Gasoline //, known as
petrol // outside of
North America, is a transparent,
petroleum-derived liquid that is used primarily as a fuel in
internal combustion engines. It consists mostly of
organic compounds obtained by the
fractional distillation of petroleum, enhanced with a variety of additives; a 42-gallon barrel of crude oil yields about 19 gallons of gasoline, when processed in an
oil refinery.
The characteristic of a particular gasoline blend to resist igniting too early (which causes knocking and reduces efficiency in reciprocating engines) is measured by its
octane rating. Gasoline is produced in several grades of octane rating.
Tetraethyllead and other lead compounds are no longer used in most areas to regulate and increase octane-rating, but many other additives are put into gasoline to improve its chemical stability, control corrosiveness and provide fuel system 'cleaning,' and determine performance characteristics under intended use. Sometimes, gasoline also contains
ethanol as an
alternative fuel, for economic or environmental reasons.
Gasoline, as used worldwide in the vast number of internal combustion engines used in transport and industry, has a significant impact on the environment, both in local effects (e.g., smog) and in global effects (e.g.,
effect on the climate). Gasoline may also enter the environment uncombusted, as liquid and as vapors, from leakage and handling during production, transport and delivery, from storage tanks, from spills, etc. As an example of efforts to control such leakage, many (underground) storage tanks are required to have extensive measures in place to detect and prevent such leaks. The
material safety data sheet for unleaded gasoline shows at least 15 hazardous chemicals occurring in various amounts. Benzene and many anti-knocking additives are
carcinogenic.
Inhaled (huffed) gasoline vapor is a common intoxicant that has become epidemic in some poorer communities and indigenous groups in Australia, Canada, New Zealand, and some Pacific Islands.
[1] In response,
Opal fuel has been developed by the
BP Kwinana Refinery in Australia, and contains only 5%
aromatics (unlike the usual 25%), which weakens the effects of inhalation.
[2]
Octane rating
Spark ignition engines are designed to burn gasoline in a controlled process called
deflagration. In some cases, however, the unburned mixture can autoignite by detonating from pressure and heat alone, rather than ignite from the spark plug at exactly the right time, which causes rapid pressure rise which can damage the engine. This phenomenon is often referred to as
engine knocking or end-gas knock. One way to reduce knock in spark ignition engines is to increase the gasoline's resistance to
autoignition, which is expressed by its octane rating.
Octane rating 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 is the standard for regular unleaded gasoline and 98 RON is also available as a more expensive option. In the UK, ordinary regular unleaded gasoline is 95 RON (commonly available), premium unleaded gasoline is always 97 RON, and super unleaded is usually 97-98 RON.
[citation needed] However, both Shell and BP produce fuel at 102 RON for cars with high-performance engines, and the supermarket chain
Tesco began in 2006 to sell super unleaded gasoline rated at 99 RON. In the US, octane ratings in unleaded fuels can vary between 85
[3] and 87 AKI (91-92 RON) for regular, through 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).
South Africa's largest city,
Johannesburg, is located on the
Highveld at 1,753 metres (5,751 ft) above sea level. So the
South African AA recommends 95 octane petrol (gasoline) as low altitude and 93 octane for use in Johannesburg because "The higher the altitude the lower the air pressure, and the lower the need for a high octane fuel as there is no real performance gain".
[4]
The octane rating became important as the military sought higher output for
aircraft engines in the late 1930s 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 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 1320 horsepower (984 kW) using 100 RON fuel from a modest 27 liter displacement. Towards the end of the
second world war, experiments were conducted using 150 RON fuel (100/150
[clarification needed] avgas), obtained by adding 2.5% aniline to 100 octane avgas.
