane that gives a fuel with the same antiknock qualities as the given petrol
References in periodicals archive ?
In contrast to prior efforts, this work examines new octane impact metrics that seek to represent the impact of octane rating on certification drive cycles and as a function of powertrain output power.
The need for more fuel with a higher anti-knock index is boosting demand for blending components with higher octane ratings ("Engine design trends lead to increased demand for higher-octane gasoline", EIA, Apr 2016).
Pyrolysis oil can also be added to gasoline to increase its octane rating. The remaining butane and methane are recycled and reused to fuel the process.
The volatile Jeffrey-pine pitch was later analyzed and found to contain a form of heptane so pure that it was eventually used to define the zero end of the octane rating system for gasoline.
Gasoline with an octane rating of 95 is now sold at P54.05 to P64.27 a liter.
Compared with the euro 399.40/1,000 litres recorded on April 18, average pre-tax prices of unleaded Euro-super (95 octane rating) in the EU-25 fell back to euro 396.47/1,000 litres on May 9.
A liter of gasoline with an octane rating of 95 is now in the range of P51.00 to P62.83 while a liter of kerosene is now at P47.67 to P57.85.
By launching the unit octane rating of the refinery has raised from 64 to 88, the official said, adding that by launching the unit, Shahid Tondgouyan oil refinery no longer needs to take super gasoline to improve the quality of gasoline being produced by the refinery.
Compared with the Euro 382.46/1,000 litres recorded on April 4, average pre-tax prices of unleaded Euro-super (95 octane rating) in the EU-25 shot up to Euro 399.40/1,000 litres on April 18.
Gasoline with an octane rating of 95 will remain in the range of P48.05 to P58.82 a liter, while kerosene will now be at P46.07 to P56.25 a liter.