The octane rating is a measure of the autoignition resistance of gasoline and other fuels used in spark-ignition internal combustion engines. The autoignition temperature or kindling point of a substance is the lowest temperature at which it will spontaneously ignite in a normal atmosphere without an external A spark plug (also very rarely nowadays in British English: a sparking plug) is an electrical device that fits into the Cylinder The internal combustion engine is an engine in which the Combustion of Fuel and an Oxidizer (typically air occurs in a confined space called a It is a measure of anti-detonation of a gasoline or fuel.
Octane number is the number which gives the percentage, by volume, of iso-octane in a mixture of iso-octane and normal heptane, that would have the same anti-knocking capacity as the fuel which is under consideration. 224-Trimethylpentane, also known as isooctane, is an Octane Isomer which defines the 100 point on the Octane rating scale n -Heptane is the straight-chain Alkane with the Chemical formula H3C(CH25CH3 or C7H16 For example, gasoline with the same knocking characteristics as a mixture of 90% iso-octane and 10% heptane would have an octane rating of 90. Knocking (also called knock, detonation or spark knock, pinking in UK English or pinging in US English in spark-ignition 224-Trimethylpentane, also known as isooctane, is an Octane Isomer which defines the 100 point on the Octane rating scale n -Heptane is the straight-chain Alkane with the Chemical formula H3C(CH25CH3 or C7H16 [1]
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Definition of octane rating
The octane rating of a spark ignition engine fuel is the knock resistance (anti-knock rating) compared to a mixture of iso-octane (2,2,4-trimethylpentane, an isomer of octane) and n-heptane. 224-Trimethylpentane, also known as isooctane, is an Octane Isomer which defines the 100 point on the Octane rating scale This article is about the chemical concept For "isomerism" of atomic nuclei see Nuclear isomer. Octane is a straight-chain Alkane with the Chemical formula CH3(CH26CH3 n -Heptane is the straight-chain Alkane with the Chemical formula H3C(CH25CH3 or C7H16 By definition, iso-octane is assigned an octane rating of 100 and heptane is assigned an octane rating of zero. An 87-octane gasoline, for example, possesses 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 has the same autoignition resistance as the described mixture.
A high tendency to autoignite, or low octane rating, is undesirable in a spark ignition engine but desirable in a diesel engine. The standard for the combustion quality of diesel fuel is the cetane number. Diesel or Diesel fuel (ˈdiːzəl in general is any Fuel used in Diesel engines The most common is a specific fractional distillate of petroleum Cetane number or CN is a measurement of the Combustion quality of Diesel fuel during compression ignition A diesel fuel with a high cetane number has a high tendency to autoignite, as is preferred.
It should be noted that octane rating does not relate to the energy content of the fuel (see heating value), nor the speed at which the flame initiated by the spark plug propagates across the cylinder. The heat of combustion (ΔHc0 is the Energy released as Heat when a compound undergoes complete Combustion with Oxygen It is only a measure of the fuel's resistance to autoignition. It is for this reason that one highly branched form, or isomer, of octane (2,2,4-trimethylpentane) has (by definition) an octane rating of 100, whereas n-octane (see octane), which has a linear arrangement of the 8 carbon atoms, has an octane rating of -10, even though the two fuels have exactly the same chemical formula and virtually identical heating values and flame speeds. This article is about the chemical concept For "isomerism" of atomic nuclei see Nuclear isomer. 224-Trimethylpentane, also known as isooctane, is an Octane Isomer which defines the 100 point on the Octane rating scale Octane is a straight-chain Alkane with the Chemical formula CH3(CH26CH3
Measurement methods
The most common type of octane rating worldwide is the Research Octane Number (RON). RON is determined by running the fuel in a test engine with a variable compression ratio under controlled conditions, and comparing these results with those for mixtures of iso-octane and n-heptane. An engine is a mechanical device that produces some form of output from a given input The compression ratio is a single number that can be used to predict the performance of any engine particularly piston engines (but can be used on essentially any Internal-combustion
There is another type of octane rating, called Motor Octane Number (MON) or the aviation lean octane rating, which is a better measure of how the fuel behaves when under load. MON testing uses a similar test engine to that used in RON testing, but with a preheated fuel mixture, a higher engine speed, and variable ignition timing to further stress the fuel's knock resistance. An ignition system is a system for igniting a fuel-air mixture Depending on the composition of the fuel, the MON of a modern gasoline will be about 8 to 10 points lower than the RON. Normally fuel specifications require both a minimum RON and a minimum MON.
