Misplaced Pages

#220779

98-640: Octane is a component of gasoline and petroleum. Under standard temperature and pressure , octane is an odorless, colorless liquid. Like other short-chained alkanes with a low molecular weight, it is volatile , flammable, and toxic. Octane is 1.2 to 2 times more toxic than heptane . N-octane has 23 constitutional isomers . 8 of these isomers have one stereocenter ; 3 of them have two stereocenters. Achiral Isomers: Chiral Isomers: In petrochemistry, octanes are not typically differentiated or purified as specific compounds. Octanes are components of particular boiling fractions. A common route to such fractions

196-415: A knock sensor that monitors if knock is being produced by the fuel being used. In modern computer-controlled engines, the ignition timing will be automatically altered by the engine management system to reduce the knock to an acceptable level. Octanes are a family of hydrocarbons that are typical components of gasoline. They are colorless liquids that boil around 125 °C (260 °F). One member of

294-456: A condition called "stale fuel". Gasoline containing ethanol is especially subject to absorbing atmospheric moisture, then forming gums, solids, or two phases (a hydrocarbon phase floating on top of a water-alcohol phase). The presence of these degradation products in the fuel tank or fuel lines plus a carburetor or fuel injection components makes it harder to start the engine or causes reduced engine performance On resumption of regular engine use,

392-449: A controlled process called deflagration . However, the unburned mixture may autoignite by pressure and heat alone, rather than igniting from the spark plug at exactly the right time, causing a rapid pressure rise that can damage the engine. This is often referred to as engine knocking or end-gas knock. Knocking can be reduced by increasing the gasoline's resistance to autoignition , which is expressed by its octane rating. Octane rating

490-443: A fine mist. Quality gasoline should be stable for six months if stored properly, but can degrade over time. Gasoline stored for a year will most likely be able to be burned in an internal combustion engine without too much trouble. However, the effects of long-term storage will become more noticeable with each passing month until a time comes when the gasoline should be diluted with ever-increasing amounts of freshly made fuel so that

588-413: A flame wave initiate at the spark plug and then "travel in a fairly uniform manner across the combustion chamber" with the expanding gas mix pushing the piston throughout the entirety of the power stroke. A stable gasoline and air mix will combust when the flame wave reaches the molecules, adding heat at the interface. Knock occurs when a secondary flame wave forms from instability and then travels against

686-400: A fuel for engines , gasoline is chemically composed of organic compounds derived from the fractional distillation of petroleum and later chemically enhanced with gasoline additives . It is a high-volume profitable product produced in crude oil refineries. The fuel-characteristics of a particular gasoline-blend, which will resist igniting too early are measured as the octane rating of

784-470: A greater volume fraction of aromatics. Finished marketable gasoline is traded (in Europe) with a standard reference of 0.755 kilograms per liter (6.30 lb/U.S. gal), (7,5668 lb/ imp gal) its price is escalated or de-escalated according to its actual density. Because of its low density, gasoline floats on water, and therefore water cannot generally be used to extinguish a gasoline fire unless applied in

882-412: A growing annual target of total gallons blended. Although the mandate does not require a specific percentage of ethanol, annual increases in the target combined with declining gasoline consumption have caused the typical ethanol content in gasoline to approach 10 percent. Most fuel pumps display a sticker that states that the fuel may contain up to 10 percent ethanol, an intentional disparity that reflects

980-574: A high compression ratio. A high expansion ratio is also one of the two key reasons for the efficiency of diesel engines , along with the elimination of pumping losses due to throttling of the intake airflow. The lower energy content of LPG by liquid volume in comparison to gasoline is due mainly to its lower density. This lower density is a property of the lower molecular weight of propane (LPG's chief component) compared to gasoline's blend of various hydrocarbon compounds with heavier molecular weights than propane. Conversely, LPG's energy content by weight

1078-401: A higher compression ratio through the concomitant higher expansion ratio on the power stroke, which is by far the greater effect. The higher expansion ratio extracts more work from the high-pressure gas created by the combustion process. An Atkinson cycle engine uses the timing of the valve events to produce the benefits of a high expansion ratio without the disadvantages, chiefly detonation, of

SECTION 10

#1732780619221

1176-440: A lighter fuel that's less prone to autoignition is a wise "insurance policy". For the same reasons, those lighter fuels which are better solvents are much less likely to cause any "varnish" or other fouling on the "backup" spark plugs. In almost all general aviation piston engines, the fuel mixture is directly controlled by the pilot, via a knob and cable or lever similar to (and next to) the throttle control. Leaning — reducing