[5]
Stability
Quality gasoline should be stable for six months if stored properly but gasoline will break down slowly over time due to the separation of the components. Gasoline stored for a year will most likely be able to be burned in an internal combustion engine without too much trouble but 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 the older gasoline may be used up. If left undiluted, improper operation will occur and this may include engine damage from misfiring and/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). Storage should be in an airtight container (to prevent oxidation or water vapors mixing in with 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 be created, which can corrode system components and accumulate on wetted surfaces, resulting in 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, 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, the buildup may or may not 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. Some typical fuel stabilizers are proprietary mixtures containing
mineral spirits,
isopropyl alcohol, 1,2,4-trimethylbenzene,or other additives. Fuel stabilizer is commonly used for small engines, such as lawnmower and tractor engines, especially when their use is seasonal (low 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.
[6]
Energy content
Energy is obtained from the combustion of gasoline by the conversion of a hydrocarbon to
carbon dioxide and
water. The combustion of octane follows this reaction:
- 2 C8H18 + 25 O2 → 16 CO2 + 18 H2O
Gasoline contains about 42.4
MJ/kg (120 MJ/US gal, 33.3 kWh/US gal) quoting the lower heating value
[citation needed]. Gasoline blends differ, and therefore actual energy content varies according to the season and producer by up to 4% more or less than the average, according to the US EPA. On average, about 74 L of gasoline (19.5 US gal, 16.3 imp gal) are available from a barrel of crude oil (about 46% by volume), varying due to quality of crude and grade of gasoline. The remainder are products ranging from tar to naphtha.
[7]
A high-octane-rated fuel, such as
liquefied petroleum gas (LPG) has an overall lower power output at the typical 10:1
compression ratio of a gasoline engine. However, with an engine
tuned to the
use of LPG (i.e. via higher compression ratios, such as 12:1 instead of 10:1), the power output can be improved. 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 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 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 air flow.
The lower energy content (per liter) of LPG in comparison to gasoline is due mainly to its lower
density. Energy content per kilogram is higher than for gasoline (higher
hydrogen to
carbon ratio, for an example see
Standard enthalpy of formation).
Molecular weights of the above reagents are C
8H
18 114, O
2 32, CO
2 44, H
2O 18; therefore 1 kg of fuel reacts with 3.51 kg of oxygen to produce 3.09 kg of carbon dioxide and 1.42 kg of water.
Density
The density of gasoline ranges from 0.71–0.77 kg/L (
719.7 kg/m3 ; 0.026
lb/
in3; 6.073 lb/
US gal; 7.29 lb/
imp gal), higher densities having a greater volume of aromatics.
[8] Since gasoline floats on water, water cannot generally be used to extinguish a gasoline fire unless used in a fine mist. Finished marketable gasoline is traded with a standard reference of 0.755 kg/L, and its price is escalated/de-escalated according to its actual density.
Chemical analysis and production
Gasoline is produced in
oil refineries. Roughly 19 gallons of gasoline is derived from a 42 gallon 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.
Some of the main components of gasoline:
isooctane,
butane, 3-ethyltoluene, and the octane enhancer
MTBE.
The bulk of a typical gasoline consists of
hydrocarbons with between 4 and 12
carbon atoms per
molecule (commonly referred to as C4-C12).
[6] It is a mixture of paraffins (
alkanes),
cycloalkanes (naphthenes), and olefins (
alkenes), where the usage of the terms paraffin and olefin is particular to the oil industry. The actual ratio depends on:
- the oil refinery that makes the gasoline, as not all refineries have the same set of processing units;
- the crude oil feed used by the refinery;
- the grade of gasoline, in particular, the octane rating.
The various
refinery streams blended to make gasoline have different characteristics. Some important streams are:
- straight-run gasoline, usually also called naphtha is distilled directly from crude oil. Once the leading source of fuel, its low octane rating required lead additives. It is low in aromatics (depending on the grade of crude oil), containing some cycloalkanes (naphthenes) and no olefins (alkenes). Between 0 and 20% of this stream is pooled into the finished gasoline, because the supply of this fraction is insufficient[clarification needed] and its RON is too low.[citation needed]. The chemical properties (namely octane and RVP) of the straight-run gasoline can be improved through reforming and isomerisation. However, before feeding those units, the naphtha needs to be split in light and heavy naphtha. Straight-run gasoline can be also used as a feedstock into steam-crackers to produce olefins.