In most countries (including all of Europe and Australia) the "headline" octane that would be shown on the pump is the RON, but in the United States, Canada and some other countries the headline number is the average of the RON and the MON, sometimes called the Anti-Knock Index (AKI), Road Octane Number (RdON), Pump Octane Number (PON), or (R+M)/2. For a topic outline on this subject see List of basic Australia topics. The United States of America —commonly referred to as the Country to "Dominion of Canada" or "Canadian Federation" or anything else please read the Talk Page Because of the 8 to 10 point difference noted above, this means that the octane in the United States will be about 4 to 5 points lower than the same fuel elsewhere: 87 octane fuel, the "regular" gasoline in the US and Canada, would be 91-92 in Europe. The United States of America —commonly referred to as the Country to "Dominion of Canada" or "Canadian Federation" or anything else please read the Talk Page However most European pumps deliver 95 (RON) as "regular", equivalent to 90-91 US (R+M)/2, and even deliver 98 (RON) or 100 (RON).
The octane rating may also be a "trade name", with the actual figure being higher than the nominal rating.
It is possible for a fuel to have a RON greater than 100, because iso-octane is not the most knock-resistant substance available. Racing fuels, straight ethanol, AvGas and liquified petroleum gas (LPG) typically have octane ratings of 110 or significantly higher - ethanol's RON is 129 (MON 102, AKI 116) reference[1]. Avgas is a high-octane Aviation fuel used for Aircraft and Racing cars Avgas is a Portmanteau for aviation gasoline Liquefied petroleum gas (also called LPG, GPL, LP Gas, or Autogas) is a mixture of Hydrocarbon Gases used as a Fuel Typical "octane booster" additives include tetra-ethyl lead, MTBE and toluene. Tetra-ethyl lead, abbreviated TEL, is an organometallic compound with the formula ( CH3CH2)4 Pb. Methyl tert -butyl ether, also known as methyl tertiary butyl ether and MTBE, is a Chemical compound with molecular formula C5H12O Toluene, also known as methylbenzene or phenylmethane, is a clear water -insoluble liquid with the typical smell of Paint thinners redolent of Tetra-ethyl lead is easily decomposed to its component radicals, which react with the radicals from the fuel and oxygen that would start the combustion, thereby delaying ignition. This is why leaded gasoline has a higher octane rating than unleaded.
Examples of octane ratings
The octane ratings of n-heptane and iso-octane are respectively exactly 0 and 100, by definition. n -Heptane is the straight-chain Alkane with the Chemical formula H3C(CH25CH3 or C7H16 For some other hydrocarbons, the following table[2][3] gives the 'AKI' ratings.
| n-octane | -10 |
| n-heptane | 0 |
| 2-methylheptane | 23 |
| n-hexane | 25 |
| 2-methylhexane | 44 |
| Hydrogen* | >50 |
| 1-heptene | 60 |
| n-pentane | 62 |
| 1-pentene | 84 |
| n-butane | 91 |
| cyclohexane | 97 |
| iso-octane | 100 |
| benzene | 101 |
| E85 Ethanol | 105 |
| Methane | 107 |
| Ethane | 108 |
| Methanol | 113 |
| Toluene | 114 |
| Ethanol | 116 |
| Xylene | 117 |
*Hydrogen represents a paradox. Octane is a straight-chain Alkane with the Chemical formula CH3(CH26CH3 n -Heptane is the straight-chain Alkane with the Chemical formula H3C(CH25CH3 or C7H16 Hexane is an Alkane Hydrocarbon with the Chemical formula CH3(CH24CH3 or C6H14 Pentane is any or one of the Organic compounds with the formula C5H12 Cis-2-pentenesvg|thumb|Cis-2-pentene]] Pentene refers to all the Alkenes with Chemical formula 510 containing a single Double bond Butane, also called n -butane, is the unbranched Alkane with four Carbon Atoms CH3CH2CH2CH3 Cyclohexane is a Cycloalkane with the Molecular formula C 6 H 12 224-Trimethylpentane, also known as isooctane, is an Octane Isomer which defines the 100 point on the Octane rating scale Benzene, or benzol, is an organic Chemical compound and a known Carcinogen with the molecular formula C 6 H 6 E85 is an Alcohol fuel mixture that typically contains a mixture of up to 85% denatured fuel ethanol and Gasoline or other hydrocarbon (HC by Methane is a Chemical compound with the molecular formula. It is the simplest Alkane, and the principal component of Natural gas. ETHANE is a mnemonic indicating a protocol used by Emergency services to report situations which they may be faced with especially as it relates to major incidents where Methanol, also known as methyl alcohol, carbinol, wood alcohol, wood naphtha or wood spirits, is a Chemical compound Toluene, also known as methylbenzene or phenylmethane, is a clear water -insoluble liquid with the typical smell of Paint thinners redolent of o-Xylene|m-Xylene|p-XyleneThe term xylene or xylol refers to a mixture of three Benzene derivatives which is used as a Solvent in the Printing As a fuel outright, it has low knock resistance[2][3], due to its low ignition energy (primarily due to its low dissociation energy) and extremely high flame speed. However, as a minor blending component (i. e. , a bi-fuel vehicle), hydrogen raises overall knock resistance. Flame speed is limited by the rest of the component species; hydrogen may reduce knock by contributing its high thermal conductivity. These traits are highly desirable in rocket engines, but undesirable in Otto-cycle engines.