1274-643: A nation with a good supply of high-octane gasoline would have the advantage in air power. In 1943, the Rolls-Royce Merlin aero engine produced 980 kilowatts (1,320 hp) using 100 RON fuel from a modest 27 liters (1,600 cu in) displacement. By the time of Operation Overlord , both the RAF and USAAF were conducting some operations in Europe using 150 RON fuel (100/150 avgas ), obtained by adding 2.5 percent aniline to 100-octane avgas. By this time,

1372-486: A relatively low octane rating; the isomer iso-octane causes less knocking because it is more branched and combusts more smoothly. In general, branched compounds with a higher intermolecular force (e.g., London dispersion force for iso-octane) will have a higher octane rating, because they are harder to ignite. Octane isomers such as n-octane and 2,3,3-trimethylpentane have an octane rating of -20 and 106.1, respectively ( RON measurement). The large differences between

1470-417: A representative species, performs the chemical reaction: By weight, combustion of gasoline releases about 46.7 megajoules per kilogram (13.0  kWh /kg; 21.2 MJ/ lb ) or by volume 33.6 megajoules per liter (9.3 kWh/L; 127 MJ/U.S. gal; 121,000 BTU/U.S. gal), quoting the lower heating value . Gasoline blends differ, and therefore actual energy content varies according to

1568-595: A similar test engine to that used in RON testing, but with a preheated fuel mixture, higher engine speed, and variable ignition timing to further stress the fuel's knock resistance. Depending on the composition of the fuel, the MON of a modern pump gasoline will be about 8 to 12 lower than the RON, but there is no direct link between RON and MON. See the table below. In most countries in Europe, and in Australia and New Zealand,

1666-739: Is 10 percent ethanol, and 98E5, which is 5 percent ethanol. Most gasoline sold in Sweden has 5–15 percent ethanol added. Three different ethanol blends are sold in the Netherlands—E5, E10 and hE15. The last of these differs from standard ethanol–gasoline blends in that it consists of 15 percent hydrous ethanol (i.e., the ethanol–water azeotrope ) instead of the anhydrous ethanol traditionally used for blending with gasoline. The Brazilian National Agency of Petroleum, Natural Gas and Biofuels (ANP) requires gasoline for automobile use to have 27.5 percent of ethanol added to its composition. Pure hydrated ethanol

1764-480: Is a measured and/or calculated rating of the fuel's ability to resist autoignition, the higher the octane of the fuel, the harder that fuel is to ignite and the more heat is required to ignite it. The result is that a hotter ignition spark is required for ignition. Creating a hotter spark requires more energy from the ignition system, which in turn increases the parasitic electrical load on the engine. The spark also must begin earlier in order to generate sufficient heat at

1862-493: Is a mixture of many hydrocarbons and often other additives). Octane ratings are not indicators of the energy content of fuels. (See Effects below and Heat of combustion ). They are only a measure of the fuel's tendency to burn in a controlled manner, rather than exploding in an uncontrolled manner. Where the octane number is raised by blending in ethanol, energy content per volume is reduced. Ethanol energy density can be compared with gasoline in heat-of-combustion tables. It

1960-426: Is a mixture of paraffins ( alkanes ), olefins ( alkenes ), napthenes ( cycloalkanes ), and aromatics . The use of the term paraffin in place of the standard chemical nomenclature alkane is particular to the oil industry (which relies extensively on jargon). The composition of a gasoline depends upon: The various refinery streams blended to make gasoline have different characteristics. Some important streams include

2058-457: Is a naturally colorless liquid, many gasolines are dyed in various colors to indicate their composition and acceptable uses. In Australia, the lowest grade of gasoline (RON 91) was dyed a light shade of red/orange, but is now the same color as the medium grade (RON 95) and high octane (RON 98), which are dyed yellow. In the U.S., aviation gasoline ( avgas ) is dyed to identify its octane rating and to distinguish it from kerosene-based jet fuel, which

SECTION 20

#1732780619221

2156-452: Is also available as a fuel. Legislation requires retailers to label fuels containing ethanol on the dispenser, and limits ethanol use to 10 percent of gasoline in Australia. Such gasoline is commonly called E10 by major brands, and it is cheaper than regular unleaded gasoline. The federal Renewable Fuel Standard (RFS) effectively requires refiners and blenders to blend renewable biofuels (mostly ethanol) with gasoline, sufficient to meet

2254-460: Is called E85 . The most extensive use of ethanol takes place in Brazil , where the ethanol is derived from sugarcane . In 2004, over 13 billion liters (3.4 × 10 ^  U.S. gal) of ethanol was produced in the U.S. for fuel use, mostly from corn and sold as E10. E85 is slowly becoming available in much of the U.S., though many of the relatively few stations vending E85 are not open to

2352-478: Is derived from a 160-liter (42 U.S. gal) barrel of crude oil . Material separated from crude oil via distillation , called virgin or straight-run gasoline, does not meet specifications for modern engines (particularly the octane rating ; see below), but can be pooled to the gasoline blend. The bulk of a typical gasoline consists of a homogeneous mixture of hydrocarbons with between 4 and 12 carbon atoms per molecule (commonly referred to as C4–C12). It