- reformate, produced in a catalytic reformer has a high octane rating with high aromatic content, and relatively low olefins (alkenes). Most of the benzene, toluene, and xylene (the so-called BTX) are more valuable as chemical feedstocks and are thus removed to some extent.
- catalytic cracked gasoline or catalytic cracked naphtha, produced from a catalytic cracker, with a moderate octane rating, high olefins (alkene) content, and moderate aromatics level.
- hydrocrackate (heavy, mid, and light) produced from a hydrocracker, with medium to low octane rating and moderate aromatic levels.
- alkylate is produced in an alkylation unit, using as feedstocks isobutane and alkenes. Alkylate contains no aromatics and alkenes and has high MON[clarification needed].
- isomerate is obtained by isomerizing low octane straight run gasoline to iso-paraffins (non-chain alkanes, like isooctane). Isomerate has medium RON and MON, but nil aromatics and olefins.
The terms above are the
jargon used in the oil industry and terminology varies.
Currently, many countries set limits on gasoline
aromatics in general,
benzene in particular, and olefin (alkene) content. Such regulations led to increasing preference for high octane pure paraffin (alkane) components, such as alkylate, and is forcing refineries to add processing units to reduce benzene content. In the EU the benzene limit is set at 1% volume for all grade of automotive gasoline.
Gasoline can also contain other
organic compounds, such as
organic ethers (deliberately added), plus small levels of contaminants, in particular
organosulfur compounds, but these are usually removed at the refinery.
Additives
Antiknock additives
A plastic container for storing gasoline used in Germany
Almost all countries in the world have phased out automotive leaded fuel. In 2011 six countries
[9] in the world were still using leaded gasoline:
Afghanistan,
Myanmar,
North Korea,
Algeria,
Iraq and
Yemen. It was expected that by the end of 2013 those countries would ban leaded petrol,
[10] but actually it will take longer. Algeria will replace leaded with unleaded automotive fuel only in 2015. Different additives have replaced the lead compounds. The most popular additives include
aromatic hydrocarbons,
ethers and
alcohol (usually
ethanol or
methanol). For technical reasons the use of leaded additives is still permitted world-wide for the formulation of some grades of
aviation gasoline such as
100LL, because the required octane rating would be technically infeasible to reach without the use of leaded additives.
Tetraethyllead
Gasoline, when used in high-
compression internal combustion engines, tends to autoignite (
detonate) causing damaging "
engine knocking" (also called "pinging" or "pinking") noise. To address this problem,
tetraethyllead (TEL) was widely adopted as an additive for gasoline in the 1920s. With the discovery of the extent of environmental and health damage caused by the lead, however, and the incompatibility of lead with
catalytic converters, leaded gasoline was phased out beginning in 1973.
By 1995, leaded fuel accounted for only 0.6% of total gasoline sales and less than 2000
short tons (1814 t) of lead per year in the USA. From 1 January 1996, the
U.S. Clean Air Act banned the sale of leaded fuel for use in on-road vehicles in the USA. The use of TEL also necessitated other additives, such as dibromoethane. First European countries started replacing lead by the end of the 1980s and by the end of the 1990s leaded petrol was banned within the entire European Union.
MMT
Methylcyclopentadienyl manganese tricarbonyl (MMT) is used in Canada and in Australia to boost octane. It also helps old cars designed for leaded fuel run on unleaded fuel without need for additives to prevent valve problems. Its use in the US has been restricted by regulations.
Fuel stabilizers (antioxidants and metal deactivators)
Substituted
phenols and derivatives of
phenylenediamine are common antioxidants used to inhibit gum formation in gasoline (gasoline).
Gummy, sticky resin deposits result from
oxidative degradation of gasoline upon long term storage. These harmful deposits arise from 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 are most susceptible to oxidation. The formation of these gums is accelerated by copper salts, which can be neutralized by additives called
metal deactivators.