Effects of octane rating
Higher octane ratings correlate to higher activation energies. In Chemistry, activation energy, also called midnight energy, is a term introduced in 1889 by the Swedish scientist Svante Arrhenius, that is defined Activation energy is the amount of energy necessary to start a chemical reaction. Since higher octane fuels have higher activation energies, it is less likely that a given compression will cause knocking. Knocking (also called knock, detonation or spark knock, pinking in UK English or pinging in US English in spark-ignition (Note that it is the absolute pressure (compression) in the combustion chamber which is important — not the compression ratio. The compression ratio only governs the maximum compression that can be achieved).
Octane rating has no direct impact on the deflagration (burn) of the air/fuel mixture in the combustion chamber. Deflagration (Lat de + flagrare, "to burn down" is a technical term describing subsonic Combustion that usually propagates through Thermal conductivity Other properties of gasoline and engine design account for the manner at which deflagration takes place. In other words, the flame speed of a normally ignited mixture is not directly connected to octane rating. Deflagration is the type of combustion that constitutes the normal burn. Detonation is a different type of combustion and this is to be avoided in spark ignited gasoline engines. Detonation is a process of Supersonic Combustion in which a Shock wave is propagated forward due to energy release in a reaction zone behind it Octane rating is a measure of detonation resistance, not deflagration characteristics.
It might seem odd that fuels with higher octane ratings explode less easily and are therefore more powerful. One simple explanation for the effect is that various fuels can provide different heat (therefore energy) at different compression levels. As the compression level increases on many fuels so does the heat (energy) per unit of measure of fuel. Fuels burned in normal sea level pressure produce less energy than ones burned at the point of pre-ignition. The best energy pressure (compression ratio) for a fuel is at the point of where the engine "pings". Each fuel with its own resistance to pre-ignition requires its own ideal compression ratio. This is not always what emission levels require however. A motor must be constructed to work within a fuels compression ratio and emission levels.
Another simple explanation is that carbon-carbon bonds contain more energy than carbon-hydrogen bonds. Hence a fuel with a greater number of carbon bonds will carry more energy regardless of the octane rating. A premium motor fuel will often be formulated to have both higher octane as well as more energy. A counter example to this rule is that ethanol blend fuels have a higher octane rating, but carry a lower energy content by volume (per litre or per gallon). This is because ethanol is a partially oxidized hydrocarbon which can be seen by noting the presence of oxygen in the chemical formula: C2H5OH. Oxygen (from the Greek roots ὀξύς (oxys (acid literally "sharp" from the taste of acids and -γενής (-genēs (producer literally begetteris the Note the substitution of the OH hydroxyl group for a H hydrogen which transforms the gas ethane (C2H6) into ethanol. Hydroxyl in Chemistry stands for a molecule consisting of an Oxygen atom and a Hydrogen atom connected by a Covalent bond. Hydrogen (ˈhaɪdrədʒən is the Chemical element with Atomic number 1 ETHANE is a mnemonic indicating a protocol used by Emergency services to report situations which they may be faced with especially as it relates to major incidents where To a certain extent a fuel with a higher carbon ratio will be more dense than a fuel with a lower carbon ratio. Thus it is possible to formulate high octane fuels that carry less energy per liter than lower octane fuels. This is certainly true of ethanol blend fuels (gasohol), however fuels with no ethanol and indeed no oxygen are also possible. Ethanol (ethyl Alcohol) and Methanol (methyl alcohol are two types of Alcohol fuels.