2450-425: Is derived from testing the gasoline in ordinary multi-cylinder engines (rather than in a purpose-built test engine), normally at wide open throttle. This type of test was developed in the 1920s and is still reliable today. The original RdON tests were done in cars on the road, but as technology developed the testing was moved to chassis dynamometers with environmental controls to improve consistency. The evaluation of

2548-490: Is higher than gasoline's due to a higher hydrogen -to- carbon ratio. Molecular weights of the species in the representative octane combustion are 114, 32, 44, and 18 for C 8 H 18 , O 2 , CO 2 , and H 2 O, respectively; therefore one kilogram (2.2 lb) of fuel reacts with 3.51 kilograms (7.7 lb) of oxygen to produce 3.09 kilograms (6.8 lb) of carbon dioxide and 1.42 kilograms (3.1 lb) of water. Spark-ignition engines are designed to burn gasoline in

2646-427: Is ignited only near the end of the compression stroke by electric spark plugs . Therefore, being able to compress the air/fuel mixture without causing detonation is important mainly for gasoline engines. Using gasoline with lower octane than an engine is built for may cause engine knocking and/or pre-ignition . The octane rating of aviation gasoline was extremely important in determining aero engine performance in

2744-422: Is left colorless. In Canada, the gasoline for marine and farm use is dyed red and is not subject to fuel excise tax in most provinces. Oxygenate blending adds oxygen -bearing compounds such as MTBE , ETBE , TAME , TAEE , ethanol , and biobutanol . The presence of these oxygenates reduces the amount of carbon monoxide and unburned fuel in the exhaust. In many areas throughout the U.S., oxygenate blending

2842-501: Is mandated by EPA regulations to reduce smog and other airborne pollutants. For example, in Southern California fuel must contain two percent oxygen by weight, resulting in a mixture of 5.6 percent ethanol in gasoline. The resulting fuel is often known as reformulated gasoline (RFG) or oxygenated gasoline, or, in the case of California, California reformulated gasoline (CARBOB). The federal requirement that RFG contain oxygen

2940-448: Is measured relative to a mixture of 2,2,4-trimethylpentane (an isomer of octane ) and n- heptane . There are different conventions for expressing octane ratings, so the same physical fuel may have several different octane ratings based on the measure used. One of the best known is the research octane number (RON). The octane rating of typical commercially available gasoline varies by country. In Finland , Sweden , and Norway , 95 RON

3038-411: Is possible for a fuel to have a Research Octane Number (RON) more than 100, because iso-octane is not the most knock-resistant substance available today. Racing fuels, avgas , LPG and alcohol fuels such as methanol may have octane ratings of 110 or significantly higher. Typical "octane booster" gasoline additives include MTBE , ETBE , iso-octane and toluene . Lead in the form of tetraethyllead

Octane - Misplaced Pages Continue

3136-458: Is sporadic or seasonal (little to no use for one or more seasons of the year). Users have been advised to keep gasoline containers more than half full and properly capped to reduce air exposure, to avoid storage at high temperatures, to run an engine for ten minutes to circulate the stabilizer through all components prior to storage, and to run the engine at intervals to purge stale fuel from the carburetor. Gasoline stability requirements are set by

3234-437: Is the alkylation reaction between iso-butane and 1-butene, which forms iso-octane. Octane is commonly used as a solvent in paints and adhesives. Gasoline Gasoline ( North American English ) or petrol ( Commonwealth English ) is a petrochemical product characterized as a transparent, yellowish, and flammable liquid normally used as a fuel for spark-ignited internal combustion engines . When formulated as

3332-435: Is the octane number of the fuel. 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. A rating of 90 does not mean that the gasoline contains just iso-octane and heptane in these proportions, but that it has the same detonation resistance properties (generally, gasoline sold for common use never consists solely of iso-octane and heptane; it

3430-493: Is the standard for regular unleaded gasoline and 98 RON is also available as a more expensive option. In the United Kingdom, over 95 percent of gasoline sold has 95 RON and is marketed as Unleaded or Premium Unleaded. Super Unleaded, with 97/98 RON and branded high-performance fuels (e.g., Shell V-Power, BP Ultimate) with 99 RON make up the balance. Gasoline with 102 RON may rarely be available for racing purposes. In

3528-763: Is used in Canada and the U.S. to boost octane rating. Its use in the U.S. has been restricted by regulations, although it is currently allowed. Its use in the European Union is restricted by Article 8a of the Fuel Quality Directive following its testing under the Protocol for the evaluation of effects of metallic fuel-additives on the emissions performance of vehicles. Gummy, sticky resin deposits result from oxidative degradation of gasoline during long-term storage. These harmful deposits arise from