This degradation can be prevented through the addition of 5–100 ppm of
antioxidants, such as
phenylenediamines and other
amines.
[6] 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 the gasoline.
[11]
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.
Detergents
Gasoline, as delivered at the pump, also contains additives to reduce internal engine carbon buildups, improve
combustion, and to 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 was developed by four automakers: GM, Honda, Toyota and BMW. According to the bulletin, the minimal EPA requirement is not sufficient to keep engines clean.
[12] Typical detergents include alkylamines and alkyl phosphates at the level of 50-100 ppm.
[6]
Ethanol
European Union
In the EU, 5% ethanol can be added within the common gasoline spec (EN 228). Discussions are ongoing to allow 10% blending of ethanol (available in Finnish, French and German gas stations). In Finland most gasoline stations sell 95E10, which is 10% of ethanol; and 98E5, which is 5% ethanol. Most gasoline sold in Sweden has 5-15% ethanol added.
Brazil
In Brazil, the
Brazilian National Agency of Petroleum, Natural Gas and Biofuels (ANP) requires gasoline for automobile use, to have from 18 to 25% of ethanol added to its composition.
[13]
Australia
Legislation requires retailers to label fuels containing ethanol on the dispenser, and limits ethanol use to 10% of petrol in Australia. Such petrol is commonly called
E10 by major brands, and it is cheaper than regular unleaded petrol.
United States of America
The federal
Renewable Fuel Standard (RFS) effectively requires refiners and blenders to blend renewable biofuels (mostly ethanol) with gasoline, sufficient to meet 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 has caused the typical ethanol content in gasoline to approach 10%. Most fuel pumps display a sticker that states that the fuel may contain up to 10% ethanol, an intentional disparity that reflects the varying actual percentage. Until late 2010, fuels retailers were only authorized to sell fuel containing up to 10 percent ethanol (E10), and most vehicle warranties (except for flexible fuel vehicles) authorize fuels that contain no more than 10 percent ethanol.
[14] In parts of the United States,
ethanol is sometimes added to gasoline without an indication that it is a component.
India
The
Government of India in October 2007 decided to make 5% ethanol blending (with gasoline) mandatory. Currently, 10% Ethanol blended product (E10) is being sold in various parts of the country.
[15][16]
Dye
In Australia, the lowest grade of petrol (RON 91) is dyed a light shade of red/orange and the medium grade (RON 95) is dyed yellow.
[17]
In the United States, aviation gasoline (
avgas) is dyed to identify its octane rating and to distinguish it from kerosene-based jet fuel, which is clear.
[18]
In Canada the gasoline for marine and farm use is dyed red and is not subject to road tax
[citation needed].
Oxygenate blending
Oxygenate blending adds
oxygen-bearing compounds such as
MTBE,
ETBE and
ethanol. The presence of these oxygenates reduces the amount of
carbon monoxide and unburned fuel in the exhaust gas. In many areas throughout the US, oxygenate blending is mandated by EPA regulations to reduce smog and other airborne pollutants. For example, in Southern California, fuel must contain 2% oxygen by weight, resulting in a mixture of 5.6% 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. The federal requirement that RFG contain oxygen was dropped on 6 May 2006 because the industry had developed
VOC-controlled RFG that did not need additional oxygen.
[19]
MTBE use is being phased out in some states due to issues with contamination of ground water. In some places, such as California, it is already banned. Ethanol and, to a lesser extent, the ethanol-derived ETBE are common replacements. A common ethanol-gasoline mix of 10% ethanol mixed with gasoline is called
gasohol or E10, and an ethanol-gasoline mix of 85% ethanol mixed with gasoline is called
E85. The most extensive use of ethanol takes place in
Brazil, where the ethanol is derived from
sugarcane. In 2004, over 3.4 billion US gallons (2.8 billion imp gal/13 million m³) of ethanol was produced in the United States for fuel use, mostly from
corn, and E85 is slowly becoming available in much of the United States, though many of the relatively few stations vending E85 are not open to the general public.