Alcohol fuels such as methanol and ethanol, are partially oxidized fuels and need to be run at much richer mixtures than gasoline. Methanol, also known as methyl alcohol, carbinol, wood alcohol, wood naphtha or wood spirits, is a Chemical compound As a consequence, the total volume of fuel burned per cycle counterbalances the lower energy per unit volume, and the net energy released per cycle is higher. If gasoline is run at its preferred maximum power air/fuel mixture of 12. 5:1, it will release approximately 20 MJ (about 19,000 BTU) of energy, where ethanol run at its preferred maximum power mixture of 6. 5:1 will liberate approximately 25. 7 MJ (24,400 BTU), and methanol at a 4. 5:1 AFR liberates about 29. 1 MJ (27,650 BTU). To account for these differences, a measure called the fuel's specific energy is sometimes used. It is defined as the energy released per air/fuel ratio. Energy density is the amount of Energy stored in a given system or region of space per unit Volume, or per unit Mass, depending on the context although
Using a fuel with a higher octane lets an engine run at a higher compression ratio without having problems with knock. Actual compression in the combustion chamber is determined by the compression ratio as well as the amount of air restriction in the intake manifold (manifold vacuum) as well as the barometric pressure, which is a function of elevation and weather conditions.
Compression is directly related to power (see engine tuning), so engines that require higher octane usually deliver more power. Engine tuning is the adjustment modification or design of Internal combustion engines to yield optimal performance either in terms of power output or economy Engine power is a function of the fuel as well as the engine design and is related to octane ratings of the fuel. Power is limited by the maximum amount of fuel-air mixture that can be forced into the combustion chamber. A combustion chamber is the part of an Engine in which Fuel is burned At partial load, only a small fraction of the total available power is produced because the manifold is operating at pressures far below atmospheric. In Automotive engineering, an intake manifold or inlet manifold is the part of an Engine that supplies the Fuel / Air mixture to In this case, the octane requirement is far lower than what is available. It is only when the throttle is opened fully and the manifold pressure increases to atmospheric (or higher in the case of supercharged or turbocharged engines) that the full octane requirement is achieved. A throttle is the mechanism by which the flow of a fluid is managed by constriction or obstruction Manifold vacuum, or engine Vacuum in an internal combustion engine is the difference in air pressure between the engine's intake manifold and A supercharger is an air compressor used for Forced induction of an Internal combustion engine. A turbocharger, or turbo, is an air Compressor used for forced-induction of an Internal combustion engine.
Many high-performance engines are designed to operate with a high maximum compression and thus need a high quality (high energy) fuel usually associated with high octane numbers and thus demand high-octane premium gasoline. Ethanol with an octane of 116 could be a high performance fuel if engines were designed with a 14 to 1 compression ratio, possibly improving the mileage to compete with gasoline. The Offenhauser engine had a 15 to 1 ratio and burned methanol. Offenhauser was a racing engine manufacturer that operated from 1933 to 1983 The power output of an engine depends on the energy content of its fuel, and this bears no simple relationship to the octane rating. A common understanding that may apply in only limited circumstances amongst petrol consumers is that adding a higher octane fuel to a vehicle's engine will increase its performance and/or lessen its fuel consumption; this may be false under most conditions — while engines perform best when using fuel with the octane rating for which they were designed and any increase in performance by using a fuel with a different octane rating is minimal or even imaginary, unless there are carbon hotspots, fuel injector clogging or other conditions that may cause a lean situation that can cause knocking that are more common in high mileage vehicles, which would cause modern cars to retard timing thus leading to a loss of both responsiveness and fuel economy. This also does not apply to turbocharged vehicles, which may be allowed to run greater advance in certain circumstances due to external temperatures.