3626-449: The U.S. Clean Air Act banned the sale of leaded fuel for use in on-road vehicles in the U.S. The use of TEL also necessitated other additives, such as dibromoethane . European countries began replacing lead-containing additives by the end of the 1980s, and by the end of the 1990s, leaded gasoline was banned within the entire European Union with an exception for Avgas 100LL for general aviation . The UAE started to switch to unleaded in

3724-557: The four-stroke cycle . In a simple explanation, the forward moving wave of combustion that burns the hydrocarbon + oxygen mixture inside the cylinder like a wave that a surfer would wish to surf upon is violently disrupted by a secondary wave that has started elsewhere. The shock wave of these two separate waves creates the characteristic metallic "pinging" sound, and cylinder pressure increases dramatically. Effects of engine knocking range from inconsequential (incremental heating plus power loss) to completely destructive (detonation while one of

3822-423: The ideal gas law . Higher compression ratios necessarily add parasitic load to the engine, and are only necessary if the engine is being specifically designed to run on high-octane fuel. Aircraft engines run at relatively low speeds and are " undersquare ". They run best on lower-octane, slower-burning fuels that require less heat and a lower compression ratio for optimum vaporization and uniform fuel-air mixing, with

3920-543: The "headline" octane rating prominently displayed on the pump is the RON, but in Canada, the United States, and Mexico, the headline number is the simple mean or average of the RON and the MON, called the Anti-Knock Index ( AKI ), and often written on pumps as (R+M)/2 . AKI is also sometimes called PON (Pump Octane Number). Because of the 8 to 12 octane number difference between RON and MON noted above,

4018-551: The AKI shown in Canada and the United States is 4 to 6 octane numbers lower than elsewhere in the world for the same fuel. This difference between RON and MON is known as the fuel's sensitivity, and is not typically published for those countries that use the Anti-Knock Index labelling system. See the table in the following section for a comparison. Another type of octane rating, called Observed Road Octane Number ( RdON ),

Octane - Misplaced Pages Continue

4116-477: The Rolls-Royce Merlin 66 was developing 1,500 kilowatts (2,000 hp) using this fuel. Gasoline, when used in high- compression internal combustion engines, tends to auto-ignite or "detonate" causing damaging engine knocking (also called "pinging" or "pinking"). To address this problem, tetraethyl lead (TEL) was widely adopted as an additive for gasoline in the 1920s. With a growing awareness of

4214-692: The U.S., octane ratings in unleaded fuels vary between 85 and 87 AKI (91–92 RON) for regular, 89–90 AKI (94–95 RON) for mid-grade (equivalent to European regular), up to 90–94 AKI (95–99 RON) for premium (European premium). As South Africa's largest city, Johannesburg , is located on the Highveld at 1,753 meters (5,751 ft) above sea level, the Automobile Association of South Africa recommends 95-octane gasoline at low altitude and 93-octane for use in Johannesburg because "The higher

4312-410: The addition of 5–100 ppm of antioxidants , such as phenylenediamines and other amines . Hydrocarbons with a bromine number of 10 or above can be protected with the combination of unhindered or partially hindered phenols and oil-soluble strong amine bases, such as hindered phenols. "Stale" gasoline can be detected by a colorimetric enzymatic test for organic peroxides produced by oxidation of

4410-404: The aircraft of World War II . The octane rating affected not only the performance of the gasoline, but also its versatility; the higher octane fuel allowed a wider range of lean to rich operating conditions. In spark ignition internal combustion engines , knocking (also knock , detonation , spark knock , pinging , or pinking ) occurs when combustion of some of the air/fuel mixture in

4508-457: The altitude the lower the air pressure, and the lower the need for a high octane fuel as there is no real performance gain". Octane rating became important as the military sought higher output for aircraft engines in the late 1920s and the 1940s. A higher octane rating allows a higher compression ratio or supercharger boost, and thus higher temperatures and pressures, which translate to higher power output. Some scientists even predicted that

4606-588: The announcement "the end of one toxic era". However, leaded gasoline continues to be used in aeronautic, auto racing, and off-road applications. The use of leaded additives is still permitted worldwide for the formulation of some grades of aviation gasoline such as 100LL , because the required octane rating is difficult to reach without the use of leaded additives. Different additives have replaced lead compounds. The most popular additives include aromatic hydrocarbons , ethers ( MTBE and ETBE ), and alcohols , most commonly ethanol . Lead replacement petrol (LRP)

4704-403: The available air) or "lean of peak" (less fuel, leaving some oxygen in the exhaust) as either will keep the fuel-air mixture from detonating prematurely. Because of the high cost of unleaded, high-octane avgas , and possible increased range before refueling, some general aviation pilots attempt to save money by tuning their fuel-air mixtures and ignition timing to run "lean of peak". Additionally,