[20] The use of
bioethanol, either directly or indirectly by conversion of such ethanol to bio-ETBE, is encouraged by the European Union
Directive on the Promotion of the use of biofuels and other renewable fuels for transport. Since producing bioethanol from fermented sugars and starches involves
distillation, though, ordinary people in much of Europe cannot legally ferment and distill their own bioethanol at present (unlike in the US, where getting a
BATF distillation permit has been easy since the 1973 oil crisis).
Safety
Environmental considerations
Combustion of 1 US gallon (3.8 L) of gasoline produces 8,788 grams (19.374 lb) of carbon dioxide (2.3 kg/l), a
greenhouse gas.
[21]
The main concern with gasoline on the environment, aside from the complications of its extraction and refining, is the potential
effect on the climate. Unburnt gasoline and
evaporation from the tank, when in the
atmosphere, react in
sunlight to produce
photochemical smog. Vapor pressure initially rises with some addition of ethanol to gasoline, but the increase is greatest at 10% by volume. At higher concentrations of ethanol above 10%, the vapor pressure of the blend starts to decrease. At a 10% ethanol by volume, the rise in vapor pressure may potentially increase the problem of photochemical smog. This rise in vapor pressure could be mitigated by increasing the percentage of ethanol in the gasoline mixture.
The chief risks of such leaks come not from vehicles, but from gasoline delivery truck accidents and leaks from storage tanks. Because of this risk, most (underground) storage tanks now have extensive measures in place to detect and prevent any such leaks, such as monitoring systems (Veeder-Root, Franklin Fueling).
Toxicity
The
material safety data sheet for unleaded gasoline shows at least 15 hazardous chemicals occurring in various amounts, including
benzene (up to 5% by volume),
toluene (up to 35% by volume),
naphthalene (up to 1% by volume),
trimethylbenzene (up to 7% by volume),
methyl tert-butyl ether (MTBE) (up to 18% by volume, in some states) and about ten others.
[22] Hydrocarbons in gasoline generally exhibit low acute toxicities, with
LD50 of 700 – 2700 mg/kg for simple aromatic compounds.
[23] Benzene and many antiknocking additives are
carcinogenic.
Inhalation
Huffed gasoline is a common intoxicant that has become epidemic in some poorer communities and indigenous groups in Australia, New Zealand, and some Pacific Islands.
[1] In response,
Opal fuel has been developed by the
BP Kwinana Refinery in Australia, and contains only 5%
aromatics (unlike the usual 25%), which weakens the effects of inhalation.
[2]
Flammability
Like other hydrocarbons, gasoline burns in a limited range of its vapor phase and, coupled with its volatility, this makes leaks highly dangerous when sources of ignition are present. Gasoline has a lower explosion limit of 1.4% by volume and an upper explosion limit of 7.6%. If the concentration is below 1.4%, the air-gasoline mixture is too lean and does not ignite. If the concentration is above 7.6%, the mixture is too rich and also does not ignite. However, gasoline vapor rapidly mixes and spreads with air, making unconstrained gasoline quickly flammable.
Use and pricing
The United States accounts for about 44% of the world’s gasoline consumption.
[24] In 2003 The US consumed 476
gigaliters (126
billion U.S. gallons; 105 billion
imperial gallons),
[25] which equates to 1.3 gigaliters (340 million U.S. gallons; 290 million imperial gallons) of gasoline each day. The US used about 510 gigaliters (130 billion U.S. gallons; 110 billion imperial gallons) of gasoline in 2006, of which 5.6% was mid-grade and 9.5% was premium grade.
[26]
Europe
Unlike the US, countries in Europe impose substantial
taxes on fuels such as gasoline. The price of gasoline in Europe is typically more than twice that in the US. In Italy, due to the amendments imposed by
Monti's Government in December 2011, the price of gasoline has passed, in the period of two weeks, from 1.50 €/l (7.48 US$/gal) to 1.75 €/l (8.72 US$/gal); on March 17, a gasoline station located near
Ancona has reached the psychological threshold of 2 €/l: the price was €2.001/l (9.97 US$/gal). This chart must be compared to the USA national average price of gasoline of 0.71 €/l.