Using high octane fuel for an engine makes a difference when the engine is producing its maximum power or when under a high load such as climbing a large hill or carrying excessive weight. This will occur when the intake manifold has no air restriction and is running at minimum vacuum. Depending on the engine design, this particular circumstance can be anywhere along the RPM range, but is usually easy to pinpoint if you can examine a printout of the power output (torque values) of an engine. On a typical high-revving motorcycle engine, for example, the maximum power occurs at a point where the movements of the intake and exhaust valves are timed in such a way to maximize the compression loading of the cylinder; although the piston is already rising at the time the intake valve closes, the forward speed of the charge coming into the cylinder is high enough to continue to load the air-fuel mixture in.
When this occurs, if a fuel with below recommended octane is used, the engine will knock. Modern engines have anti-knock provisions built into the control systems and this is usually achieved by dynamically de-tuning the engine while under load by increasing the fuel-air mixture and retarding the spark. Here is a link to a white paper that gives an example: [4]. In this example, the engine maximum power is reduced by about 4% with a fuel switch from 93 to 91 octane (11 hp, from 291 to 280 hp). If the engine is being run below maximum load, the difference in octane will have even less effect. The example cited does not indicate at what elevation the test is being conducted or what the barometric pressure is. For each 1000 feet of altitude the atmospheric pressure will drop by a little less than 11 kPa/km (1 inHg). Inches of mercury, inHg or "Hg is a measuring unit for Pressure. An engine that might require 93 octane at sea level may perform at maximum on a fuel rated at 91 octane if the elevation is over, say, 1000 feet. See also the APC article. Automatic Performance Control (APC was the first engine knock and boost control system that was introduced on turbo charged Saab H engines in 1982 and was
The octane rating was developed by chemist Russell Marker at the Ethyl Corporation c1926. Russell Earl Marker ( March 12, 1902 &ndash March 23, 1995) was an eccentric American Chemist who invented the octane Ethyl Corporation is a fuel additive company headquartered in Richmond Virginia. The selection of n-heptane as the zero point of the scale was due to the availability of very high purity n-heptane, not mixed with other isomers of heptane or octane, distilled from the resin of the Jeffrey Pine. n -Heptane is the straight-chain Alkane with the Chemical formula H3C(CH25CH3 or C7H16 This article is about the chemical concept For "isomerism" of atomic nuclei see Nuclear isomer. Octane is a straight-chain Alkane with the Chemical formula CH3(CH26CH3 Resin, not to be confused with Rosin, is a Hydrocarbon Secretion of many Plants particularly coniferous trees. Jeffrey Pine ( Pinus jeffreyi) named in honor of its documenter John Jeffrey, is a North American Pine related to Ponderosa Pine Other sources of heptane produced from crude oil contain a mixture of different isomers with greatly differing ratings, which would not give a precise zero point.
Regional variations
Octane ratings can vary greatly from region to region. For example, the minimum octane rating available in much of the United States is 87 AKI and the highest is 93. However this does not mean that the gas is different.
In the Rocky Mountain (high altitude) states, 85 octane is the minimum octane and 91 is the maximum octane available in fuel. The reason for this is that in higher-altitude areas, a typical combustion engine draws in less air per cycle due to the reduced density of the atmosphere. This directly translates to reduced absolute compression in the cylinder, therefore deterring knock. It is safe to fill up a car with a carburetor that normally takes 87 AKI fuel at sea level with 85 AKI fuel in the mountains, but at sea level the fuel may cause damage to the engine. A disadvantage to this strategy is that most turbocharged vehicles are unable to produce full power, even when using the "premium" 91 AKI fuel. In some east coast states, up to 94 AKI is available [5]. In parts of the Midwest (primarily Minnesota, Iowa, Illinois and Missouri) ethanol based E-85 fuel with 105 AKI is available [6]. E85 is an Alcohol fuel mixture that typically contains a mixture of up to 85% denatured fuel ethanol and Gasoline or other hydrocarbon (HC by
California fuel stations will offer 87, 89, and 91 octane fuels, and at some stations, 100 or higher octane, sold as racing fuel. Until Summer 2001, 92 octane was offered in lieu of 91.