4802-521: The benzene limit is set at one percent by volume for all grades of automotive gasoline. This is usually achieved by avoiding feeding C6, in particular cyclohexane , to the reformer unit, where it would be converted to benzene. Therefore, only (desulfurized) heavy virgin naphtha (HVN) is fed to the reformer unit Gasoline can also contain other organic compounds , such as organic ethers (deliberately added), plus small levels of contaminants, in particular organosulfur compounds (which are usually removed at

4900-612: The buildup may or may not be eventually cleaned out by the flow of fresh gasoline. The addition of a fuel stabilizer to gasoline can extend the life of fuel that is not or cannot be stored properly, though removal of all fuel from a fuel system is the only real solution to the problem of long-term storage of an engine or a machine or vehicle. Typical fuel stabilizers are proprietary mixtures containing mineral spirits , isopropyl alcohol , 1,2,4-trimethylbenzene or other additives . Fuel stabilizers are commonly used for small engines, such as lawnmower and tractor engines, especially when their use

4998-413: The cylinder does not result from propagation of the flame front ignited by the spark plug , but when one or more pockets of air/fuel mixture explode outside the envelope of the normal combustion front. The fuel-air charge is meant to be ignited by the spark plug only, and at a precise point in the piston's stroke. Knock occurs when the peak of the combustion process no longer occurs at the optimum moment for

SECTION 50

#1732780619221

5096-421: The decreased air density at higher altitudes (such as Colorado) and temperatures (as in summer) requires leaning (reduction in amount of fuel per volume or mass of air) for the peak EGT and power (crucial for takeoff). The selection of octane ratings available at filling stations can vary greatly between countries. Due to its name, the chemical "octane" is often misunderstood as the only substance that determines

5194-482: The definition of octane rating. The following table lists octane ratings for various other fuels. Higher octane ratings correlate to higher activation energies : the amount of applied energy required to initiate combustion. Since higher octane fuels have higher activation energy requirements, it is less likely that a given compression will cause uncontrolled ignition, otherwise known as autoignition, self-ignition, pre-ignition, detonation, or knocking. Because octane

5292-597: The direct measurements required for research or motor octane numbers. An octane index can be of great service in the blending of gasoline. Motor gasoline, as marketed, is usually a blend of several types of refinery grades that are derived from different processes such as straight-run gasoline, reformate, cracked gasoline etc. These different grades are blended in amounts that will meet final product specifications. Most refiners produce and market more than one grade of motor gasoline, differing principally in their anti-knock quality. Being able to make sufficiently accurate estimates of

5390-519: The early 2000s. Reduction in the average lead content of human blood may be a major cause for falling violent crime rates around the world including South Africa. A study found a correlation between leaded gasoline usage and violent crime (see Lead–crime hypothesis ). Other studies found no correlation. In August 2021, the UN Environment Programme announced that leaded petrol had been eradicated worldwide, with Algeria being

5488-418: The end of production for cars using leaded gasoline in member states. At this stage, a large percentage of cars from the 1980s and early 1990s which ran on leaded gasoline were still in use, along with cars that could run on unleaded fuel. However, the declining number of such cars on British roads saw many gasoline stations withdrawing LRP from sale by 2003. Methylcyclopentadienyl manganese tricarbonyl (MMT)

5586-507: The engine. Lighter and "thinner" fuel also has a lower specific heat , so the practice of running an engine "rich" to use excess fuel to aid in cooling requires richer and richer mixtures as octane increases. Higher-octane, lower-energy-dense "thinner" fuels often contain alcohol compounds incompatible with the stock fuel system components, which also makes them hygroscopic . They also evaporate away much more easily than heavier, lower-octane fuel which leads to more accumulated contaminants in

5684-401: The evaluation of the anti-knock quality of gasoline. Such substitute methods include FTIR, near infrared on-line analyzers, and others. Deriving an equation that can be used to calculate ratings accurately enough would also serve the same purpose, with added advantages. The term Octane Index is often used to refer to the use of an equation to determine a theoretical rating, in contradistinction to

5782-405: The following: The terms above are the jargon used in the oil industry, and the terminology varies. Currently, many countries set limits on gasoline aromatics in general, benzene in particular, and olefin (alkene) content. Such regulations have led to an increasing preference for alkane isomers, such as isomerate or alkylate, as their octane rating is higher than n-alkanes. In the European Union,

5880-510: The fuel blend. Gasoline blends with stable octane ratings are produced in several fuel-grades for various types of motors. A low octane rated fuel may cause engine knocking and reduced efficiency in reciprocating engines . Tetraethyl lead was once widely used to increase the octane rating but are not used in modern automotive gasoline due to the health hazard . Aviation, off-road motor vehicles, and racing car motors still use leaded gasolines. Interest in gasoline-like fuels started with