Pump price (in Euro/liter) 2004 to 2012 lead-free 95 Octane gasoline in selected European countries.
To convert prices for Euro/liter to US$/gal, multiply by 4.84 (16 Oct 2014 US$1.28 = 1.00 Euro).
| Germany |
1.19 |
1.18 |
1.37 |
1.43 |
1.09 |
1.35 |
1.50 |
| France |
1.05 |
1.15 |
1.31 |
1.38 |
1.07 |
1.35 |
1.53 |
| Italy |
1.10 |
1.23 |
1.35 |
1.39 |
1.10 |
1.34 |
1.46 |
1.75 |
1.78 |
1.88 |
1.82 |
| Netherlands |
1.26 |
1.33 |
1.51 |
1.56 |
1.25 |
1.54 |
1.66 |
1.72 |
| Poland |
0.80 |
0.92 |
1.15 |
1.23 |
0.82 |
1.12 |
1.26 |
| Switzerland |
0.92 |
0.98 |
1.06 |
1.14 |
0.88 |
1.12 |
1.29 |
1.40 |
1.47 |
| Hungary |
1.00 |
1.01 |
1.13 |
1.13 |
0.86 |
1.22 |
1.32 |
1.38 |
1.44 |
1.47 |
1.55 |
United States
From 1998 to 2004, the price of gasoline fluctuated between $1 and $2
USD per
U.S. gallon.
[27]
After 2004, the price increased until the average gas price reached a high of $4.11 per U.S. gallon in mid-2008, but receded to approximately $2.60 per U.S. gallon by September 2009.
[27] More recently, the U.S. experienced an upswing in gas prices through 2011,
[28] and by 1 March 2012, the national average was $3.74 per gallon.
In the United States, most consumer goods bear pre-tax prices, but gasoline prices are posted with taxes included. Taxes are added by federal, state, and local governments. As of 2009, the federal tax is 18.4¢ per gallon for gasoline and 24.4¢ per gallon for diesel (excluding
red diesel).
[29] Among states, the highest gasoline tax rates, including the federal taxes as of 2005, are New York (62.9¢/gal), Hawaii (60.1¢/gal), and California (60¢/gal).
[28] However, many states' taxes are a percentage and thus vary in amount depending on the cost of the gasoline.
About 9% of all gasoline sold in the US in May 2009 was premium grade, according to the Energy Information Administration.
Consumer Reports magazine says, “If [your owner’s manual] says to use regular fuel, do so—there’s no advantage to a higher grade.”
[30] The Associated Press said premium gas—which is a higher octane and costs more per gallon than regular unleaded—should be used only if the manufacturer says it is “required”.
[31] Cars with turbocharged engines and high compression ratios often specify premium gas because higher octane fuels reduce the incidence of "knock", or fuel pre-detonation.
[32] If regular fuel is used, the engine computer usually switches to a less aggressive fuel map to protect the engine, and performance is decreased.
Mid grade unleaded gasoline was introduced in the 1970s when leaded gas was phased out. The reason is that unleaded fuel builds up carbon deposits on the piston whereas leaded fuel causes the carbon deposits to flake off. At around 15000 miles every car using regular grade needs to change to mid grade to avoid pinging from hot spot predetonation. While modern cars use knock sensors to retard timing to avoid pinging, to maintain original engine performance mid grade should be used. Mid grade is also used by some manufacturers to increase engine power, and if so, then they would need to start using premium grade at around 15000 miles to maintain their original performance.