Generally, octane ratings are higher in Europe than they are in North America and most other parts of the world. This is especially true when comparing the lowest available octane level in each country. In many parts of Europe, 95 RON (90-91 AKI) is the minimum available standard, with 97/98 being higher specification (being called Super Unleaded). In Germany, big suppliers like Shell or Aral offer 100 octane gasoline (Shell V-Power, Aral Ultimate) at almost every gas station. Germany, officially the Federal Republic of Germany ( ˈbʊndəsʁepuˌbliːk ˈdɔʏtʃlant is a Country in Central Europe. Royal Dutch Shell plc, commonly known simply as Shell, is a multinational oil company of Dutch and British origins Aral is a brand of automobile fuels and Gas stations, present in Germany and Luxembourg, but formerly In Australia, "regular" unleaded fuel is RON 91, "premium" unleaded with RON 95 is widely available, and RON 98 fuel is also reasonably common. For a topic outline on this subject see List of basic Australia topics. Shell sells RON 100 petrol from a small number of service stations, most of which are located in capital cities. In Malaysia, the "regular" unleaded fuel is RON92 while "premium" fuel is rated at RON97. In other countries "regular" unleaded gasoline, when available, is sometimes as low as 85 RON (still with the more regular fuel - 95 - and premium around 98 available). In Russia and CIS countries 80 RON (76 AKI) is the minimum available and the standard. Russia (Россия Rossiya) or the Russian Federation ( Rossiyskaya Federatsiya) is a transcontinental Country extending
It should be noted that this higher rating seen in Europe is an artifact of a different underlying measuring procedure. In most countries (including all of Europe and Australia) the "headline" octane that would be shown on the pump is the RON, but in the United States, Canada and some other countries the headline number is the average of the RON and the MON, sometimes called the Anti-Knock Index (AKI), Road Octane Number (RdON), Pump Octane Number (PON), or (R+M)/2. Because of the 8 to 10 point difference noted above, this means that the octane in the United States will be about 4 to 5 points lower than the same fuel elsewhere: 87 octane fuel, the "regular" gasoline in the US and Canada, would be 91-92 in Europe. However most European pumps deliver 95 (RON) as "regular", equivalent to 90-91 US (R+M)/2, and deliver 98 (RON), 99 or 100 (RON) labeled as Super Unleaded.
In the United Kingdom, 'regular' petrol has an octane rating of 95 RON, with 97 RON fuel being widely available. The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom, the UK or Britain,is a Sovereign state located Tescos and Shell both offer 99 RON fuel. Tesco plc is a British -based international grocery and general merchandising retail chain Royal Dutch Shell plc, commonly known simply as Shell, is a multinational oil company of Dutch and British origins BP is currently trialling the public selling of the super-high octane petrol BP Ultimate Unleaded 102, which as the name suggests, has an octane rating of RON 102. BP plc, previously known as British Petroleum, is the third largest global Energy company, a multinational oil company (" Oil major Octane is a straight-chain Alkane with the Chemical formula CH3(CH26CH3 Although BP Ultimate Unleaded (with an octane rating of RON 97) and BP Ultimate Diesel are both widely available throughout the UK, BP Ultimate Unleaded 102 is (as of October 2007) only available throughout the UK in 10 filling stations.
References
- ^ Page 992. Brown, Theodore, and LeMay, Eugene, et al. Chemistry: The Central Science. Ninth edition. Pearson Education Inc. Upper Saddle River, NJ. 2003. ISBN 0-13-066997-0.
- ^ Petroleum and Coal
- ^ http://www.iupac.org/publications/pac/1983/pdf/5502x0199.pdf
See also
External links
Octane ratings of some hydrocarbons
Information in general
- 116 Octane With Water Injection Alcoholinjectionsystems. Avgas is a high-octane Aviation fuel used for Aircraft and Racing cars Avgas is a Portmanteau for aviation gasoline com
- Reduce Detonation With Water Injection Alcoholinjecionsystems. com
Khoo, Kenny K. Understanding Octane and its Related Components. Yellowknife: Smithsonian Press, 2006.
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