5978-424: The fuel per unit mass or volume, but simply indicates the resistance to detonating under pressure without a spark. Whether or not a higher octane fuel improves or impairs an engine's performance depends on the design of the engine. In broad terms, fuels with a higher octane rating are used in higher-compression gasoline engines , which may yield higher power for these engines. The added power in such cases comes from

SECTION 60

#1732780619221

6076-406: The fuel system. It is typically the hydrochloric acids that form due to that water and the compounds in the fuel that have the most detrimental effects on the engine fuel system components, as such acids corrode many metals used in gasoline fuel systems. During the compression stroke of an internal combustion engine, the temperature of the air-fuel mix rises as it is compressed, in accordance with

6174-419: The gas) that can withstand the vapor pressure of the gasoline without venting (to prevent the loss of the more volatile fractions) at a stable cool temperature (to reduce the excess pressure from liquid expansion and to reduce the rate of any decomposition reactions). When gasoline is not stored correctly, gums and solids may result, which can corrode system components and accumulate on wet surfaces, resulting in

6272-653: The gasoline. Gasolines are also treated with metal deactivators , which are compounds that sequester (deactivate) metal salts that otherwise accelerate the formation of gummy residues. The metal impurities might arise from the engine itself or as contaminants in the fuel. Gasoline, as delivered at the pump, also contains additives to reduce internal engine carbon buildups, improve combustion and allow easier starting in cold climates. High levels of detergent can be found in Top Tier Detergent Gasolines . The specification for Top Tier Detergent Gasolines

6370-403: The general public. Octane rating An octane rating , or octane number , is a standard measure of a fuel 's ability to withstand compression in an internal combustion engine without causing engine knocking . The higher the octane number, the more compression the fuel can withstand before detonating. Octane rating does not relate directly to the power output or the energy content of

6468-449: The ignition spark coming as late as possible in order to extend the production of cylinder pressure and torque as far down the power stroke as possible. The main reason for using high-octane fuel in air-cooled engines is that it is more easily vaporized in a cold carburetor and engine and absorbs less intake air heat which greatly reduces the tendency for carburetor icing to occur. With their reduced densities and weight per volume of fuel,

6566-461: The invention of internal combustion engines suitable for use in transportation applications. The so-called Otto engines were developed in Germany during the last quarter of the 19th century. The fuel for these early engines was a relatively volatile hydrocarbon obtained from coal gas . With a boiling point near 85 °C (185 °F) ( n -octane boils at 125.62 °C (258.12 °F) ), it

6664-400: The last country to deplete its reserves. UN Secretary-General António Guterres called the eradication of leaded petrol an "international success story". He also added: "Ending the use of leaded petrol will prevent more than one million premature deaths each year from heart disease, strokes and cancer, and it will protect children whose IQs are damaged by exposure to lead". Greenpeace called

6762-446: The lifespan of engines. In 1927, Graham Edgar devised the method of using iso-octane and n-heptane as reference chemicals, in order to rate the knock resistance of a fuel with respect to this isomer of octane, thus the name "octane rating". By definition, the isomers iso-octane and n-heptane have an octane rating of 100 and 0, respectively. Because of its more volatile nature, n-heptane ignites and knocks readily, which gives it

6860-657: The lower of the two. One is referred to as the "aviation lean" rating, which for ratings up to 100 is the same as the MON of the fuel. The second is the "aviation rich" rating and corresponds to the octane rating of a test engine under forced induction operation common in high-performance and military piston aircraft. This utilizes a supercharger , and uses a significantly richer fuel/air ratio for improved detonation resistance. The most common currently used fuel, 100LL , has an aviation lean rating of 100 octane, and an aviation rich rating of 130. The RON/MON values of n- heptane and iso-octane are exactly 0 and 100, respectively, by

6958-445: The mixture from its maximum amount — must be done with knowledge, as some combinations of fuel mixture and throttle position (that produce the highest ) can cause detonation and/or pre-ignition , in the worst case destroying the engine within seconds. Pilots are taught in primary training to avoid settings that produce the highest exhaust gas temperatures, and run the engine either "rich of peak EGT " (more fuel than can be burned with

7056-479: The octane family, 2,2,4-Trimethylpentane (iso-octane), is used as a reference standard to benchmark the tendency of gasoline or LPG fuels to resist self-ignition. The octane rating of gasoline is measured in a test engine and is defined by comparison with the mixture of 2,2,4-trimethylpentane (iso-octane) and normal heptane that would have the same anti-knocking capability as the fuel under test. The percentage, by volume, of 2,2,4-trimethylpentane in that mixture