History
The first automotive combustion engines, so-called
Otto engines, were developed in the last quarter of the 19th century in Germany. The fuel was a relatively volatile hydrocarbon obtained from
coal gas. With a boiling point near 85 °C (octanes boil about 40 °C higher), it 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 knocking (premature explosion of fuel). In the 1920s, antiknock compounds were introduced by Migley and Boyd, specifically
tetraethyllead (TEL). This innovation started a cycle of improvements in fuel efficiency that coincided with the large-scale development of oil refining to provide more products in the boiling range of gasolines. In the 1950s oil refineries started to focus on high octane fuels, and then detergents were added to gasoline to clean the jets and carburetors. The 1970s witnessed greater attention to the environmental consequences of burning gasoline. These considerations led to the phasing out of TEL and its replacement by other antiknock compounds. Subsequently, low-sulfur gasoline was introduced, in part to preserve the catalysts in modern exhaust systems.
[6]
Etymology and terminology
"Gasoline" is cited (under the spelling "gasolene") from 1863 in the
Oxford English Dictionary. It was never a trademark, although it may have been derived from older trademarks such as "Cazeline" and "Gazeline".
[33]
Variant spellings of "gasoline" have been used to refer to raw
petroleum since the 16th century.
[33] "Petrol" was first used as the name of a refined petroleum product around 1870 by British wholesaler
Carless, Capel & Leonard, who marketed it as a solvent.
[34] When the product later found a new use as a motor fuel,
Frederick Simms, an associate of
Gottlieb Daimler, suggested to Carless that they register the trade mark "petrol",
[35] but by this time the word was already in general use, possibly inspired by the French
pétrole,
[33] and the registration was not allowed. Carless registered a number of alternative names for the product, while their competitors used the term "motor spirit" until the 1930s.
[36][37]
In many countries, gasoline has a colloquial name derived from that of the chemical
benzene (
e.g., German
Benzin, Dutch
benzine, Italian
benzina, Polish
benzyna, Chilean Spanish
bencina, Thai เบนซิน
bayn sin , Greek βενζίνη
venzini, Romanian
benzină, Swedish
bensin, Arabic بنزين
binzīn). Argentina, Uruguay and Paraguay use the colloquial name
nafta derived from that of the chemical
naphtha.
[38]
The terms "mogas", short for motor gasoline, or "autogas", short for automobile gasoline, are used to distinguish
automobile fuel from aviation fuel, or "
avgas".
[39][40][41]
Comparison with other fuels
Volumetric and mass
energy density of some fuels compared with gasoline (in the rows with
gross and
net, they are from
[42]):
| Conventional gasoline |
34.8 |
44.4[43] |
150,100 |
125,000 |
115,400 |
91-92 |
| Autogas (LPG) (Consisting mostly of C2 to C4 range hydrocarbons)[citation needed] |
26.8 |
46 |
5,587 |
6,710 |
|
108 |
| Ethanol |
21.2[43] |
26.8[43] |
101,600 |
84,600 |
75,700 |
108.7[44] |
| Methanol |
17.9 |
19.9[43] |
77,600 |
64,600 |
56,600 |
123 |
| Butanol[4] |
29.2 |
36.6 |
6,087 |
7,311 |
|
91-99[clarification needed] |
| Gasohol |
31.2 |
|
145,200 |
120,900 |
112,400 |
93/94[clarification needed] |
| Diesel(*) |
38.6 |
45.4 |
166,600 |
138,700 |
128,700 |
25 |
| Biodiesel |
33.3-35.7[45][clarification needed] |
|
|
126,200 |
117,100 |
|
| Avgas (high octane gasoline) |
33.5 |
46.8 |
144,400 |
120,200 |
112,000 |
|
| Jet fuel (kerosene based) |
35.1 |
43.8 |
151,242 |
125,935 |
|
|
| Jet fuel (naphtha) |
|
|
|
127,500 |
118,700 |
|
| Liquefied natural gas |
25.3 |
~55 |
109,000 |
90,800 |
|
|
| Liquefied petroleum gas |
|
46.1 |
|
91,300 |
83,500 |
|
| Hydrogen |
10.1 (at 20 kelvin) |
142 |
|
|
130[46] |
(*) Diesel fuel is not used in a gasoline engine, so its low octane rating is not an issue; the relevant metric for diesel engines is the cetane number
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