7154-401: The octane number by either of the two laboratory methods requires a special engine built to match the tests' rigid standards, and the procedure can be both expensive and time-consuming. The standard engine required for the test may not always be available, especially in out-of-the-way places or in small or mobile laboratories. These and other considerations led to the search for a rapid method for

7252-493: The octane rating (or octane number) of a fuel. This is an inaccurate description. In reality, the octane rating is defined as a number describing the stability and ability of a fuel to prevent an engine from unwanted combustions that occur spontaneously in the other regions within a cylinder (i.e., delocalized explosions from the spark plug). This phenomenon of combustion is more commonly known as engine knocking or self-ignition, which causes damage to pistons over time and reduces

7350-470: The octane rating of gasoline is not directly related to the power output of an engine. Using gasoline of a higher octane than an engine is designed for cannot increase its power output. Octane became well known in American popular culture in the 1960s, when gasoline companies boasted of "high octane" levels in their gasoline advertisements. The compound adjective "high-octane", meaning powerful or dynamic,

7448-404: The octane rating that will result from blending different refinery products is essential, something for which the calculated octane index is specially suited. Aviation gasolines used in piston aircraft engines common in general aviation have a slightly different method of measuring the octane of the fuel. Similar to an AKI, it has two different ratings, although it is usually referred to only by

7546-418: The octane ratings for the isomers show that the compound octane itself is clearly not the only factor that determines octane ratings, especially for commercial fuels consist of a wide variety of compounds. "Octane" is colloquially used in the expression "high-octane". The term is used to describe a powerful action because of the association with the concept of "octane rating". This is a misleading term, because

7644-406: The older gasoline may be used up. If left undiluted, improper operation will occur and this may include engine damage from misfiring or the lack of proper action of the fuel within a fuel injection system and from an onboard computer attempting to compensate (if applicable to the vehicle). Gasoline should ideally be stored in an airtight container (to prevent oxidation or water vapor mixing in with

7742-544: The other obvious benefit is that an aircraft with any given volume of fuel in the tanks is automatically lighter. And since many airplanes are flown only occasionally and may sit unused for weeks or months, the lighter fuels tend to evaporate away and leave behind fewer deposits such as "varnish" (gasoline components, particularly alkenes and oxygenates slowly polymerize into solids). Aircraft also typically have dual "redundant" ignition systems which are nearly impossible to tune and time to produce identical ignition timing, so using

7840-455: The oxidation of alkenes and other minor components in gasoline (see drying oils ). Improvements in refinery techniques have generally reduced the susceptibility of gasolines to these problems. Previously, catalytically or thermally cracked gasolines were most susceptible to oxidation. The formation of gums is accelerated by copper salts, which can be neutralized by additives called metal deactivators . This degradation can be prevented through

7938-453: The path of the primary flame wave, thus depriving the power stroke of its uniformity and causing issues including power loss and heat buildup. The other rarely-discussed reality with high-octane fuels associated with "high performance" is that as octane increases, the specific gravity and energy content of the fuel per unit of weight are reduced. The net result is that to make a given amount of power , more high-octane fuel must be burned in

8036-414: The percentage of lighter products compared to simple distillation. Commercial gasoline as well as other liquid transportation fuels are complex mixtures of hydrocarbons. The performance specification also varies with season, requiring less volatile blends during summer, in order to minimize evaporative losses. Gasoline is produced in oil refineries . Roughly 72 liters (19 U.S. gal) of gasoline

8134-454: The phaseout of leaded motor fuels in the United Kingdom, Australia , South Africa , and some other countries. Consumer confusion led to a widespread mistaken preference for LRP rather than unleaded, and LRP was phased out 8 to 10 years after the introduction of unleaded. Leaded gasoline was withdrawn from sale in Britain after 31 December 1999, seven years after EEC regulations signaled

8232-415: The proper time for precise ignition. As octane, ignition spark energy, and the need for precise timing increase, the engine becomes more difficult to "tune" and keep "in tune". The resulting sub-optimal spark energy and timing can cause major engine problems, from a simple "miss" to uncontrolled detonation and catastrophic engine failure. Mechanically within the cylinder, stability can be visualized as having

8330-427: The refinery). On average, U.S. petroleum refineries produce about 19 to 20 gallons of gasoline, 11 to 13 gallons of distillate fuel diesel fuel and 3 to 4 gallons of jet fuel from each 42 gallon (152 liters) barrel of crude oil. The product ratio depends upon the processing in an oil refinery and the crude oil assay . The specific gravity of gasoline ranges from 0.71 to 0.77, with higher densities having

8428-399: The results with those for mixtures of iso-octane and n-heptane. The compression ratio is varied during the test to challenge the fuel's antiknocking tendency, as an increase in the compression ratio will increase the chances of knocking. Another type of octane rating, called Motor Octane Number ( MON ), is determined at 900 rpm engine speed instead of the 600 rpm for RON. MON testing uses

8526-445: The season and producer by up to 1.75 percent more or less than the average. On average, about 74 liters (20 U.S. gal) of gasoline are available from a barrel of crude oil (about 46 percent by volume), varying with the quality of the crude and the grade of the gasoline. The remainder is products ranging from tar to naphtha . A high-octane-rated fuel, such as liquefied petroleum gas (LPG), has an overall lower power output at

8624-701: The seriousness of the extent of environmental and health damage caused by lead compounds, however, and the incompatibility of lead with catalytic converters , governments began to mandate reductions in gasoline lead. In the U.S., the Environmental Protection Agency issued regulations to reduce the lead content of leaded gasoline over a series of annual phases, scheduled to begin in 1973 but delayed by court appeals until 1976. By 1995, leaded fuel accounted for only 0.6 percent of total gasoline sales and under 1,800 metric tons (2,000 short tons; 1,800 long tons) of lead per year. From 1 January 1996,

8722-455: The standard ASTM D4814. This standard describes the various characteristics and requirements of automotive fuels for use over a wide range of operating conditions in ground vehicles equipped with spark-ignition engines. A gasoline-fueled internal combustion engine obtains energy from the combustion of gasoline's various hydrocarbons with oxygen from the ambient air, yielding carbon dioxide and water as exhaust. The combustion of octane ,

8820-408: The typical 10:1 compression ratio of an engine design optimized for gasoline fuel. An engine tuned for LPG fuel via higher compression ratios (typically 12:1) improves the power output. This is because higher-octane fuels allow for a higher compression ratio without knocking, resulting in a higher cylinder temperature, which improves efficiency . Also, increased mechanical efficiency is created by

8918-459: The valves is still open). Knocking should not be confused with pre-ignition —they are two separate events with pre-ignition occurring before the combustion event. However, pre-ignition is highly correlated with knock because knock will cause rapid heat increase within the cylinder eventually leading to destructive pre-detonation. Most engine management systems commonly found in automobiles today, typically electronic fuel injection (EFI), have

9016-510: The varying actual percentage. In parts of the U.S., ethanol is sometimes added to gasoline without an indication that it is a component. In October 2007, the Government of India decided to make five percent ethanol blending (with gasoline) mandatory. Currently, 10 percent ethanol blended product (E10) is being sold in various parts of the country. Ethanol has been found in at least one study to damage catalytic converters. Though gasoline

9114-481: The way the engine is designed to compress the air/fuel mixture, and not directly from the rating of the gasoline. In contrast, fuels with lower octane (but higher cetane numbers ) are ideal for diesel engines because diesel engines (also called compression-ignition engines) do not compress the fuel, but rather compress only air, and then inject fuel into the air that was heated by compression. Gasoline engines rely on ignition of compressed air and fuel mixture, which

9212-633: Was developed by four automakers: GM , Honda , Toyota , and BMW . According to the bulletin, the minimal U.S. EPA requirement is not sufficient to keep engines clean. Typical detergents include alkylamines and alkyl phosphates at a level of 50–100 ppm. In the EU, 5 percent ethanol can be added within the common gasoline spec (EN 228). Discussions are ongoing to allow 10 percent blending of ethanol (available in Finnish, French and German gasoline stations). In Finland, most gasoline stations sell 95E10, which

9310-402: Was developed for vehicles designed to run on leaded fuels and incompatible with unleaded fuels. Rather than tetraethyllead, it contains other metals such as potassium compounds or methylcyclopentadienyl manganese tricarbonyl (MMT); these are purported to buffer soft exhaust valves and seats so that they do not suffer recession due to the use of unleaded fuel. LRP was marketed during and after

9408-478: Was dropped on 6 May 2006 because the industry had developed VOC -controlled RFG that did not need additional oxygen. MTBE was phased out in the U.S. due to groundwater contamination and the resulting regulations and lawsuits. Ethanol and, to a lesser extent, ethanol-derived ETBE are common substitutes. A common ethanol-gasoline mix of 10 percent ethanol mixed with gasoline is called gasohol or E10, and an ethanol-gasoline mix of 85 percent ethanol mixed with gasoline

9506-486: Was once a common additive, but concerns about its toxicity have led to its use for fuels for road vehicles being progressively phased out worldwide beginning in the 1970s. 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 at 600 rpm with a variable compression ratio under controlled conditions, and comparing

9604-516: Was well-suited for early carburetors (evaporators). The development of a "spray nozzle" carburetor enabled the use of less volatile fuels. Further improvements in engine efficiency were attempted at higher compression ratios , but early attempts were blocked by the premature explosion of fuel, known as knocking . In 1891, the Shukhov cracking process became the world's first commercial method to break down heavier hydrocarbons in crude oil to increase

#220779